nutrition. nutrients are constituents of food that provide energy & essential molecules...

NUTRITIONNUTRITION

NutrientsNutrients

are constituents of food that are constituents of food that provide provide energyenergy & & essential moleculesessential molecules

necessary to sustain normal body functions necessary to sustain normal body functions

1- MacronutrientsMacronutrients (carbohydrates, fats & proteins)

• Provide energyProvide energy• Provide essential molecules Provide essential molecules (essential amino acids & essential fatty acids)(essential amino acids & essential fatty acids)

2 -MicronutrientsMicronutrients

• provide essential moleculesprovide essential molecules ((vitamins & mineralsvitamins & minerals))

As a As a physicianphysician !! !!Why should I study Why should I study

nutritionnutrition???? A physician needs to know kinds & amounts of A physician needs to know kinds & amounts of

macronutrients & micronutrients macronutrients & micronutrients

required to required to

Maintain optimal healthMaintain optimal health

&&

Prevent chronic diseasesPrevent chronic diseases

Definition of the DRIsThe The DRIsDRIs consist of four dietary reference standards for consist of four dietary reference standards for

the intake of nutrients designed for specific age-the intake of nutrients designed for specific age-groups, physiologic state, and sexes.groups, physiologic state, and sexes.

Dietary Reference Intakes (DRIs)

They are estimates of the amounts of nutrients required They are estimates of the amounts of nutrients required to prevent deficiencies & maintain optimal healthto prevent deficiencies & maintain optimal health..

DRIs replace and expand on Recommended DietaryAllowances (RDAs), published in 1941 (with periodic revisions).

DRIs establish upper limits on the consumption of some nutrients and incorporate the role of nutrients in lifelong health, going

beyond deficiency diseases.

BothBoth DRIsDRIs andand RDAsRDAs refer to long-term average daily refer to long-term average daily nutrient intake, because it is not necessary to consume nutrient intake, because it is not necessary to consume

the full RDA every daythe full RDA every day

1- Estimated Average Requirement (EAR)Estimated Average Requirement (EAR)

EAREAR is the average daily nutrient intake level estimated is the average daily nutrient intake level estimated to to

meet the nutrient requirements of meet the nutrient requirements of one half the healthy one half the healthy

individualsindividuals in a particular life stage and gender group in a particular life stage and gender group

It is useful in estimating the actual requirements in groups & It is useful in estimating the actual requirements in groups &

individualsindividuals

2-Recommended Dietary AllowancesRecommended Dietary Allowances(RDA)(RDA)

is the average daily dietary intake level that is sufficient is the average daily dietary intake level that is sufficient to meet the nutrient requirements of to meet the nutrient requirements of nearly all individualsnearly all individuals (97 – 98 %) (97 – 98 %) in a life stage and gender group.in a life stage and gender group.

RDA is notnot the minimal requirement for healthy individuals, BUTBUT it is set to provide a margin of safety for most individualsmargin of safety for most individuals.

EAREAR serves as the base for settingserves as the base for setting RDARDA

• If SD of the of EAR is available and the requirement for the nutrient is normally distributed, the RDA is set at two SDs

above the EAR.

RDARDA = = EAREAR + 2 SD + 2 SD EAREAR

3- Adequate Intake (AI)Adequate Intake (AI)

AI AI is set instead ofis set instead of RDARDA if sufficient scientific evidence if sufficient scientific evidence is is notnot available to calculate an available to calculate an EAREAR oror RDARDA..

&&based on estimates of nutrient intake by a group of based on estimates of nutrient intake by a group of apparently healthy people that are assumed to be apparently healthy people that are assumed to be

adequate.adequate.

For exampleFor example, , Adequate Intake (AI) Adequate Intake (AI) for young infants (whom human milk

is the recommended sole source of food for the first 4-6 months), is based on the estimated daily mean nutrient

intake supplied by human milk for healthy full term infants who are exclusively breast-fed.

4- Tolerable Upper intake Level (UL)Tolerable Upper intake Level (UL)

UL is the highest average daily nutrient intake level that is the highest average daily nutrient intake level that is likely to pose is likely to pose no riskno risk of adverse health effects to of adverse health effects to

almost all individuals in the general populationalmost all individuals in the general population

UL is notnot used as recommended levels of intake.

