INTRODUCTION

What is “Food” and what is “Nutrition”?

Food is any edible material that supports growth, repair and maintenance of the body. Food also protects the body from infections and diseases.

Nutrition is the process by which body utilizes food for growth and maintenance and healthy living.

Food functions in the body through the nutrients

it contains

What are nutrients?

Nutrients are substances found in food. These are:

•Carbohydrate

•Fat/Oil

•Protein

•Vitamins

•Minerals

  Since Water is indispensable for life, it is considered both as a food and as a nutrient.

  Dietary Fibre and some Phytochemicals of plant foods, although not nutrients as such, are needed for good

health.

• What food does in the body does through the nutrients it contains. The body utilizes these nutrients to grow and keep healthy and strong. All nutrients needed by the body are available through food.

• No food by itself (except for breastmilk which is adequate for babies up to six months of age) has all the nutrients needed for full growth and health. Food therefore must be balanced.

• We therefore need a variety of foods to get all the nutrients the body needs.

Each nutrient has its own function in the body.

Specific nutrients do their best work in the body when present with other nutrients.

Nutrients are therefore mutually supportive.

What are Macronutrients and Micronutrients?

The nutrients can be divided into two major groups – “Macronutrients” and “Micronutrients”.

 

Macronutrients are those that are needed in large quantities (tens or hundreds of grams) every day. These are: Carbohydrates, protein and fats/oils.

 

Micronutrients are those that are needed in minute quantities (micrograms or at best milligrams). These are vitamins, minerals and trace elements.

Carbohydrates

Main function is energy production in the body. 

Largest source of energy: 40 - 80 percent of the total energy intake in different countries. Neither extreme is good. The ideal contribution is 60 percent. 

One gram of carbohydrate provides 4 Kcal. 

Grains (rice, wheat, maize), roots and tubers (potato, sweet potato, guam, banana) and legumes (pulses, nuts) are rich sources of carbohydrates.

Sweet fruits and some vegetables also provide carbohydrate in the form of sugar.

 

Milk sugar is lactose.

 

Honey has high content of fructose, the sweetest of all sugars.

 

Soft drinks contain sugar but almost no other nutrients.

Carbohydrates are present in two forms:

 

Simple carbohydrates: glucose, fructose, sugar

Compound carbohydrates: starch in plants and glycogen in animals (liver and muscles)

Compound carbohydrates are polymers of glucose.

Carbohydrates and sugars

Digestion in the intestine

Glucose (plus other monosaccharides)

Absorbed into blood

In presence of insulin

Taken up by cells

In presence of O2

Metabolized to CO2 + H2O + Energy

(no side effects in glucose use in the body)

During well-fed conditions, body glucose is stored in liver and muscles as glycogen, a compound carbohydrate. Glycogen is therefore the animal counterpart of plant starch. 

During starvation, glycogen of liver and muscle is broken into glucose to provide energy.  

Glucose is the only metabolic fuel for the brain under normal conditions. 

Carbohydrates taken in excess of energy requirements are directly converted into fat and deposited in the body.

Protein

 Protein is the building material for all body parts, such as muscle, brain, blood, skin, hair, nails, bones and body fluids.

It is essential for growth, repair of worn-out tissues, replacement of used-up blood and resistance against infections. 

Protein comes from both animal and plant foods.

Meat, fish, egg, and milk and milk products are rich sources of animal protein. 

Pulses, nuts and beans are rich sources of plant protein.

 Cereals are low in protein (e.g. rice: 6 – 8%, wheat: 12 – 14%), but because of their large quantities in the diet, they meet a major portion of total dietary protein requirement.

Animal proteins are of high quality (“first-class” proteins) because of their more complete and balanced composition of amino acids. 

Plant proteins are of lower quality (“second-class” proteins) because they are incomplete in one or more of the essential amino acids. 

Combination of two or more plant foods can mutually supplement each other’s deficiency and therefore give rise to high quality protein. For example, khichuri, which is a mixture of rice and dal (pulse), is a good quality diet.

The protein from beans and legumes are of better quality than the protein from rice and wheat products. These foods are considered less expensive meat substitutes and are often called the ‘poor man’s meat’.

