Scientific Facts About Foods & Nutrition

Nutrition is the science of food and its relationship to health. The subject of food & nutrition is very extensive. Through centuries, food has been recognized as important for human beings in health and disease. The history of man has been to large extent struggle to obtain food. Great advances have been made during last 50 years in knowledge of nutrition and in the practical application of that knowledge. Specific nutritional diseases have been identified and technologies developed to control them, for example protein energy malnutrition, endemic goiter, nutritional anemia, and nutritional blindness.
Foods/nutrients can be classified into five major categories 1) Proteins 2) Fats 3) Carbohydrates 4) Vitamins 5) minerals.


Proteins are the building blocks of human body. The word protein means, Of first importance. Indeed they are of the greatest importance in human nutrition. Proteins are complex nitrogenous compounds. They contain carbon, hydrogen, oxygen, nitrogen, and sulfur in varying amount. Proteins differ from carbohydrates and fats in that they contain nitrogen; this is usually 16 % of protein. Proteins constitute about 20% of body weight.
Proteins are made up of smaller units, called amino acids. Some 24 amino acids are required by human body, of which 9 are called “essential” because the body can not synthesize them in amounts what is needed by the body, and therefore they must be obtained from dietary sources. They are: leucine, isoleucine, lysine, metheonine, phenylalanine, threonine, valine, tryptophan, and histidine. Non essential amino acids (which are synthesized in the body) include asparagenic acids, serine, glutamic acid, praline and glycine, arginine. Both essential and non essential amino acids are required for synthesis of proteins. New tissues can not be formed unless all essential amino acids (EAA) are present in the diet. A protein is said to be biologically complete if it contain all the EAAs. if it is lacking in one or more EAAs it is biologically incomplete. From nutritional point of view animal proteins are rated superior to vegetable proteins. Milk and egg proteins are most suitable for humans. If one is a pure vegetarian than he should combine two or more vegetable proteins to overcome deficiencies of EAAs.
Functions of proteins: proteins give 4 kcal of energy per gram. Proteins are required for body building, repair and maintenance of body tissues, synthesis of substances like, antibodies, plasma proteins, hemoglobin, enzymes, and coagulation factors. Proteins are required for immune mechanism of body.
Sources of proteins: Animal sources include, milk, meat, egg, fish, cheese etc. Vegetable sources include pulses, cereals, nuts, oil-seed cakes etc.
Protein requirement is expressed in terms of body weight. Protein requirement of humans is 1 gram/kg/day.


Fats are solid at 20 C, they are called oils if they are liquid at that temperature. They can be classified into simple lipids, compound lipids, and derived lipids. Most of the body fat (99%) in adipose tissue is in the form of simple lipid. Adipose tissue constitute 10-15 % of body weight, if it is more than that it is obesity. Fatty acids can be divided into saturated and unsaturated. Some of the fatty acids can not be synthesized in the body, they have to be obtained from dietary sources and are called essential fatty acids (EFA). Saturated fatty acids increase amount of cholesterol and unsaturated fatty acids reduce cholesterol.

Sources of fat:
1) Animal fats- major sources are butter, milk, cheese, eggs, fats of meat and fish. Animal fats except cod liver oil and fish oils are mostly saturated fats and increase cholesterol. Thats why animal fats should be consumed less.
2) Vegetable fats- plants store fat in there seeds, e.g. ground nut, mustard, coconut, sesame, sunflower. They contain large amount of unsaturated fat and reduce cholesterol. There percentage should be higher in food compare to animal fat.
3) Other sources- small quantities of fat (invisible fat) are found in most foods like, cereals, pulses, vegetables.
Fats are high energy foods; they provide 9 kcal of energy per gram. WHO expert committee on Prevention of Coronary Heart Diseases has recommended only 20-30% of total dietary intake of calories. At least 50% should be vegetable fat. But in developed countries it is more than 30-40%.


The third major component of food is carbohydrate, which is the main source of energy, providing 4 kcal of energy per gram. They are essential for synthesis of certain non essential amino acids. Carbohydrate reserve of human body is about 500 grams.
There are three main sources of carbohydrates viz. starches, sugars and cellulose. Starch is basic to human diet. It is found in abundance in cereals, roots and tubers. Sugars comprise monosaccharide (glucose, fructose galactose) and disaccharides (sucrose, lactose). Cellulose is the indigestible part of carbohydrate which do not contribute calorie. They contribute to dietary fiber. Dietary fibers are mainly non starch polysaccharides physiologically important. They are found in fruits, vegetables, and grains. Fiber has many functions. It absorbs water and this increase the bulk of the stool, which prevents constipation, by encouraging bowel movement.
Dietary fiber should be more than 40 grams per day. A well balanced diet provides that much of roughage. Excess fiber also decreases absorption of micronutrients. Fiber may also bind to vitamins and minerals like, zinc, iron, and reduce their bioavailability.