ULs are useful because of the increased use of dietarysupplements and fortified foods.

ULs apply to chronic daily usechronic daily use.

For some nutrients, there may be insufficient data on which to develop a UL.

Using the DRIsUsing the DRIs

1 -Most nutrients have a set of DRIs.

2 -Usually a nutrient has an EAR and a corresponding RDA , most are set by age and gender, and may be influenced by

special factors such as pregnancy and lactation in women .

3 -When the data are not sufficient to estimate an EAR (or RDA) , then an AI is designated .

The AI is judged by expertsjudged by experts to meet the needs of all individuals in

a group, but is based on less dataless data than in establishing an EAR and RDA

Conclusions

• Intakes below EARbelow EAR need to be improved because the probability of adequacy is 50% or less.

• Intakes between EAR and RDAbetween EAR and RDA probably need to be improved because the probability of adequacy is less than 98%

• Intakes at or above RDAat or above RDA can be considered adequateadequate.

• Intake above AIabove AI can be considered adequateadequate.

• Intakes between UL and RDAbetween UL and RDA can be considered at no riskno risk for adverse effects.

DIETARY MACRONUTRIENTSDIETARY MACRONUTRIENTSEnergy RequirementEnergy Requirement

Energy Requirements in HumansEnergy Requirements in Humans

The estimated energy requirement is the average dietary The estimated energy requirement is the average dietary energy intake predicted to maintain an energy balance in a energy intake predicted to maintain an energy balance in a

healthy adulthealthy adult..

Energy balance occurs when calories consumed are equal toEnergy balance occurs when calories consumed are equal to the energy expendedthe energy expended..

Some simple approximations can provide useful estimatesSome simple approximations can provide useful estimates

sedentary adults require ~ 30 Kcal/kg/dayrequire ~ 30 Kcal/kg/day.. very active adults require ~ 40 kcal/kg/dayrequire ~ 40 kcal/kg/day

Energy Content of FoodEnergy Content of Food

It is calculated from the heat released by the total combustion It is calculated from the heat released by the total combustion of food in a calorimeterof food in a calorimeter..

It is expressed in kilocalories (kcal, or Cal)It is expressed in kilocalories (kcal, or Cal)

The standard conversion factors for determining the metabolic caloric value of fat, carbohydrates and proteins are 9, 4 and 4 Kcal/g respectively.

How Energy is Used in the BodyHow Energy is Used in the Body? ?

1- Resting Metabolic Rate (RMR)Resting Metabolic Rate (RMR)

It is the energy expended by an individual in a It is the energy expended by an individual in a restingresting (basal), (basal), post-absorptivepost-absorptive metabolic state metabolic state

It represents the energy required to carry out the normal body functions as respiration, blood flow, ion transport and

maintenance of cellular integrity

In adults, In adults, RMRRMR is about ~ is about ~ 18001800 Kcal for Kcal for menmen (~ 70 kg) (~ 70 kg) ~ & ~ & 13001300 Kcal for Kcal for womenwomen (~ 50 kg) (~ 50 kg)

5050 – – 7070% % of the daily energy expenditure inof the daily energy expenditure in sedentary individualssedentary individuals is due to is due to RMRRMR

2- Thermic Effect of FoodThermic Effect of Food )diet induced thermogenesis(

It means, the production of heat by the body increases It means, the production of heat by the body increases as much as 30% above the resting levelas much as 30% above the resting level during the digestion and absorption of foodduring the digestion and absorption of food

This is called the thermic effect of food

or diet-induced thermogenesis

Over 24 hour-periods, the thermic response to food Over 24 hour-periods, the thermic response to food intake may amount to about 5– 10 % of the total intake may amount to about 5– 10 % of the total

energy usedenergy used

3-3- Physical Activity Physical Activity

Muscular activity provides the Muscular activity provides the greatest variationgreatest variation in energy in energy expenditure expenditure

The amount of energy consumed depends on the duration The amount of energy consumed depends on the duration and intensity of the exerciseand intensity of the exercise

