NUTRITION, METABOLISM, AND

BODY TEMPERATURE REGULATION

NUTRITION

• A nutrient is a substance in food that is used by the body to promote normal growth, maintenance, and repair– Some nutrients are used to build cell structures, replace worn-

out parts, and synthesize functional molecules– Most nutrients are used as metabolic fuel

• They are oxidized and transformed to ATP, the chemical energy form used by cells

• The energy value of foods is measures in kilocalories (kcal) (large calories) ( C )– One kilocalorie is the amount of heat energy needed to raise

the temperature of 1 kilogram of water 1o C (1.8o F) and is then unit conscientiously counted by dieters

NUTRITION

• There are six categories of nutrients: carbohydrates, lipids, proteins, vitamins, minerals, and water

• Essential nutrients are those that cannot be made by the body and must be obtained in the diet

Food Groups

• A diet consisting of foods from each of the five food groups: normally guarantees adequate amounts of all the needed nutrients– Grains– Fruits– Vegetables– Meats– Fish– Milk products

FOOD PYRAMID

New/Old Food Pyramid

New Food Pyramid• The Food Guide Pyramid is one way for people to understand how to

eat healthy. A rainbow of colored, vertical stripes represents the five food groups plus fats and oils. Here's what the colors stand for:

• orange - grains • green - vegetables • red - fruits • yellow - fats and oils • blue - milk and dairy products • purple - meat, beans, fish, and nuts • The U.S. Department of Agriculture (USDA) changed the pyramid in spring

2005 because they wanted to do a better job of telling Americans how to be healthy. The agency later released a special version for kids. Notice the girl climbing the staircase up the side of the pyramid? That's a way of showing kids how important it is to exercise and be active every day. In other words, play a lot! The steps are also a way of saying that you can make changes little by little to be healthier. One step at a time, get it?

Orange/Grains

OrangeGrains (Whole/Refined)

• What foods are in the grain group?Any food made from wheat, rice, oats, cornmeal, barley or another cereal grain is a grain product. Bread, pasta, oatmeal, breakfast cereals, tortillas, and grits are examples of grain products.

Grains are divided into 2 subgroups, whole grains and refined grains.

Whole grains contain the entire grain kernel -- the bran, germ, and endosperm.

• Examples include: – whole-wheat flour – bulgur (cracked wheat) – oatmeal – whole cornmeal – brown rice

OrangeGrains (Whole/Refined)

• Refined grains have been milled, a process that removes the bran and germ. This is done to give grains a finer texture and improve their shelf life, but it also removes dietary fiber, iron, and many B vitamins.

• Some examples of refined grain products are: – white flour – degermed cornmeal – white bread – white rice

• Most refined grains are enriched. This means certain B vitamins (thiamin, riboflavin, niacin, folic acid) and iron are added back after processing. Fiber is not added back to enriched grains. Check the ingredient list on refined grain products to make sure that the word “enriched” is included in the grain name.

• Some food products are made from mixtures of whole grains and refined grains.

Green/Vegetables

Green ColumnVegetable

• What foods are in the vegetable group?Any vegetable or 100% vegetable juice counts as a member of the vegetable group. Vegetables may be raw or cooked; fresh, frozen, canned, or dried/dehydrated; and may be whole, cut-up, or mashed.

Vegetables are organized into 5 subgroups, based on their nutrient content. Some commonly eaten vegetables in each subgroup are:

• Dark green vegetables:• bok choy

broccoli collard greensdark green leafy lettucekalemesclunmustard greensromaine lettucespinachturnip greenswatercress

Green ColumnVegetable

• Dry beans and peas

• black beansblack-eyed peasgarbanzo beans (chickpeas)kidney beanslentilslima beans (mature)navy beanspinto beanssoy beanssplit peastofu (bean curd made from soybeans)white beans

Green ColumnVegetable

• Orange vegetables

• acorn squashbutternut squashcarrotshubbard squashpumpkinsweetpotatoes

Green ColumnVegetable

• Starchy vegetables

• corngreen peaslima beans (green)potatoes

Green ColumnVegetable

• Other vegetables

• artichokesasparagusbean sproutsbeetsBrussels sproutscabbagecauliflowercelerycucumberseggplantgreen beansgreen or red peppersiceberg (head) lettucemushroomsokraonionsparsnipstomatoestomato juicevegetable juiceturnipswax beanszucchini

Red/Fruit

Red/Fruit• What foods are in the fruit group?

Any fruit or 100% fruit juice counts as part of the fruit group. Fruits may be fresh, canned, frozen, or dried, and may be whole, cut-up, or pureed. Some commonly eaten fruits are:

• ApplesApricotsAvocadoBananas

Berries:

• strawberriesblueberriesraspberriescherries

Red/Fruit• Grapefruit

GrapesKiwi fruitLemonsLimesMangoes

Melons:

• cantaloupehoneydewwatermelon

• Mixed fruits:

• fruit cocktail

Red/Fruit• Nectarines

OrangesPeachesPearsPapayaPineapplePlumsPrunesRaisinsTangerines

100% Fruit juice:

• orangeapplegrapegrapefruit

Yellow/Oil

Yellow/Oil• Oils are fats that are liquid at room temperature, like the vegetable oils

used in cooking. Oils come from many different plants and from fish. Some common oils are:

• canola oil • corn oil • cottonseed oil • olive oil • safflower oil • soybean oil • sunflower oil • Some oils are used mainly as flavorings, such as walnut oil and sesame oil.

A number of foods are naturally high in oils, like: • nuts • olives • some fish • avocados

Yellow/Oil• Foods that are mainly oil include mayonnaise, certain salad dressings, and soft (tub or squeeze)

margarine with no trans fats. Check the Nutrition Facts label to find margarines with 0 grams of trans fat. Amounts of trans fat will be required on labels as of 2006. Many products already provide this information.

Most oils are high in monounsaturated or polyunsaturated fats, and low in saturated fats. Oils from plant sources (vegetable and nut oils) do not contain any cholesterol. In fact, no foods from plants sources contain cholesterol.

A few plant oils, however, including coconut oil and palm kernel oil, are high in saturated fats and for nutritional purposes should be considered to be solid fats.

Solid fats are fats that are solid at room temperature, like butter and shortening. Solid fats come from many animal foods and can be made from vegetable oils through a process called hydrogenation. Some common solid fats are:

• butter • beef fat (tallow, suet) • chicken fat • pork fat (lard) • stick margarine • shortening

Light Blue/Milk

Light Blue/Milk• What foods are included in the milk, yogurt, and cheese (milk) group?

• All fluid milk products and many foods made from milk are considered part of this food group. Foods made from milk that retain their calcium content are part of the group, while foods made from milk that have little to no calcium, such as cream cheese, cream, and butter, are not. Most milk group choices should be fat-free or low-fat.

Some commonly eaten choices in the milk, yogurt, and cheese group are:

• Milk*

All fluid milk:

• fat-free (skim)low fat (1%)reduced fat (2%)whole milk

Light Blue/Milk• flavored milks:

• chocolatestrawberry

lactose reduced milkslactose free milks

Milk-based desserts*Puddings made with milkice milkfrozen yogurtice cream

• Cheese*Hard natural cheeses:

• cheddarmozzarellaSwissparmesan

soft cheeses

Light Blue/Milk• ricotta

cottage cheese

processed cheeses

• American

Yogurt*All yogurt

• Fat-freelow fatreduced fatwhole milk yogurt

*Selection Tips

Choose fat-free or low-fat milk, yogurt, and cheese. If you choose milk or yogurt that is not fat-free, or cheese that is not low-fat, the fat in the product counts as part of the discretionary calorie allowance. If sweetened milk products are chosen (flavored milk, yogurt, drinkable yogurt, desserts), the added sugars also count as part of the discretionary calorie allowance. For those who are lactose intolerant, lactose-free and lower-lactose products are available. These include hard cheeses and yogurt. Also, enzyme preparations can be added to milk to lower the lactose content. Calcium-fortified foods and beverages such as soy beverages or orange juice may provide calcium, but may not provide the other nutrients found in milk and milk products.