 

Potato is poor in protein (<3%), but this protein is of high quality.

Proteins are polymers of smaller units called amino acids, some of which can be manufactured in the body (so-called “non-essential”), and others must be provided pre-formed by food (the essential amino acids).

Protein

Digestion in the

gastro-intestinal tract

Amino acids

Absorbed into blood

Taken up by the cells

Synthesize body proteins

Although the main function of protein is to build and maintain the body, it also gives energy.

One gram of protein gives 4 Kcal.

Fats/Oils

Fats/oils are concentrated sources of energy needed by the body.

The term “fat” is commonly used to refer to a family of compounds called “lipids” which are water-insoluble.

They include triglycerides, phospholipids and sterols such as cholesterol. Triglycerides predominate both in the food and in the body.

1 gm of fat provides 9 kcal, i.e. more than double the energy given by carbohydrate or protein per unit weight.

Chemically, triglycerides are fatty acid tri-esters of glycerol:

 

H2C – O – CO – fatty acid 

HC – O – CO – fatty acid 

H2C – O – CO – fatty acid

Fats

A triglyceride may be a FAT or OIL, depending on the predominant type of fatty acids it contains: saturated, monounsaturated and polyunsaturated.

When predominant fatty acids are saturated and monounsaturated, then it is solid at room temperature and is termed as FAT.

Usually, triglycerides of land animal sources are FATs.

Examples are fats of beef, mutton, goat and chicken skin.

Saturated fatty acids are cholesterologenic, i.e. they increase blood cholesterol level.

Aquatic animals like the fish, especially the marine fish, have good preponderance of polyunsaturated fatty acids and their fat is actually OIL.

Oils

When polyunsaturated fatty acids predominate, then it is liquid at room temperature and is termed as OIL.

Usually, triglycerides of plant sources are OILs.

Examples are vegetable oils - mustard oil, soybean oil, sunflower oil, corn oil and other cooking oils.

However, coconut and palm oil contain large proportions of saturated and monounsaturated fatty acids.

Cholesterol

Some food items are rich in preformed cholesterol. Examples: egg yolk, liver, brain, chicken skin.

Forms of blood cholesterol

HDL = Good cholesterol

LDL = Bad cholesterol

Fat provides the building materials for some body parts, such as brain, nerves and hormones.

It also facilitates absorption, transport and storage of fat-soluble vitamins A, D, E and K.

Fat is therefore an essential nutrient. Like all other nutrients, fat is beneficial if consumed in the right amount and if it is the right type.

Since high blood cholesterol is a risk factor for coronary heart disease, diet rich in preformed cholesterol and saturated fat is to taken with caution after a certain age. It is, however, not a problem for infants and young growing children.

Vitamins

• Vitamins are food constituents vital for life. They cannot be synthesized in the body and must therefore be taken with food. They are, however, needed in minute amounts.

• Vitamins help in the metabolism and utilization of the carbohydrate, protein and fat in the cells. They act as helpers (coenzymes) of enzymes involved in these metabolisms.

• Vitamins thus help regulate body functions and maintain health. They also protect the body against infections.

Vitamins are either water-soluble or fat-soluble.

• Water-soluble vitamins are the B-complex vitamins and vitamin C.

• B-complex vitamins are vitamin B1, B2, B6, B12,

niacin, folic acid, biotin, pantothenic acid.

• Fat soluble vitamins are vitamins A, D, E and K.

• Soluble vitamins, when taken in excess of body needs, are excreted in urine.

• On the other hand, fat-soluble vitamins, when taken in excess, are stored in the body (particularly liver) for use at times when the intake of these vitamins is inadequate.

• Most vitamins can be derived from liver, fruits, vegetables, legumes and grains.

A few of the key roles and rich dietary sources of some vitamins of public health importance are listed in the table below.