In general, In general,

sedentary personsedentary person

requires ~ 30–50 % more than RMRrequires ~ 30–50 % more than RMR

highly active individualhighly active individual

may require 100% or more calories above RMRmay require 100% or more calories above RMR

Acceptable Macronutrient Distribution Ranges (AMDRs)

AMDRs are defined as a range of intakes for a particular

macronutrient that is associated with:

• reduced risk of chronic disease • providing adequate amounts of essential nutrients

AMDRsAMDRs for adultsfor adults

4545 – – 6565% % of their total calories from carbohydratescarbohydrates 2020 – – 3535% % of their total calories from fatfat

1010 - -3535% % of their total calories from proteinsproteins

AMDRAMDR represents a balance represents a balance to avoid risks associated with excess consumptionto avoid risks associated with excess consumption

of any particular macronutrientof any particular macronutrient • Very high FAT diets (esp. sat. fas) is associated with: 1- weight gain1- weight gain 2- LDL cholesterol2- LDL cholesterol concentrationconcentration 3-3- increases the risk of coronary heart disease (CHD)increases the risk of coronary heart disease (CHD) • Very high CARBOHYDRATE diets are associated with: 1-1- reduction of HDL cholesterolreduction of HDL cholesterol 2- increase in triglycerides2- increase in triglycerides concentrationsconcentrations 3- increase risk of coronary heart disease (CHD)3- increase risk of coronary heart disease (CHD) • PROTEIN intakes according to AMDR ensures an adequate supply of amino acids for tissue growth,an adequate supply of amino acids for tissue growth, maintenance and repairmaintenance and repair

DIETARY MACRONUTRIENTSDIETARY MACRONUTRIENTSBIOLOGIC PROPERTIESBIOLOGIC PROPERTIES

The incidence of a number of chronic The incidence of a number of chronic diseases are significantly influenced diseases are significantly influenced

by the by the kindskinds and and amountsamounts of nutrients of nutrients consumed consumed

For example,For example,The role of the dietary fats and the risk of coronary The role of the dietary fats and the risk of coronary

heart diseases (CHD)heart diseases (CHD)

Diet Diet

CarbohydratesCarbohydrates

Diet CarbohydratesDiet CarbohydratesClassificationClassification

A- Simple Sugars: A- Simple Sugars: Monosaccharides

Disaccharides

B- Complex carbohydrates: B- Complex carbohydrates: Polysaccharides

C- FiberC- Fiber

A- A- Simple Sugars:Simple Sugars:

1- 1- MonosaccharidesMonosaccharides:: Glucose & fructose: the principal monosaccharides in food Free glucose & fructose: available in fruits & bee honey

2-2- DisaccharidesDisaccharides:: Sucrose (glucose + fructose: in table sugar & molasses Lactose (glucose + galactose: in milkMaltose (glucose + glucose) : in malt liquors

B- B- Complex Carbohydrates Complex Carbohydrates (Polysaccharides)(Polysaccharides)Starch: are polymers of glucose & do not have a sweet taste.is a complex carbohydrate that is found in abundance in plants:wheat & other grains, potatos, peas, beans & vegetables

Diet Carbohydrates Diet Carbohydrates cont.

ClassificationClassification

C- C- Fiber:Fiber:

1-1-Dietary fiberDietary fiber: the nondigestible carbohydrates & is present in plants. provides little energy but has several beneficial effects 2-2-Functional fiberFunctional fiber: : the isolated, extracted or synthetic fiber that has proven health benefits. 3-3-Total fiberTotal fiber: : the sum of dietary fiber & functional fiber. 4-4-Soluble fiberSoluble fiber:: refers to fibers that form a viscous gel when mixed with a liquid. 5-5-Insoluble fiberInsoluble fiber:: passes through the digestive tract largely intact.



Functions of dietary fiber:Functions of dietary fiber: 1- 1- Reduces constipation & hemorrhoids formationReduces constipation & hemorrhoids formation Fiber adds to the bulk of diet as it can adsorb 10- 15 times its own weight

water drawing fluid into the lumen of the intestine and increase bowl motility

2- 2- Delays gastric emptyingDelays gastric emptying which can result in: i- sensation of fullness ii-reduced peak of blood glucose following a meal.