Purple/Meat-Bean

Purple/Meat-Beans• What foods are included in the meat, poultry, fish, dry beans, eggs, and nuts (meat & beans) group?

• All foods made from meat, poultry, fish, dry beans or peas, eggs, nuts, and seeds are considered part of this group. Dry beans and peas are part of this group as well as the vegetable group. For more information on dry beans and peas click here.

Most meat and poultry choices should be lean or low-fat. Fish, nuts, and seeds contain healthy oils, so choose these foods frequently instead of meat or poultry. (See Why is it important to include fish, nuts, and seeds?)

Some commonly eaten choices in the Meat and Beans group, with selection tips, are:

 What's in the Meat & Beans Group?  How much is needed?  What counts as an ounce?  Nutrients and health implications  Tips for making wise choices  Vegetarian Choices  Grains  Vegetables  Fruits  Milk  Meat & Beans  Oils  Discretionary Calories  Physical Activity

• •

Purple/Meat-Beans• Meats*

• Lean cuts of:

• beefhamlambporkveal

Game meats:

• bisonrabbitvenison

Lean ground meats:

• beefporklamb

Lean luncheon meatsOrgan meats:

• liver

• giblets

Purple/Meat-Beans

• Poultry*

• chickenduckgooseturkeyground chicken and turkey

Eggs*

• chicken eggsduck eggs

Purple/Meat-Beans• Dry beans and peas:

• black beansblack-eyed peaschickpeas (garbanzo beans)falafelkidney beanslentilslima beans (mature)navy beanspinto beanssoy beanssplit peastofu (bean curd made from soy beans)white beans

bean burgers:

• garden burgersveggie burgers

tempehtexturized vegetable protein (TVP)

Purple/Meat-Beans

• Nuts & seeds*• almonds

cashewshazelnuts (filberts)mixed nutspeanutspeanut butterpecanspistachiospumpkin seedssesame seedssunflower seedswalnuts

Purple/Meat-Beans• Fish*

• Finfish such as:

• catfishcodflounderhaddockhalibutherringmackerelpollockporgysalmonsea basssnapperswordfishtrouttuna

Purple/Meat-Beans• Shellfish such as:

• clamscrabcrayfishlobstermusselsoctopusoystersscallopssquid (calamari)shrimp

Canned fish such as:

• anchoviesclamstunasardines

Purple/Meat-Beans• *Selection Tips

Choose lean or low-fat meat and poultry. If higher fat choices are made, such as regular ground beef (75 to 80% lean) or chicken with skin, the fat in the product counts as part of the discretionary calorie allowance. Click here for more details on discretionary calories. If solid fat is added in cooking, such as frying chicken in shortening or frying eggs in butter or stick margarine, this also counts as part of the discretionary calorie allowance. Click here for more details on discretionary calories. Select fish rich in omega-3 fatty acids, such as salmon, trout, and herring, more often (See Why is it important to include fish, nuts, and seeds?). Liver and other organ meats are high in cholesterol. Egg yolks are also high in cholesterol, but egg whites are cholesterol-free. Processed meats such as ham, sausage, frankfurters, and luncheon or deli meats have added sodium. Check the ingredient and Nutrition Facts label to help limit sodium intake. Fresh chicken, turkey, and pork that have been enhanced with a salt-containing solution also have added sodium. Check the product label for statements such as “self-basting” or “contains up to __% of __”, which mean that a sodium-containing solution has been added to the product. Sunflower seeds, almonds, and hazelnuts (filberts) are the richest sources of vitamin E in this food group. To help meet vitamin E recommendations, make these your nut and seed choices more often.

Physical Activity

Physical Activity• Physical activity simply means movement of the body that uses energy. Walking, gardening, briskly pushing a

baby stroller, climbing the stairs, playing soccer, or dancing the night away are all good examples of being active. For health benefits, physical activity should be moderate or vigorous and add up to at least 30 minutes a day.

Moderate physical activities include: • Walking briskly (about 3 ½ miles per hour) • Hiking • Gardening/yard work • Dancing • Golf (walking and carrying clubs) • Bicycling (less than 10 miles per hour) • Weight training (general light workout) • Vigorous physical activities include: • Running/jogging (5 miles per hour) • Bicycling (more than 10 miles per hour) • Swimming (freestyle laps) • Aerobics • Walking very fast (4 ½ miles per hour) • Heavy yard work, such as chopping wood • Weight lifting (vigorous effort) • Basketball (competitive) • Some physical activities are not intense enough to help you meet the recommendations. Although you are

moving, these activities do not increase your heart rate, so you should not count these towards the 30 or more minutes a day that you should strive for. These include walking at a casual pace, such as while grocery shopping, and doing light household chores.

NUTRITION

• The ability of cells, especially those of the liver, to convert one type of molecules to another is truly remarkable– These interconversions allow the body to

use the wide range of chemicals found in foods and to adjust to varying food intakes

• But there are limits to these conversions:– At least 45-50 molecules, called essential nutrients,

cannot be made by the body and so must be provided by the diet

CARBOHYDRATESDietary Sources

• Except for milk sugar (lactose) and small amounts of glycogen found in meats, all the carbohydrates we ingest are derived from plants

• Sugars (monosaccharides and disaccharides) come from fruits, sugar cane, sugar beets, honey, and milk

• Polysaccharide starch is found in grains, legumes, and root vegetables

• Cellulose, a polysaccharide plentiful in most vegetables, is not digested by humans but provides roughage, or fiber, which increases the bulk of the stool and facilitates defecation

CARBOHYDRATESUses in the Body

• Glucose (monosaccharide) is the carbohydrate molecule ultimately used by the body as fuel to make ATP– Carbohydrate digestion also yields fructose and

galactose, but these monosaccharides are converted to glucose by the liver before they enter the general circulation

• Any glucose in excess of what the body needs for ATP synthesis is converted to glycogen or fat and stored for later use

• Pentose (monosaccharides) are used to synthesize nucleic acids

CARBOHYDRATESDietary Requirements

• The current recommendation is 125-175 grams of carbohydrates daily with the emphasis on complex carbohydrates (whole grains and vegetables)– When less than 50 grams per day is consumed,

tissue proteins and fats are used for energy fuel• Starchy foods and milk have many valuable

nutrients, such as vitamins and minerals– Refined carbohydrates (sugary foods and soft drinks)

provide energy sources only—the term “empty calories” is commonly used to describe such food

• Excess stored as fat (obesity)

LIPIDSDietary Sources

• The most common dietary lipids are the neutral fats, triglycerides or triacylglycerols, which occur as saturated fats and unsaturated fats– Compounds of higher fatty acids (molecular mass: e.g., oleic) with

glycerol– They are the common fats of animal and plant tissue – Known as oils when liquid

• Saturated fats (single bonds): animal products such as meat and dairy foods and in a few plant products such as coconut

• Unsaturated fats are present in seeds, nuts, and most vegetable oils

• Fats are digested to fatty acids and monoglycerides and then reconverted to triglycerides for transport in the lymph

• Cholesterol is another dietary lipid that is found in egg yolk, meats, and milk products

LIPIDS

LIPIDSDietary Sources

• Although the liver is adapt at converting one fatty acid to another, it cannot synthesize linoleic or linolenic acids– These are essential fatty acids that must

be ingested• Found in most vegetable oils

LIPIDSUses in the Body

• Dietary fats are essential as the major source of fuel for hepatocytes (liver cell) and skeletal muscle, for absorption of fat-soluble vitamins, and as components (phospholipids) of the myelin sheaths and cellular membranes of the body

LIPIDS

LIPIDSUses in the Body

• Fatty deposits in adipose tissue provide:– 1. A protective cushion around body organs– 2. An insulating layer beneath the skin– 3. An easy-to-store concentrated source of

energy fuel

LIPIDSUses in the Body

• Unlike neutral fats, cholesterol is not used for energy:– It is important as a stabilizing component

of plasma membranes and is the precursor from which bile salts, steroid hormones, and other essential molecules are formed