Vitamins are divided into two groups (a) fat soluble vitamins viz. vitamins A, D, E, and K and (b) water soluble vitamins viz. vitamins B- Complex group and C. each vitamins has specific function to perform and deficiency of any particular vitamin may lead to specific deficiency disease. Minimum requirement of the vitamins has been determined.
Vitamin A:

daily requirement is 600 micrograms (mcg) for adults, 350 mcg for infants, and 950 mcg for lactating mothers, and children of 1-6 years need 400 mcg.
Sources of vitamin A include liver, egg, meat fish, milk, green leafy vegetables (darker the leaf, more the vitamin content), yellow fruits and vegetables like papaya, mango, pumpkin, tomato etc. Human body can store vitamin in body mainly in liver, which is sufficient for 6-9 months. Deficiency of vitamin A can cause many symptoms like, night blindness, conjunctival xerosis, Bitot’s spot, corneal xerosis, keratomalacia.
Vitamin D:

Daily requirement of vitamin D are 2.5 mcg for adults, 5 mcg for infant and children, and 10 mcg in pregnancy and lactation.
Vitamin D is unique because it is derived from sunlight; it is synthesized by the body by the action of UV (ultra violet) rays of sunlight, which is stored in the skin.Sources of vitamin D are only animal origin. Liver, egg yolk butter, cheese is rich in vitamin D.
Deficiency of vitamin D causes Rickets and osteomalacia.
Vitamin E:

Vitamin E does not have serious deficiency syndrome. Sources of vitamin E are vegetable oil, sunflower seeds, egg, butter etc. vitamin E is very important in maintaining skin texture.
Vitamin K:

It occurs in two forms vit K1 and vit K2. Sources include fresh dark green leafy vegetables, cow’s milk, and liver. Vitamin K2 is synthesized by the intestinal bacteria, which usually provide adequate supply of vitamin in man. It stimulates certain coagulation factors and deficiency of vitamin K can cause bleeding disorders. The daily requirement of vitamin K is 0.03 mg.
B-complex group of vitamin include thiamin (B1), riboflavin(B2), niacin, pyridoxine(B6), pantothenic acid, folic acid, vitamin B12.
Thiamin is water soluble vitamin. Its daily requirement is 0.5 mg per 1000 kcal energy intake. Important sources are whole grain cereals, wheat, gram, yeast, pulses, groundnut, meat, fish, egg, vegetables. Being water soluble thiamin is readily lost on boiling and washing. It is also lost on prolonged storage. Deficiency of thiamin causes beriberi and Wernick’s encephalopathy. Beriberi is three types dry beriberi, wet beriberi, and infantile beriberi. Because of improved socio-economic status throughout the world beriberi is very rare nowadays.
Daily requirement of riboflavin is 0.6 mg per 1000 kcal of energy intake. Its sources are milk, egg yolk, liver, kidney, and green leafy vegetables. Germination increase riboflavin content of cereals. Deficiency causes angular stomatitis (ulceration and infection of angle of mouth), glossitis.
Niacin is essential for metabolism of carbohydrate, fat and protein. It is also essential for normal functioning of skin, intestine and nervous system. Daily requirement is 6.6 mg per 1000 kcal energy intake. Sources include liver, kidney, poultry, fish, legumes, and groundnut. Deficiency of niacin causes Pellagra. Symptoms of pellagra include diarrhea, dermatitis, dementia (forgetfulness). This condition is rare these days.
Pyridoxine deficiency is rare because our daily diet generally contain enough of it. Its daily requirement is 2 mg/day for adults and 2.5 mg/day for pregnancy and lactation. Sources include egg, milk, liver, meat, grain cereals, legumes, vegetables.

Sources of folic acid include green leafy vegetables, meat, liver, dairy products, egg, milk, fruits and cereals. Daily requirement is 100 mcg (micrograms) for adults, 400 mcg for pregnancy, and 150 mcg for lactation. Severe deficiency during pregnancy can cause congenital malformation. It can also cause infertility or even sterility. Body store of folic acid is small 5-10 mg, so folic acid deficiency develops very fast.
Vitamin B12 is available only in animal sources. So, pure vegetarians can develop B12 deficiency. B12 is required for formation of hemoglobin. B12 cooperate with folic acid in the synthesis of DNA. Sources include egg, milk, fish, meat, and kidney. It is also synthesized by bacteria in colon.Daily requirement is 1 mcg/day for adults and 1.5 mcg for pregnancy and lactation.
Vitamin C: vitamin C (ascorbic acid) is water soluble. It is the most heat sensitive of all vitamins. Vitamin C is antioxidant, and play important role in tissue oxidation. It is needed for formation of collagen, which provide supporting matrix to blood vessels, connective tissues, bones and cartilage. That’s why in vitamin C deficiency bones fracture easily and bleeding occurs, as seen in scurvy, a vitamin C deficiency disease. Main dietary sources are fresh fruits and green vegetables. Liver is rich source. Indian gooseberry is the richest source of vitamin C. daily requirement is about 60 mg/day.


Minerals which are required by the body are calcium, sodium, potassium, phosphorus, magnesium. Trace elements like zinc, copper, cobalt, chromium, selenium, molybdenum, nickel, tin, silicon, vanadium, manganese, iron, fluorine, are also required.
Calcium is required for the maintenance and development of bones. Daily requirement is about half gram. Deficiency may cause softening of bones. Sources include milk and milk products, cheese, egg, fish, meat. Cereals and vegetables also contain good amount of calcium.

Iron is very important trace element. The main function of iron is oxygen transport and cell respiration. Daily requirement of iron is 30 mgs. Women require more iron due to loss of iron in menstruation. Other minerals and trace elements are also very important in daily functioning of body.
It is required for synthesis of hemoglobin. Iron deficiency causes anemia. Iron is also required for brain development and its function, regulation of body temperature.


“Image courtesy of Stuart Miles /”.

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