3- 3- Lower plasma LDL cholesterol (with reducing risk of CHD)Lower plasma LDL cholesterol (with reducing risk of CHD) By decreasing absorption of cholesterol & other fats So, it increases fecal loss of cholesterol & interfering with bile acid reabsorption



Recommended daily intake of fiberRecommended daily intake of fiber (AI) (AI)

25 grams for women25 grams for women38 grams for men38 grams for men(~ 40 grams /day)(~ 40 grams /day)

Amount of fiber in our diet has to be Increased than currently consumed (for example: American diets contains only ~ 11 grams/day)



• Some carbohydrate-containing foods produce a rapid rise followed by a steep fall in blood glucose concentration,

• whereaswhereas others result in gradual rise followed by a slow decline.

The Glycemic IndexThe Glycemic Index

is defined as the area under the blood glucose curves seen after ingestion of meal with carbohydrate-rich food, compared with the area under the blood glucose curve after a meal consisting of the

same amount of carbohydrates in the form of glucose or white bread.

Food with low glycemic indexFood with low glycemic index

tends to • create sense of satiety over a longer period of time

• & may help to limit caloric intake

Diet Carbohydrates Diet Carbohydrates & Blood Glucose& Blood Glucose

Carbohydrates are not essentialnot essential nutrients, because the carbon skeletons of amino acids can be converted into glucose.

HOWEVER

the absence of dietary carbohydrate leads to the absence of dietary carbohydrate leads to degradation of body proteins whose degradation of body proteins whose

constituent amino acids provide the carbon skeleton for constituent amino acids provide the carbon skeleton for gluconeogenesis.gluconeogenesis.

Diet Carbohydrates Diet Carbohydrates RequirementsRequirements

• Is set at 130 g/day130 g/day for adults & children for adults & children based on the amount of glucose used by carbohydrate dependent tissues (as brain & RBCs).

• However, this level of intake is usually exceeded to meet energy needs.

• Adults should consume 45 – 65 % of their total calories45 – 65 % of their total calories from carbohydrates.

• Added sugarAdded sugar shouldshould not represent more than 25%not represent more than 25% of of total energytotal energy as sugar may displace nutrient-rich foods from the diet, potentially leading to deficiencies of certain micronutrients (as vitamins & minerals)

Diet Carbohydrates Diet Carbohydrates RDARDA

• Carbohydrates result in Carbohydrates result in fat synthesis fat synthesis onlyonly when when consumed in excess of body needs of energy.consumed in excess of body needs of energy.

• Excess sucrose ingestion may increase risk of Excess sucrose ingestion may increase risk of dental dental cariescaries..

Diet Carbohydrates Diet Carbohydrates Simple Sugars & DiseasesSimple Sugars & Diseases

Diet Diet

ProteinProtein

• the protein in food provides essential amino acid.

• 10 of the 20 amino acids needed for the synthesis of body proteins are essential. i.e. can not be synthesized in humans at an adequate rate

• 8 of these 10 are essential at all times.

• Argenine and histidine are required during periods of rapid tissue growth as in childhood and recovery from illness.

Diet ProteinsDiet Proteins

The quality of diet protein The quality of diet protein

is a measure of its ability to provide the essential is a measure of its ability to provide the essential amino acids required for tissue maintenanceamino acids required for tissue maintenance

The protein quality is evaluated by the following standardThe protein quality is evaluated by the following standard::

PProtein rotein DDigestibility igestibility CCorrected orrected AAmino mino AAcid cid SScoring coring

((PDCAASPDCAAS))• which is based on 1) the profile of essential amino acidsessential amino acids 2) the digestibilitydigestibility of the protein• The highest possible score is The highest possible score is 1.001.00

Diet Proteins Diet Proteins cont.

QualityQuality

1- 1- Animal Sources ProteinsAnimal Sources Proteins

with a high qualityhigh quality as they contain all essential amino acids in proportions similar to those required for synthesis of human tissue proteins.

(except for gelatin except for gelatin prepared from animal collagen which is of low biological value as a result of deficiencies in several essential amino acids).

2- 2- Plant Sources ProteinsPlant Sources Proteins

• Proteins from wheat, corn, rice & beanswheat, corn, rice & beans• with a a lower qualitylower quality than of animal proteins.• Proteins from different plant sources may be combined in a way that the

result is equivalent in nutritional value to animal proteins..