LIPIDSDietary Requirements

• Represents over 40% of the calories in the typical American diet– Diet high in saturated fats and cholesterol may

contribute to cardiovascular disease

• American Heart Association suggest:– 1. Fats should represent 30% or less of total caloric

intake– 2. Saturated fats should be limited to 10% or less of

total fat intake– 3. Daily cholesterol intake should be no more than

200 mg (amount in one egg yolk)

Fat Substitutes

• In an attempt to reduce fat intake without losing fat’s appetizing aspects, many people have turned to fat substitutes or foods prepared with them:– Perhaps the oldest fat substitute is air (beaten into a

product to make it fluffy)• Soft ice cream

• Most fat substitutes have two drawbacks:– 1. They don’t stand up to the intense heat needed to

fry foods– 2. They do not taste nearly as good as the real fat

PROTEINSDietary Sources

• Animal products contain the highest-quality proteins, those with the greatest amount and best ratio of essential amino acids

– Proteins in eggs, milk, and most meats are considered to be complete proteins that meet all the body’s amino acid requirements for tissue maintenance and growth

• Legumes (beans and peas), nuts, and cereals are protein-rich but their proteins are nutritionally incomplete because they are low in one or more of the essential amino acids

– Leafy green vegetables are well balanced in all essential amino acids except methionine, but contain only small amounts of protein

• Strict vegetarians must carefully plan their diets to obtain all the essential amino acids and prevent protein malnutrition

– When cereal grains and legumes (Mexican restaurant:rice and beans) are ingested together they provide all the essential amino acids

ESSENTIAL AMINO ACIDS

PROTEINSUses in the Body

• Proteins are important as structural materials of the body (keratin, collagen and elastin in connective tissue, and muscle proteins), enzymes, and hormones

• Whether amino acids are used to synthesize new proteins or are burned for energy depends on a number of factors:– 1.The all-or-none rule:

• All amino acids needed to make a particular protein must be present in a cell at the same time and in sufficient amounts for the protein to be made

• If one is missing, the protein cannot be made• Because essential amino acids cannot be stored, those not used

immediately to build proteins are oxidized for energy or converted to carbohydrates or fats

– 2.Adequacy of caloric intake:• For optimal protein synthesis the diet needs sufficient carbohydrate or fat

calories for ATP production• When it doesn’t dietary and tissue proteins are used fro energy

PROTEINSUses in the Body

– 3.Nitrogen balance:• In healthy adults the rate of protein synthesis equals the rate of protein

breakdown and loss– The body is in nitrogen balance when the amount of nitrogen ingested in proteins

is equal to the amount lost in urine and feces– Positive nitrogen balance: amount of protein being incorporated into tissue is

greater than the amount being broken down and used for energy» Growing children» Pregnant women» Tissue repair following injury or illness

– Negative nitrogen balance: protein breakdown for energy exceeds the amount of protein being incorporated into tissues

» Physical stress» Emotional stress» During infection, injury, burns» When quality of dietary protein is poor» Starvation

– 4.Hormonal controls:• Anabolic hormones accelerate protein synthesis and growth• The effects of these hormones vary continually throughout life

PROTEINSDietary Requirements

• Besides supplying essential amino acids, dietary proteins furnish the raw materials for making nonessential amino acids and various nonprotein nitrogen-containing substances

• The amount of protein a person needs reflects his or her age, size, metabolic rate, and current state of nitrogen balance– Nutritionists recommend a daily intake of 0.8 g per

kilogram of body weight (0.3 ounces per 2.2 pounds)– Most Americans eat far more protein than they

need

VITAMINS

• Vitamins are potent organic compounds needed in minute (small) amounts for growth and good health– Unlike other organic nutrients, vitamins are not used for

energy and do not serve as building blocks, but they are crucial in helping the body use those nutrients that do

• Most function as coenzymes or parts of coenzymes– Act with an enzyme to accomplish a particular chemical

task• Example: B vitamins riboflavin and niacin act as coenzymes in the

oxidation of glucose for energy

• Without vitamins, all the carbohydrates, proteins, and fats we eat would be useless

VITAMINS

• Most vitamins are not made in the body– They must be taken in via foods or vitamin supplements:

• Exceptions:– Vitamin D made in the skin– Vitamin K synthesized by intestinal bacteria– Body can convert beta-carotene (provitamin), the orange pigment in

carrots and other foods, to vitamin A

• Found in all major foods, but no one food contains all the required vitamins– Thus, a balanced diet is the best way to ensure a full vitamin

complement• Were given a letter designation that indicated the

order of their discovery– Today, a more chemical descriptive name has been

assigned

VITAMINS

• Water-soluble vitamins (B complex vitamins and vitamin C) are absorbed along with water from the gastrointestinal tract:– Exception: vitamin B12, which must bind to gastric intrinsic factor

(also needed to produce mature erythrocytes) to be absorbed• The only stomach function essential for life• Gastrectomy (stomach removal): vitamin B12 administered by

injection

• Because only insignificant amounts of water-soluble vitamins are stored in the body, any ingested amounts not used within an hour or so are excreted in urine– Few conditions resulting from excessive levels of these vitamins

(hypervitaminosis) are known

VITAMINS

• Fat-soluble vitamins (A, D, E, and K) bind to ingested lipids and are absorbed along with their digestion products– Anything that interferes with fat absorption also interferes

with the intake of fat-soluble vitamins• Except for vitamin K, fat-soluble vitamins are stored in the

body:– Fat-soluble vitamin toxicity (hypervitaminosis) has been documented

» Vitamin A: nausea, vomiting, anorexia (loss of appetite), headache, hair loss, bone and joint pain, bone fragility, enlargement of liver and spleen

» Vitamin D: toxic, vomiting, diarrhea, fatigue, weight loss, hypercalcemia (excess calcium in blood) and calcification of soft tissue, irreversible cardiac and renal damage

» Vitamin E: slow wound healing, decreased platelet adhesion, increased clotting time

» Vitamin K: not known because not stored in appreciable amounts

VITAMINS

• Metabolism uses oxygen, and during these reactions some potentially harmful free radicals are generated– Vitamins A, C, and E are antioxidants that

disarm tissue-damaging free radicals and thereby appear to have anticancer effects

• Good sources of A and C:– Broccoli, cabbage, cauliflower, and brussels sprouts

MINERALS• The body requires moderate amounts of seven minerals (calcium,

phosphorus, potassium, sulfur, sodium, chlorine, magnesium) and trace amounts of about a dozen (fluorine, cobalt, chromium, copper, iodine, iron, manganese, selenium, zinc) others that are used by the body to add strength to structures or to act as ions in the blood and cells

• Not used for fuel but work with other nutrients to ensure a smoothly functioning body

• Incorporation of minerals into structures give added strength:– Calcium, phosphorus, and magnesium salts harden the teeth and strengthen

the skeleton– Most are ionized in body fluids or bound to organic compounds to form

phospholipids (lipid portion of cell membrane), hormones, enzymes, and other functional proteins (Fe bound to heme)

– Sodium and chloride ions are the major electrolytes in blood• A fine balance between uptake and excretion is crucial for retaining

needed amounts of minerals while preventing toxic overload• The most mineral rich foods are vegetables, legumes, milk, and some

meats

METABOLISM

• Once inside body cells, nutrients become involved in an incredible variety of biochemical reactions known as metabolism

• Overview of Metabolic Processes:– Anabolism (building up) is the general term for all

reactions in which larger molecules or structures are built from smaller ones

• Example: synthesis of proteins from amino acids

– Catabolism degradation, tearing down) refers to all processes that break down complex structures to simpler ones