Function Rich sources

Thiamin(vitamin B1)

Helps release energy from nutrients; supports normal appetite and nerve function

Cereal grains, pulses, yeasts; Green vegetables, fish, meat, fruit, milk

Riboflavin(vitamin B2)

Helps release energy from nutrients; supports skin health; prevents deficiency manifested by cracks and redness at corners of mouth, inflammation of the tongue and dermatitis

Milk and its non-fat products; Green vegetables, meat, fish, egg

Niacin Helps release energy from nutrients; supports skin, nervous and digestive systems

Liver, ground nuts, cereal bran or germ

Pyridoxine(Vitamin B6)

Helps make red blood cells; helps in amino acid and fatty acid metabolism

Widely present in both plant and animal foods

Folic acid Helps in the formation of DNA and new blood cells including red blood cells; prevents anemia, some birth defects, heart disease

Dark-green leaves, liver, kidney

Vitamin C Helps in the formation of protein, collagen, bone, teeth, cartilage, skin and scar tissue; facilitates the absorption of iron from the gastrointestinal tract; involved in amino acid metabolism; increases resistance to infection

Fruits, vegetables and dark-green leaves

Vitamin A Maintains normal vision, skin health, bone and tooth growth, reproduction and immune function, prevents xerophthalmia

Animal sources: Butter, eggs, milk, liver;Plant sources: Dark-green leafy vegetables, mangoes, papaya, tomato

Helps in the mineralization of bones by enhancing absorption of calcium

Fish liver oils, eggs, cheese, milk and butter; Sunlight induces synthesis of vit. D in the body from skin cholesterol.

Strong antioxidant; helps prevent atherosclerosis; protects neuromuscular system; important for normal immune function

Vegetable oils, germinated whole-grain cereals

Vitamin D

Vitamin E

Minerals

Minerals are inorganic chemical elements present throughout the body in varying amounts. Like the vitamins, they cannot be synthesized in the body and must be taken with food.

Minerals act as co-factors of enzymes for metabolism.

Minerals form part of the structure of body tissues, such as bones, teeth and nails, blood, nerves and muscles.

Minerals are vital to physical and mental development. They also help protect the body against infections.

Meat, fish, milk, cheese, green leafy vegetables and legumes provide most of the minerals needed by the body.

Some of the key roles of minerals are shown in the table below.

Mineral Function

Calcium 

Mineralization of bones and teeth; regulator of many of the body’s biochemical processes; involved in blood clotting, muscle contraction and relaxation, nerve function, blood pressure and immune defenses

Phosphorous Mineralization of bones and teeth; part of every cell; used in energy transfer and maintenance of acid-base balance

Sodium Maintains normal fluid and electrolyte balance, assists nerve impulse initiation and muscle contraction

Chloride Maintains normal fluid and electrolyte balance

Chromium Works with insulin and is required for release of energy from glucose

Copper Necessary for absorption and use of iron in the formation of hemoglobin

Fluoride Involved in the formation of dental enamel and prevents dental caries; involved in the formation of teeth and skeleton and inhibits osteoporosis in old age 

Iodine As part of the two thyroid hormones, iodine regulates growth, physical and mental development and metabolic rate

Iron Essential in the formation of blood; involved in the transport and storage of oxygen in the blood and is a cofactor bound to several non-heme enzymes required for the proper functioning of cells

Sulfur Integral part of vitamins, biotin and thiamin, as well as the hormone insulin

Zinc Essential for normal growth, development, reproduction and immunity

Magnesium Involved in bone formation and tissue energy metabolism

Dietary Fibre

• Dietary fibres are non-digestible, non-absorbable components of food.

• Fibres form the bulk of the stool and help in clearing the bowel and in preventing constipation

and colon cancer.

• Fibres inhibit absorption of glucose and cholesterol from the GI tract, thus are helpful in diabetes and heart disease.

• Fruits, vegetables, pulses and whole cereals are sources of dietary fibre.

• Our daily diet should contain some fibre for good health and well being.

Non-nutrient components of health significance

• Some plant foods show additional health benefits beyond basic nutrition. These foods are called “Functional Foods”.

• These ingredients protect our body from various diseases like diabetes, hypertension, and some forms of cancer.

• Bright examples of functional foods are tomatoes, mushroom, apple and guava, garlic, onion, ginger, cloves and other spices, cabbage, cauliflower, broccoli, blackberry, and tea.

• The above functional foods should be a part of our daily dietary.