SourcesSources

Nitrogen balance occurs when the amount of nitrogen Nitrogen balance occurs when the amount of nitrogen consumedconsumed equals equals that of the nitrogen that of the nitrogen excretedexcreted in urine, sweat and faeces. in urine, sweat and faeces.

1- 1- Positive nitrogen balancePositive nitrogen balance

nitrogen intake exceeds nitrogen excretion (loss). occurs in situations in which tissue growth occurs as in children, pregnancy or during recovery from an emaciating illness. 2- 2- Negative nitrogen balanceNegative nitrogen balance

nitrogen loss is exceeds nitrogen intake. occurs with inadequate dietary protein, lack of essential amino acids, or during

physiologic stresses as trauma, burns, illness or surgery.


Nitrogen BalanceNitrogen Balance

• The greater the proportion of animal protein included in diet, the less the protein is required.

• RDARDA for protein is computed for proteins of mixed biological value at 0.8 g/kg/day 0.8 g/kg/day for adults

• People who exercise on a regular basis People who exercise on a regular basis may benefit from the extra protein to maintain muscle mass. 1g/kg/day1g/kg/day is recommended for athletes

• PregnantPregnant & & lactatinglactating women require up to 30 g/day in addition to their basal requirements.

• ChildrenChildren should consume 2 g/kg/day 2 g/kg/day to support growth.


RequirementsRequirements

• There are no physiologic advantagesno physiologic advantages to the consumption of more protein than the RDA.

• Proteins consumed in excess of the body's needs is deaminated and the resulting carbon skeleton metabolized to provide:

1- energy or 2- acetyl CoA for fatty acid synthesis


Consumption of excess proteinsConsumption of excess proteins

When the intake of the carbohydrates is low, amino acids are deaminated to provide carbon skeleton for the synthesis of glucose that is needed for energy production especially to Brain (gluconeogenesis).

If carbohydrates intake is If carbohydrates intake is less than 130 g/dayless than 130 g/day, a great amount of proteins are metabolized to provide precursors of gluconeogenesis (protein loss)

Therefore, carbohydrate is considered to be carbohydrate is considered to be protein-sparingprotein-sparing, as it allows amino acids to be used for repair and maintenance of tissue protein instead of being used for gluconeogenesis.


Protein sparing effect of carbohydratesProtein sparing effect of carbohydrates

1-1-Related to a nutritional statusRelated to a nutritional status: inadequate intake of protein (common in poor countries) and/or energy

2-2-Related to a medical conditionRelated to a medical condition: : Chronic illness (common in developed countries) Major trauma Severe infection Major surgery

Affected individuals show a variety of symptoms, including: Affected individuals show a variety of symptoms, including: depressed immune system with a reduced ability to resist infection. Death due to a secondary infection is common.

Two extreme forms of malnutrition are observed:Two extreme forms of malnutrition are observed:• KWASHIORKORKWASHIORKOR• MARASMUSMARASMUS


Protein-Calorie MalnutritionProtein-Calorie Malnutrition

1- KWASHIORKORKWASHIORKOR

• Kwashirkor occurs when proteinprotein deprivation is relatively greater than the reduction in total caloriescalories. • Frequent in children after weaning at about one year of agechildren after weaning at about one year of age,

when their diet consists predominantly of carbohydrates.

• Typical symptoms include: Decreased blood albumin concentration Decreased blood albumin concentration Edema Edema Stunted growthStunted growth Skin lesionsSkin lesions Depigmentated hairDepigmentated hair AnorexiaAnorexia Enlarged fatty liver Enlarged fatty liver



2- MARASMUS • Marasmus occurs when caloriecalorie deprivation is relatively greater than

the reduction of protein.

• Marasmus usually occurs in children younger than one year of children younger than one year of age age when the mother's breast milk is supplemented with native cereals which are usually deficient in protein and calories.

• Typical symptoms include:Typical symptoms include: arrested growtharrested growth extreme muscular wastingextreme muscular wasting weakness and weakness and anemia. anemia. No edemaNo edema or changes in plasma proteins (albumin). or changes in plasma proteins (albumin).



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