• Example: hydrolysis of food

The three stages of metabolism of energy-containing nutrients in the body

METABOLISM• In oxidation-reduction reactions one substance is oxidized and

loses energy by losing electrons, while another substance is reduced and gains energy and electrons that are transferred from the oxidized substance:– Oxidation: always loses (or nearly loses) electrons as they move to (or

toward) a substances that more strongly attracts them• Loss of electrons or,• Gain of oxygen (when oxygen binds with other atoms the shared electrons

spend more time in oxygen’s vicinity; the molecule as a whole loses electrons) or,

• Loss of hydrogen atoms (electron goes with it; the molecule as a whole loses electrons)

• Essentially all oxidation of food involves the step-by-step removal of pairs of hydrogen atoms (pairs of electrons) from the substrate molecules, eventually leaving only carbon dioxide (CO2)

– Molecular oxygen (O2) is the final electron acceptor» It combines with the removed hydrogen atoms at the very end of the

process, to form water (H2O)

METABOLISM

• Whenever one substance loses electrons (oxidized), another substance gains electrons (reduced)– Oxidation and reduction are coupled reactions (oxidation-

reduction reactions—redox reactions)– The key understanding about redox reactions is that “oxidized”

substances lose energy and “reduced” substances gain energy as energy-rich electrons are transferred from the former to the latter

– As foods are oxidized, their energy is transferred to a “bucket brigade” of other molecules and ultimately to ADP to form energy-rich ATP

– Redox reactions are catalyzed by enzymes:• Dehydrogenases: catalyze removal of hydrogen• Oxidases: catalyze the transfer (acceptance) of oxygen

METABOLISM

• Although the enzyme catalyze the removal of hydrogen atoms to oxidize a substance, they cannot accept the hydrogen (hold on or bond to it)– Their coenzyme, however, act as hydrogen

(electron) acceptors, becoming reduced each time a substrate is oxidized

• Two very important coenzymes:– Nicotinamide adenine dinucleotide (NAD+)

» Based on niacin (a B vitamin)– Flavin adenine dinucleotide (FAD)

» Derived from riboflavin (a B vitamin)» Oxidized form

REDOX REACTION

• The oxidation of succinic acid to fumaric acid and the simultaneous reduction of FAD to FADH2, an example of a coupled redox reaction

Mechanisms of ATP Synthesis • Our cells use two mechanisms to

capture some of the energy liberated through oxidation-reduction reactions to make ATP:

– 1.Substrate-level phosphorylation occurs when high-energy phosphate groups are transferred directly from phosphorylated substrates (metabolic intermediates such as glyceraldehyde phosphate) to ADP

• Essentially, this process occurs because the high-energy bonds attaching the phosphate groups to the substrates are even more unstable than those in ATP

MECHANISM OF PHOSPHORYLATION

Sites of ATP formation during cellular respiration

Mechanisms of ATP Synthesis

• 2.Oxidative phosphorylation is carried out by electron transport, which occurs in the cristae of the mitochondria and couples the movement of substances across membranes to chemical reactions– An example of chemiosmotic process:

• Couple the movement of substances across membranes to chemical reactions

• Some of the energy released during the oxidation of food is used to pump protons (H+) across the cristae membrane into the intermembrane space

• This creates a steep diffusion gradient for protons across the membrane

• Then, when H+ does flow back across the membrane (through a membrane channel protein called ATP synthase), some of this gradient energy is captured and used to attach phosphate groups to ADP

MECHANISM OF PHOSPHORYLATION

Sites of ATP formation during cellular respiration

Carbohydrate Metabolism• Because all food carbohydrates are eventually transformed to

glucose, the story of carbohydrates metabolism is really of glucose metabolism

• Glucose enters the tissue cells by facilitated diffusion, a process that is greatly enhanced by insulin

• Immediately upon entry into the cell, glucose is phosphorylated to glucose-6-phosphate by transfer of a phosphate group to its sixth carbon during a coupled reaction with ATP– Glucose + ATP → glucose-6-PO4 + ADP

• Because glucose-6-phosphate is a different molecule from simple glucose, the reaction also keeps intracellular glucose levels low, maintaining a diffusion gradient for glucose entry

Carbohydrate Metabolism

• Glucose is catabolized via the reaction:

• C6H12O6 + 6O2 → 6H2O + 6CO2 + 36ATP + HEAT

• Glucose breakdown involves 3 pathways:

• 1.Glycolysis:color-coded light orange

• 2.The Krebs Cycle: color-coded pale-green

• 3.The electron transport chain and oxidative phosphorylation: color-coded violet

The three stages of metabolism of energy-containing nutrients in the body

Sites of ATP formation during cellular respiration

Glycolysis

• A series of ten steps where glucose is converted into two pyruvic acid molecules in the cytosol of cells

• Anaerobic process (does not use oxygen and occurs whether or not oxygen is present)

Glycolysis• Three major phases:• 1.Sugar activation:

– Glucose is phosphorylated and converted to fructose-6-phosphate, which is then phosphorylated again

• Yields frucrose-1,6-bisphosphate• These two reactions provide the

activation energy needed to prime the later stages of the pathway

• Energy investment phase: uses 2 ATP

• 2.Sugar cleavage:– Frucrose-1,6-bisphosphate is split

into 3-carbon fragments• Existing as one of two isomers:

– Glyceraldehyde 3-phosphate– Or– Bishydroxyacetone phospahte

Glycolysis• 3.Oxidation and ATP formation:

– Six steps with two major events• 1.Formation of NADH+H+

(Nicotinamide adenine dinucleotide)

• 2.Inorganic phosphate groups (Pi) are attached to each oxidized fragment by high-energy bonds

• Final Product:– Two molecules of pyruvic acid and

two molecules of reduced NAD+ (NADH + H+)

– Net gain of two ATP molecules per glucose molecule

• 4 ATPs are produced, but remember that 2 are consumed in phase 1

THREE MAJOR PHASES OF GLYCOLYSIS

Glycolysis• When oxygen is readily available, NADH

+ H+ delivers its burden of hydrogen atoms to the enzymes of the electron transport chain in the mitochondria, which deliver them to O2, forming water

• However, when oxygen is not present in sufficient amounts, as might occur during strenuous exercise, NADH + H+ unloads its hydrogen atoms back onto pyruvic acid, thus reducing it

– This addition of two hydrogen atoms to pyruvic acid yields lactic acid, some of which diffuses out of the cells and is transported to the liver (converting it to glucose and storing it or releasing it to the blood)

– When oxygen is again available, lactic acid is oxidized back to pyruvic acid and enters the aerobic pathways (Krebs cycle and electron transport chain within the mitochondria), and is completely oxidized to water and carbon dioxide

THREE MAJOR PHASES OF GLYCOLYSIS

Krebs Cycle• Occurs in the matrix (fluid portion) of the

mitochondria where the pyruvic acid is passed through a series of reactions that generate reduced electron carrier molecules, NADH + H+ and FADH2

• Fueled largely by pyruvic acid production during glycolysis and by fatty acids resulting from fat breakdown

• After pyruvic acid enters the mitochondria, it is converted to acetyl CoA (coenyzme A: sulfur containing coenzyme derived from pantothenic acid, a B vitamin) via three-step process

– 1.Decarboxylation: one of pyruvic acid’s carbons is removed and released as carbon dioxide gas (diffuses into the blood and is expelled by the lungs)

– 2.Oxidation: removal of hydrogen atoms which are picked up by NAD+ (Nicotinamide adenine dinucleotide)

– 3.Combination of the resulting acetic acid with coenzyme A to produce the final product, acetyl coenzyme A (acetyl CoA)

• Acetyl CoA enters the Krebs Cycle

Krebs (Citric Acid) Cycle

• Coenzyme A shuttles the 2-carbon acetic acid to an enzyme that condenses it with a 4-carbon acid called oxaloacetic acid to produce the 6 carbon citric acid– Because citric acid is the

first substrate of the cycle, biochemists prefer to call the Krebs cycle the citric acid cycle

Krebs (Citric Acid) Cycle• As the cycle moves through its

eight successive steps, the atoms of citric acid are rearranged to produce different intermediate molecules, most called keto acids

• At the end of the cycle, acetic acid has been totally disposed of and oxaloacetic acid, the pickup molecule, is regenerated

• Two decarboxylations and four oxidations occur:

– Products are 2CO2 molecules and 4 molecules of reduced coenzymes (3 NADH + H+ and 1 FADH2)(Nicotinamide adenine dinucleotide and Flavin adenine dinucleotide)

– Notice that it is the Kreb cycle reactions that produce the CO2 evolved during glucose oxidation

Krebs (Citric Acid) Cycle• Glycolysis: oxygen not used

– Two molecules of pyruvic acid– Two molecules of reduced NAD+

(NADH + H+)– Net gain of two ATP molecules per

glucose molecule• 4 ATPs are produced, but remember

that 2 are consumed in phase 1

• Krebs (Citric Acid) Cycle: oxygen not used:

– Two molecules of pyruvic acid enter• Six molecules of CO2

• Ten molecules of reduced coenzymes (removal of 10 hydrogen atoms)

– 8 NADH + H+

– 2 FADH2

• Two ATP

• Total at this point:– 6CO2

– 4ATP

KREBS CYCLE

Krebs (Citric Acid) Cycle

• Although the glycolytic pathway is exclusive to carbohydrate oxidation, breakdown products of carbohydrate, fats, and proteins can feed into the Krebs cycle to be oxidized for energy– Some Krebs cycle intermediates can be siphoned off

to make fatty acids and nonessential amino acids

• Thus the Krebs cycle, besides serving as the final common pathway for the oxidation of food fuels, is a source of building materials for anabolic reactions

Electron Transport Chain and Oxidative Phosphorylation

• Electron transport chain is the final catabolic reactions that occur on the mitochondrial cristae– Consumes oxygen– However, because the reduced coenzymes produced in the

Krebs cycle are the substrates for the electron transport chain, these pathways are coupled, and both phases are considered to be oxygen requiring (aerobic)

• Hydrogens removed during the oxidation of foods are combined with O2, and the energy released during those reactions is harnessed to attach Pi (inorganic phospahtes) groups to ADP – Process called oxidative phosphorylation

Electron Transport Chain and Oxidative Phosphorylation

• Most components of the electron transport chain are proteins that are bound to metal (Fe, S) atoms (cofactors):

– Part of the mitochondrial cristae– Cluster together to form major respiratory

enzyme complexes that are alternately reduced and oxidized by picking up electrons and passing them on to the next complex in the sequence

– The hydrogen atoms delivered to the electron transport chain by the reduced coenzymes are quickly split into protons (H+) plus electrons

– The electrons are shuttled along the crista membrane from one acceptor to the next

– The protons escape into the watery matrix– The electrons are delivered to an oxygen

atom creating oxygen (O-) ions– Strongly attract H+ (hydrogen

ions) and form water• Virtually all the water resulting from

glucose oxidation is formed during oxidative phosphorylation

HYPOTHETICAL MECHANISM OF OXIDATIVE PHOSPHORYLATION

ELECTRONIC ENERGY GRADIENT IN THE ELECTRON TRANSPORT CHAIN

Electron Transport Chain and Oxidative Phosphorylation

• Because NADH + H+ (Nicotinamide adenine dinucleotide) and FADH2 (Flavin adenine dinucleotide) are oxidized as they release their burden of picked-up hydrogen atoms, the net reaction for the electron transport chain is:

• Coenzyme-2H + ½O2 → coenzyme + H2O

– reduced coenzyme oxidized coenzyme

Electron Transport Chain and Oxidative Phosphorylation

• The transfer of electrons from NADH + H+ to oxygen releases large amounts of energy

• If hydrogen combined directly with molecular oxygen, the energy would be released in one big burst and most of it would be lost to the environment as heat

• Instead energy is released in many small steps as the electrons stream from one electron acceptor to the next

• Each successive carrier has a greater affinity for electrons than those preceding it

– Therefore, the electrons cascade downhill from NADH + H+ to progressively lower energy levels until they arte finally delivered to oxygen, which has the greatest affinity of all for electrons

Electron Transport Chain and Oxidative Phosphorylation

• As the protons take cascade they create an electric current, and ATP synthase harnesses this electrical energy to catalyze attachment of a Phosphate group to ADP to form ATP

Electron Transport Chain and Oxidative Phosphorylation

• Rotating structure of ATP synthase (like rotating water wheel) activates catalytic sites resulting in ADP joining with inorganic phosphate (Pi) producing ATP

ATP SYNTHASE

HOMEOSTATIC IMBALANCE

• Metabolic poisons binds to enzymes disrupting the metabolic pathways

Summary of ATP Production• Glycolysis: oxygen not used

– Two molecules of pyruvic acid– Two molecules of reduced NAD+ (NADH + H+)– Net gain of two ATP molecules per glucose

molecule• 4 ATPs are produced, but remember that 2 are

consumed in phase 1

• Krebs (Citric Acid) Cycle: oxygen not used– Two molecules of pyruvic acid enter

• Six molecules of CO2

• Ten molecules of reduced coenzymes (removal of 10 hydrogen atoms)

– 8 NADH + H+

– 2 FADH2

• Two ATP

• Total at this point:– 6CO2

– 4ATP• Oxidative phosphorylation:

– Every time NADH + H+ and FADH2 are produced, ATPs are formed

CELLULAR RESPIRATION

Glycogenesis and Glycogenolysis

• When more glucose is available than can be immediately oxidized, rising intracellular ATP concentrations eventually inhibit glucose catabolism and initiate processes that store glucose as either glycogen or fat

– Because the body can store much more fat than glycogen, fats account for 80-85% of stored energy

• Glycogenesis is the formation of glycogen, the animal storage form of glucose, that occurs when excess glucose is ingested

– Liver and skeletal muscle cells are most active in glycogen synthesis and storage

• Glycogenolysis is the breakdown of glycogen into individual glucose molecules that occurs when the blood sugar levels drop

GLYCOGENESIS AND

GLYCOGENOLYSIS

Gluconeogenesis

• Gluconeogenesis is the process of forming new glucose from noncarbohydrate molecules that occurs in the liver using glycerol and amino acids:– It takes place when dietary sources and glucose

reserves have been depleted and blood glucose levels are beginning to drop

– Protects the body, the nervous system on particular, from the damaging effects of low blood sugar (hypoglycemia) by ensuring that ATP synthesis can continue

LIPID METABOLISM

• Fats are the body’s most concentrated source of energy

• They contain little water, an the energy yield from fat catabolism is approximately twice that from either glucose or protein catabolism—9 kcal per gram of fat versus 4 kcal per gram of carbohydrate or protein

• Most products of fat digestion are transported in lymph in the form of fatty-protein droplets called chylomicrons– Eventually, the lipids in the chylomicrons are hydrolyzed by

plasma enzymes, and the resulting fatty acids and glycerol are taken up by body cells and processed in various ways

Oxidation of Glycerol and Fatty Acids

• Of the various lipids, only neutral fats are routinely oxidized for energy

• Neutral fats: consist of fatty acid chains and glycerol; also called triglycerides or triacylglycerols

– Commonly known as oils when liquid– Their catabolism involves the separate

oxidation of their two different building blocks: glycerol and fatty acid chains

• Most body cells easily convert glycerol to glyceraldehyde phosphate, a glycolysis intermediate that enters the Krebs cycle

• Beta oxidation: occurs in the mitochondria

– Is the first phase of fatty acid metabolism where fatty acid chains are split into two carbon acetic acid fragments and coenzymes are reduced forming acetyl CoA

» Which is picked up by oxaloacetic acid and enters the aerobic pathways to be oxidized to CO2 and H2O

– Beta refers to the fact that the 3rd carbon is oxidized and the cleavage is between the alpha and beta carbons

INITIAL PHASE OF LIPID OXIDATION

Lipolysis• Is the breakdown of stored fats into glycerol and fatty acids to be used

by the body for fuel:– Released to the blood, helping to ensure that body organs have continuous

access to fat fuels for aerobic respiration• The liver, cardiac muscle, and resting skeletal muscles actually prefer fatty acids as an

energy fuel

• When carbohydrate intake is inadequate, lipolysis is accelerated as the body attempts to fill the fuel gap with fats depending on the availability of oxaloacetic acid to act as the pickup molecule to help enter the Krebs Cycle

• When carbohydrates are deficient, oxaloacetic acid is converted to glucose (to fuel the brain)

– Without oxaloacetic acid, fat oxidation is incomplete resulting in ketones, which are released into the blood

• When they accumulate in the blood, ketoacidosis can result– pH drops– Disrupts heart activity and oxygen transport– Severe depression of nervous system– Common consequence of starvation, unwise dieting ( inadequate amounts of carbohydrates),

and diabetes mellitus– Coma and death

METABOLISM OF TRIGLYCERIDES

Lipogenesis

• Reversal of Lipolysis• Is the reformation of triglycerides from unused

glycerol and fatty acid chains for storage in the body– Glycerol and fatty acids not immediately needed for energy are

recombined into triglycerides and stored• About 50% ends up in subcutaneous tissue; the balance is stored in

other fat areas of the body

• Occurs when cellular ATP and glucose (easily converted to fat) levels are high

• Even if the diet is fat-poor, carbohydrate intake can provide all the raw materials needed to form neutral fats

METABOLISM OF TRIGLYCERIDES

PROTEIN METABOLISM

• Proteins have a limited life span and must be broken down and replaced before they begin to deteriorate– Newly ingested amino acids transported in the

blood are taken up by cells by active transport processes and used to replace tissue proteins

• When more protein is ingested than is needed for these anabolic purposes, amino acids are oxidized for energy or converted to fat

Oxidation of Amino Acids

• Before amino acids can be oxidized for energy, they must be deaminated, that is, their amine group (NH2) must be removed:– The resulting molecule is

then converted to pyruvic acid or to one of the keto acid intermediates in the Krebs cycle

– The key molecule in these conversions is the nonessential amino acid glutamic acid

Transamination

• Transamination is the process of transferring an amine group to alpha-ketoglutaric acid (a Krebs cycle keto acid) to make glutamic acid– The original amino

acid becomes a keto acid (oxygen atom where the amine group formerly was)

Oxidative Deamination

• Occurs in the liver and removes the amine group of glutamic acid as ammonia (NH3) and regenerates alpha-ketoglutaric acid:– The NH3 (toxic to the body)

combines with CO2 yielding urea and water

• The urea is released to the blood and excreted in the urine

• This mechanism rids the body not only of NH3 produced during oxidative deamination, but also of bloodborne NH3 produced by intestinal bacteria

Keto Acid Modification

• The goal of amino acid degradation is to produce molecules that can be either oxidized in the Krebs cycle or converted to glucose

• Keto acid modification is used to produce molecules that can be oxidized in the Krebs cycle or converted to glucose from keto acids produced through transamination– Most important of these

metabolites are pyruvic acid, acetyl CoA, alpha-ketoglutaric acid, and oxaloacetic acid

TRANSAMINATION

Protein Synthesis• Amino acids are the most important anabolic nutrients:

– Protein structures– Enzymes

• Occurs in the ribosomes, where cytoplasmic enzymes oversee the formation of peptide bonds linking the amino acids together into protein polymers

• The amount and type of protein synthesized are precisely controlled by hormones (growth, thyroxine, sex hormones, etc.)

• You do not need to ingest extreme amounts of proteins because nonessential amino acids are easily formed by removing keto acids from the Krebs cycle and transferring amine groups to them

– Most of these transformations occur in the liver, which provides nearly all the nonessential amino acids needed to produce the relatively small amount of protein that the body synthesizes each day

– However, a complete set of amino acids must be present for protein synthesis to take place, so all essential amino acids must be provided by the diet

• If some are not, the rest are oxidized for energy even though they may be needed for anabolism

– Negative nitrogen balance results because body protein is broken down to supply the essential amino acids needed

METABOLISM

• The body exists in a dynamic catabolic-anabolic state, where substances are continually being broken down and rebuilt

• The body nutrient pools—amino acids, carbohydrates, and fat stores—can be drawn on to meet its varying needs– These pools are

interconvertible because their pathways are linked by key intermediates

NUTRIENT POOL

METABOLISM

• The liver, adipose tissue, and skeletal muscles are the primary effector organs determining the amounts and direction of the conversions

PATHWAYS OF INTERCONVERSION OF CARBOHYDRATES, FATS, AND PROTEINS

Absorptive and Postabsorptive States

• Absorptive state is the time during and shortly after eating when nutrients are moving into the blood from the GI tract:– Anabolism exceeds catabolism– Absorbed monosaccharides are delivered directly to the liver

where they are converted into glucose and either used by the cells of the body, stored as glycogen, or converted into fats to be stored

– Triglycerides are either used for anabolic purposes or stored in adipose tissue

– Amino acids are delivered to the liver, which delaminates some and uses others to make plasma proteins, but most remain in the blood to be distributed to body cells

MAJOR EVENTS AND PRINCIPAL METABOLIC PATHWAYS OF THE ABSORPTIVE STATE

Hormonal Control

• Insulin directs all events of the absorptive state

EFFECTS OF INSULIN ON METABOLISM

Postabsorptive State

• Postabsorptive state is the period when the GI tract is empty and energy resources are supplied by the body reserves:– Glycogenolysis: breaking down of glycogen

• Source of blood glucose include glycogen in the liver, skeletal muscle cells, adipose tissues, and cellular proteins

– Lipolysis in adipose tissues and the liver• Adipose tissue and liver cells produce glycerol by lipolysis,

and the liver converts the glycerol to glucose– Catabolism of cellular protein:

• Cellular amino acids are deaminated and converted to glucose in the liver

– During extended periods of fasting the kidneys are also capable of gluconeogenesis

MAJOR EVENTS AND PRINCIPAL METABOLIC PATHWAYS OF THE POSTABSORPTIVE STATE

Glucose Sparing

• Glucose sparing is the increased use of noncarbohydrate fuel molecules (especially triglycerides) for energy to conserve glucose during times of fasting

• As the body progresses from absorptive to postabsorptive state, the brain continues to take its share of blood glucose; but virtually every other organ switches to fatty acids as its major energy source, thus sparing glucose for the brain

Hormonal and Neural control

• The sympathetic nervous system and several hormones interact to control the postabsorptive state

INFLUENCE OF GLUCAGON ON PLASMA GLUCOSE CONCENTRATION

LIPIDS• Any one of a group of fats or fatlike substances, characterized

by their insolubility in water and solubility in fat solvents such as alcohol, ether, and chloroform

• Term is descriptive rather than a chemical name such as protein or carbohydrate

• Includes:– True fats (esters of fatty acids and glycerol)– Lipoids:

• Phospholipids: lipid with phosphorus (a diglyceride containing phosphorus) • Cerebrosides: lipid in nerves• Waxes:

– Sterols:• Cholesterol: C27H45OH, a monohydric alcohol (having a single replaceable

hydrogen atom)– Sterol widely distributed in animal tissues

• Ergosterol: fat in the cell membrane of fungi– Role similar to that of cholesterol in human cells

Triglyceride (Fats)

Phospholipids

Phospholipids

Cholesterol

Steroids

Cholesterol

Sterol/Cholesterol

Cholesterol

Development of various Steroids

Cholesterol

Metabolic Role of the Liver

• The liver processes nearly every class of nutrient and plays a major role in regulating plasma cholesterol levels

• The hepatocytes carry out over 500 metabolic functions

Cholesterol Metabolism

• Cholesterol is not used as an energy source:– Cholesterol serves as the structural basis for bile

salts, steroid hormones, vitamin D; as a component of the plasma membrane; and as a signaling molecule in embryonic development

– About 85% of cholesterol (15% in our diet) is made in the liver from acetyl CoA and other body cells (particularly intestinal cells), and is lost from the body in bile salts in feces

Cholesterol Transport

• Triglycerides (neutral fats) and cholesterol are insoluble in water and must be transported in the body bound to small lipid-protein complexes called lipoproteins

• In general, the higher the percentage of lipid in the lipoprotein, the lower its density

• The greater the proportion of protein, the higher its density

Cholesterol Transport

• HDLs: high-density lipoproteins (higher protein)

• LDLs: low-density lipoproteins (higher lipids)

• VLDLs: very low density lipoproteins

• Chylomicrons: transport absorbed lipids from the GI tract, are a separate class and have the lowest density

APPROXIMATE COMPOSITION OF LIPOPROTEINS THAT TRANSPORT LIPIDS IN

BODY FLUIDS

Cholesterol Transport

• VLDLs is primarily produced in the liver– Transports triglycerides from the liver to the peripheral tissues,

but mostly to adipose tissues– Triglycerides are unloaded, the VLDL residues are converted to

LDLs

• LDLs: are cholesterol rich– Transports cholesterol to peripheral tissues, making it available

to the tissue cells for membrane or hormone synthesis and for storage for later use

– Regulate cholesterol synthesis in the tissue cells

• HDL: rich in phospholipids– Transport excess cholesterol from peripheral tissues to the liver,

where it is broken down and becomes part of bile

Cholesterol

Cholesterol Counts

• Total Cholesterol: above 200mg/100ml blood– Linked to risk of atherosclerosis (clogs the arteries

and causes strokes and heart attacks)– Not enough to simply measure total cholesterol– The form in which cholesterol is transported in the

blood is more important clinically• HDLs:

– High levels are considered good because the transported cholesterol is destined for degradation

» 35-60: okay» Above 60: protects against heart disease

• LDLs:– High levels are considered bad because potentially lethal

deposits are laid down in the artery walls

Cholesterol Levels

Factors Regulating Plasma Cholesterol Levels

• A negative feedback loop partially adjusts the amount of cholesterol produced by the liver according to cholesterol in the diet:– Severe restriction of dietary cholesterol does not lead to a steep

reduction in plasma cholesterol levels since the liver produces a certain amount of cholesterol even when dietary intake is excessive (NO MJAOR NEGATIVE FEEDBACK MECHANISM)

• Saturated fatty acids stimulate liver synthesis of cholesterol and inhibit its excretion from the body– Thus, moderate decreases in intake of saturated fats (animal

fats and coconut oil) can reduce cholesterol levels

Factors Regulating Plasma Cholesterol Levels

• In contrast, unsaturated fatty acids (most vegetable oils) enhance excretion of cholesterol from the body and its catabolism to bile salts, thereby reducing total cholesterol levels– Exception:

• Healthy oils that have been hardened by hydrogenation to make them more solid

– Hydrogenation is a process of changing an unsaturated fat to a solid saturated fat by the addition of hydrogen in the presence of a catalyst

• Hydrogenation changes the fatty acids in the oil to trans fatty acids– Cause serum changes worse than those caused by saturated fats

» Trans fatty acids cause a greater increase in LDL levels and a greater reduction in HDL levels than saturated fatty acids (producing the unhealthiest ratio of total cholesterol to HDL)

Factors Regulating Plasma Cholesterol Levels

• The unsaturated omega-3 fatty acids found in certain fish lowers the proportions of both saturated fats and cholesterol

• The omega-3 fatty acids (linoleic and arachidonic) have a powerful antiarrhythmic effect on the heart and also make blood platelets less sticky, thus helping prevent spontaneous clotting that can block blood vessels– Lowers blood pressure even in nonhypertensive

people

Omega-3

Omega-3/6

• It is very important to maintain a balance between omega-3 and omega-6 fatty acids in the diet. Omega-3 fatty acids help reduce inflammation and most omega-6 fatty acids tend to promote inflammation. An inappropriate balance of these essential fatty acids contributes to the development of disease while a proper balance helps maintain and even improve health. A healthy diet should consist of roughly one to four times more omega-6 fatty acids than omega-3 fatty acids. The typical American diet tends to contain 11 to 30 times more omega-6 fatty acids than omega-3 fatty acids and many researchers believe this imbalance is a significant factor in the rising rate of inflammatory disorders in the United States.

Omega-3/6

• In contrast, however, the Mediterranean diet consists of a healthier balance between omega-3 and omega-6 fatty acids and many studies have shown that people who follow this diet are less likely to develop heart disease. The Mediterranean diet does not include much meat (which is high in omega-6 fatty acids) and emphasizes foods rich in omega-3 fatty acids including whole grains, fresh fruits and vegetables, fish, olive oil, garlic, as well as moderate wine consumption.

Omega-3

• Eat a variety of (preferably fatty) fish at least twice a week. Include oils and foods rich in alpha-linolenic acid (flaxseed, canola and soybean oils; flaxseed and walnuts).

Omega-3• Oily fish (oil-rich fish, pelagic fish) are those fish which have oils

throughout the fillet and in the belly cavity around the gut, rather than only in the liver like white fish. Oily fish fillets may contain up to 30 percent oil, although this figure varies both within and between species. Oily fish generally swim in mid-waters or near the surface (the pelagic zone).

• Oily fish are a good source of Vitamins A and D as well as being rich in Omega 3 fatty acids. For this reason the consumption of oily fish has been identified as more beneficial to humans than white fish. Amongst other benefits, studies suggest that the Omega 3 fatty acids in oily fish may help sufferers of depression, reduce the likelihood of heart disease and improve inflammatory conditions such as arthritis.

Omega-3/6

• The main sources of omega-6 fatty acids are vegetable oils such as corn oil and soy oil that contain a high proportion of linoleic acid. Omega-3 acids are found in flaxseed oil, walnut oil, and marine plankton and fatty fish. The main component of flaxseed and walnut oils is alpha-linolenic acid while the predominant fatty acids found in fatty fish and fish oils are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The most beneficial and active of these fatty acids are EPA and DHA. Alpha-linolenic acid can be converted to EPA and DHA in the body, but the conversion is quite inefficient especially in older people. [1, 2]

Omega-3

Omega-3

Factors Regulating Plasma Cholesterol Levels

• In those with moderate to high cholesterol levels, replacing half of the lipid-and cholesterol-rich animal proteins in the diet with soy protein lowers cholesterol levels

• Smoking, coffee drinking, and stress increase LDL levels

• Regular aerobic exercise appears to reduce LDL levels and increase HDL levels

Cholesterol Levels• Studies indicate:

– That cholesterol levels below 190 for males and 178 for females may be equally devastating because they may enhance the risk of “bleeding” strokes and death from cerebral hemorrhage

– Almost half of those who get heart disease have normal cholesterol levels

• Others with poor lipid levels remain free of heart disease

• Although most Americans would probably benefit from reducing their intake of saturated fats and cholesterol-rich foods, at least for now, the moderate approach to cholesterol control may be the wisest

ENERGY BALANCE

• First Law of Thermodynamics: energy can be neither created nor destroyed—only converted from one form to another

• A dynamic exists within the body between the energy intake and energy output– Energy intake is the energy liberated during food

oxidation– Energy output includes energy lost as heat, energy

used to do work, and energy that is stored as fat or glycogen

ENERGY BALANCE

• Regulation of Food Intake:– Hypothalamus: releases several peptides that

influence feeding behavior• Orexins: appetite enhancer• Neuropeptide Y: causes us to crave carbohydrates• Galanin: causes us to crave for fats• GLP-1 (glucagon-like peptide) and serotonin make us

feel full and satisfied

– When energy intake and energy output are balanced weight remains stable; when not balanced weight is either lost or gained

ENERGY BALANCE• Current theories of how feeding behavior and hunger are related focus on one

or more of five factors: All of these factors appear to operate through feedback signals to the feeding centers of the brain

– Neural signals from the digestive system• Vagus nerve fibers carry on a two-way connection between the gut and brain

– Response to presence of carbohydrates and proteins

– Bloodborne signals related to body energy stores• Levels of glucose, amino acids, and fatty acids

– Hormones:• Insulin; pancreas

– Decreases blood glucose level• Leptin released by fat cells:

– Influences the storage of fat• Glucagon: pancreas

– Increases blood glucose level• Epinephrine: adrenal gland

– Response to stress– Triggers hunger

• Cholecystokinin: intestinal hormone secreted during food digestion– Depresses hunger– More in elderly people

– Body temperature• Increased body temperature may inhibit eating

– Psychological factors

FEEDING BEHAVIOR AND SATIETY CONTROLS

Metabolic Rate and Heat Production

• The body’s rate of energy output is called the metabolic rate, which is the total heat produced by all the chemical reactions and mechanical work of the body

– Measured by directly by a calorimeter: heat liberated by the body is absorbed by water circulating around a chamber

• Rise in temperature is related to heat produced by the body

– Measured indirectly by a respirometer

• Measures oxygen consumption, which is proportional to heat production

• Each liter of oxygen used, the body produces about 4.8 kcal of heat

INDIRECT MEASUREMENT OF METABOLIC RATE BY RESPIROMETRY

Metabolic Rate and Heat Production

• The basal metabolic rate (BMR) reflects the energy the body needs to perform only its most essential activities, such as breathing and maintaining resting levels of organ function

– This measurement is NOT the lowest metabolic state of the body• This situation occurs during sleep, when the skeletal muscles are completely relaxed

– Reported in kilocalories per square meter of body surface per hour (kcal/m2/h)• You can approximate your BMR by multiplying weight in kilograms (2.2 pounds=1Kg)

by 1 if you are male and 0.9 if you are female– 70-Kg male (154 lbs) has a BMR of 70 kcal/h

• Factors influencing BMR include body surface area, age, gender, stress, and hormones:

– Critical factor is body surface area: This reflects the fact that as the ratio of body surface area to body volume increases, heat loss to the environment increases and the metabolic rate must be higher to replace the lost heat

• Hence, if two people weigh the same, the taller and thinner person will have the higher BMR

– Younger: higher MBR• Large amounts of energy for growth

Metabolic Rate and Heat Production

• Factors influencing BMR include body surface area, age, gender, stress, and hormones

• Gender: higher in males• Males: more muscle which is very active metabolically• Females: more fat which is metabolically sluggish

– Stress: physical or emotional increases BMR– Hormones:

• Norepinephrine and epinephrine (adrenal medulla) increase BMR• Thyroxine: most important hormonal factor in determining BMR

– Direct affect on most body cells (except brain cells) is to increase O2 consumption, presumably by accelerating the use of ATP to operate the sodium-potassium pump

– As ATP reserves decline, cellular respiration accelerates» Thus, the more thyroxine produced, the higher BMR

Metabolic Rate and Heat Production

• The total metabolic rate (TMR) is the rate of kilocalorie consumption needed to fuel all ongoing activities both involuntary and voluntary

Regulation of Body Temperature

• Body temperature regulation represents a balance between heat production and heat loss:

– The body’s core (organs within the skull, thoracic and abdominal cavities) has the highest temperature and its shell (the skin) has the lowest temperature in most circumstances

• Although all body tissues produce heat, those most active metabolically produce the greatest amounts

• Body temperature is usually maintained within the range 35.6-37.80C (96-1000F)

– 36.20C (98.60F) being the average

• Most adults go into convulsions when body temperature reaches 410C (1060F)

– 430C (1100F) appears to be the absolute limit for life

HEAT BALANCE

Core and Shell Temperatures

• Different body regions have different resting temperatures:– Core: organs within the skull and the thoracic and

abdominal cavities• Higher temperature

– Shell: essentially the skin• Lower temperature in most circumstances

– Varies when body is regulating temperature

• Of the two body sites used routinely to obtain body temperature clinically, the rectum typically has a temperature about 0.40C (0.70F) higher than the mouth and is a better indicator of core temperature

Mechanism of Heat Exchange

• Heat always flows down its concentration gradient from a warmer region to a cooler region– Radiation is the loss of heat in the form of infrared waves

(thermal energy)• 50% of body heat is lost

– Conduction is the transfer of heat from a warmer object to a cooler one when the two are in direct contact with each other

– Convection occurs when the warm air surrounding the body expands and rises and is replaced by cooler air molecules

– Evaporation removes large amounts of body heat when water absorbs heat before vaporizing

HEAT EXCHANGE

Role of the Hypothalamus

• The brain’s main integrating center for thermoregulation, containing the heat-loss center and the heat-promoting center

Heat-Promoting Mechanisms• Heat-promoting mechanisms are triggered when the external

temperature is low, or blood temperature falls and the heat-promoting center is activated

– Vasoconstriction of cutaneous blood vessels:• Blood is restricted to deep body areas and largely bypasses the skin

– Skin is separated from deeper organs by a layer of insulating subcutaneous (fatty) tissue– If restriction is extended, skin cells deprived of oxygen and nutrients begin to die (frostbite in

cold weather)

– Increase in metabolic rate:• Cold stimulates the release of norepinephrine which elevates the metabolic rate

– Shivering:• Involuntary shuddering contractions of muscles

– Increases body temperature because muscle activity produces large amounts of heat

– Enhanced thyroxine release:• Thyroid hormone increases metabolic rate

– Behavioral modifications:• Clothing• Drink warm liquids• Increased physical activity

MECHANISMS OF BODY TEMPERATURE REGULATION

Heat-Loss Mechanisms

• Protect the body from excessively high temperatures

• Whenever core body temperature rises above normal, the hypothalamus heat-promoting center is inhibited:– At the same time, the heat-loss center is activated

and so triggers one or both of the following:• Vasodilation of cutaneous blood vessels:

– allows the body to lose heat through radiation, conduction, and convection

• Enhanced sweating:– If the body is extremely overheated or if the environment is so

hot that heat cannot be lost by other means, evaporation becomes necessary

MECHANISMS OF BODY TEMPERATURE REGULATION

Heat Stroke/Heat Exhaustion • Hyperthermia: elevated body temperature

– Heat Stroke:• Normal heat loss processes become ineffective• Heat-control mechanisms are suspended, creating a vicious positive

feedback cycle• Increasing temperature increase the metabolic rate, which increases heat

production• Organ damage becomes a distinct possibility, including brain damage

– Heat exhaustion:• Often used to describe the heat-associated collapse of an individual during

or following vigorous physical activity– Evidenced by elevated body temperature and mental confusion and/or fainting

• Due primarily to dehydration and consequent low blood pressure• In contrast to heat stroke, heat-loss mechanisms are still functional• Can rapidly progress to heat stroke if the body is not cooled and rehydrated

promptly

Fever• Fever is controlled hyperthermia, usually resulting from an infection

somewhere in the body• Whatever the cause, white blood cells, injured tissue cells, and

macrophages release cytokines called pyrogens (fire starters), which act on the hypothalamus, causing release of prostaglandins

– The hypothalamus is reset to a higher-than-normal temperature, causing heat-promoting mechanisms to kick in:

• Vasoconstriction• Heat loss from body surfaces declines• Skin cools• Shivering begins to generate heat

– Temperature rises until it reaches the new setting, and then is maintained at that setting until natural body defenses or antibiotics reverse the disease process

– Temperature is reset to a lower (normal) level:• Heat-loss mechanisms swing into action• Sweating begins• Skin becomes flushed and warm

DEVELOPMENTAL ASPECTS OF NUTRITION AND METABOLISM

• Embryological– Good nutrition is essential in utero for the

growth of fetal tissues and brain– Inadequate calories during the first three

years of life, a time of brain growth, will lead to mental deficits or learning disorders

– Proteins are needed for muscle and bone growth, and calcium is required for strong bones

DEVELOPMENTAL ASPECTS OF NUTRITION AND METABOLISM

• Aging– By middle age and old age non-insulin-

dependent diabetes mellitus becomes a problem, especially in the obese

– Metabolic rate declines as we age– Muscle and bones deteriorate, and the

efficiency of the endocrine system decreases