Nutrients are classified into five major groups: proteins, carbohydrates, fats, vitamins, and minerals. These groups comprise between 45 and 50 substances that scientists have established, mostly through experiments with animals, as essential for maintaining normal growth and health. Besides water and oxygen, they include about eight amino acids from proteins, four fat-soluble and ten water-soluble vitamins, about ten minerals, and three electrolytes. Although carbohydrates are needed for the body’s energy, they are not considered absolutely essential, because protein can be converted for this purpose.

The body uses energy to carry on vital activities and to maintain itself at a constant temperature. By using a calorimeter, scientists have been able to establish the energy amounts of the body’s fuels—carbohydrates, fats, and protein. About 4 calories each are yielded by 1 g (0.035 oz) of pure carbohydrate and 1 gram of pure protein; 1 gram of pure fat yields about 9 calories[1].

Carbohydrates are the most abundant foods in the world, and fats are the most concentrated and easily stored fuel. If the body exhausts its available carbohydrates and fats, it can use proteins directly from the diet or break down its own protein tissue to make fuel. Alcohol is also a source of energy and yields 7 calories per gram. Alcohol cannot be oxidized by the body cells but must be processed by the liver into fat, which is then stored by the liver or in the adipose tissue.

Carbohydrates

More than 50 per cent of energy content of the common diet comes from carbohydrates. For a normal person about 70 g. of proteins and about 400 to 500 g. of carbohydrates are recommended. The requirements of a growing child, a nursing mother and during certain disease generally increase. A sportsman needs two and a half times more carbohydrates than a resting person.

Potatoes, bread, rice, sweet corn etc. contain high percentage of starch, which is a useful energy yielding substance. Sweet foods contain sugars. In animals and plants several other forms of carbohydrates like glucose, maltose and lactose are found. Glycogen is an insoluble carbohydrate found in the liver and muscles of animals. In the event of deficiency of energy, glycogen is rapidly converted into glucose, which is carried to the different parts of body by the blood. Cellulose is present in all plants since it is the main constituent of cell wall. Very few animals can digest it. Herbivores have special part in their gut where microorganisms act on cellulose and break it down but in most animals it remains unchanged and contributes to the roughage in the diet.

Fats and Oils

It constitutes a major source of energy, about twice that of carbohydrates. It is advisable that the normal diet of 3000 K. Cal should contain at least 75 g of fats. This should always be raised when there is a significant increase in the energy expenditure of the body.

Like carbohydrates, fats contain only carbon, hydrogen, and oxygen but in different proportion. They are compounds of glycerol with fatty acids.

Fats remain solid at 20C but oils are liquid at high temperature. Butter, cooking oils etc. consist almost entirely of fat but milk, cheese, egg, some fishes, nuts and even meat contain considerable amount of fats. Fat can be stored in the body providing useful energy reserves. The layers of fatty tissues lying just below the skin have insulating function.

Protein

 It is the most significant constituent of the diet.

The basic unit of protein in amino acids. Man requires in his diet eight of the twenty amino acids from which he can synthesize the other twelve. Animal foods such as milk meat or egg contain almost all the essential amino acids. When vegetable sources are to be relied upon for proteins. It becomes necessary that a combination of cereals and pulses be consumed in the proportion of 10:1 to meet the body requirement of the essential amino acids. The different amino acids are required:

(1)   To form new tissues during the period of growth or pregnancy.

(2)   To overcome wear and tear.

(3)   To maintain the protoplasmic structure of the cell.

(4)   To provide milk proteins during lactation.

(5)   To furnish the raw materials for the manufacture of external secretions such as digestive enzymes and some protein hormones.

The protein requirements per day of various age groups are: -

• 1. Children between 2-8 years 22-3 g
• 2. Children between 13-17 years 43-53 g.
• 3. Moderately active males and females 45-56 g.
• 4. During pregnancy 65 g.
• 5. During lactation 70 g.

Minerals

A wide variety of salts is essential for the metabolic activities of the body and for the construction of certain tissues, they are needed to build bones, teeth, in blood coagulation, functioning of muscles, nerves, thyroid gland, and formation of RBC and providing resistance against diseases. Except Sodium Chloride (Common Salt) minerals are not taken in as pure salts, they enter as charged ions eg K, Mg2 or in organic compounds like the phosphorus in nucleic acids. Adequate requirements of some important minerals in the diet per day are as follows:

Mineral salts and their importance

Vitamins

 Although these have no energy value, they are important accessory substances, which contribute to the maintenance of health ‘Funk’ for the first time, used the terms vitamin.

Plants can make vitamins from simple substances, but animals mostly obtained them readymade directly on indirectly from plants. Minimum requirements of vitamins in the diet per day, sources of different vitamins and deficiency symptoms are given below:

Water

Water is a universal solvent in the body. It is medium in which all metabolic reactions take place. It is obtained in dietary liquid, solid food, and also by oxidation of organic foodstuffs. Water, besides becoming a part of protoplasm, tissue fluid, is important for transporting substances from one part to another part and eliminating wastes outside the body. It also plays an important role in regulating body temperature and osmotic pressure of the body fluid.

Nutritional Disorders

Protein Caloric Malnutrition (PCM)

a.    Kwashiorkor: When small babies, instead of taking their mother’s milk, take mainly a carbohydrate diet the children become irritable, cease to grow and lose weight, the skin becomes dark. The body swells due to retention of water by the cells (oedema). Brain development and mental capacities are retarded, the liver too is damaged and the child often dies before the age of five. Millions of babies in Asia. Africa and Latin America suffer from this deficiency disease. In the absence of milk a protein rich diet obtained from animals or from soyabean or a combination of wheat, gram peanuts and jaggery can effectively cure this disease.

b.    hormones of the adrenal cortex or in the course of severe vomiting and acute diarrhea. This causes rise in heart beat rate, kidney, damage, weakness and paralysis of muscles.

Marasmus: Infants below the age of one year show a significant drop in body weight when breast feeding is replaced by less nutritive food, low in proteins and calories as a result of muscle degeneration, there is thinning of limbs and of the abdominal wall. The ribs look more prominent intestinal digestion is impaired, body growth and brain weight are lowered. Skin pigmentation and oedema are however absent. The disease can be cured by taking adequate amounts of proteins and carbohydrates.

Mineral Deficiency Disease

Some of them are:

a.    Anaemia: This results from insufficient iron in the diet; consequently, there is deficiency of hemoglobin in the Red Blood Corpuscles (RBC). Hence oxygen is not made available to cells to meet the metabolic requirements i.e. for oxidation of nutrients and production of energy, the person suffering from anaemia look pale, loose appetite and get fatigued easily. Eating meat liver green leafy vegetables such as spinach and fruits (banana, guava) helps in recovering from this ailment.

b.    Hypokalemia: Sometimes, severe loss of potassium occurs in the body due to excessive secretions of hormones of the adrenal cortex or in the course of severe vomiting and acute diarrhea. This causes rise in heart beat rate, kidney, damage, weakness and paralysis of muscles.

c.     Hyponatremia: An increased loss of sodium from the body, after intense vomiting and diarrhea, leads to dehydration, low blood pressure and even loss of body weight.

d.    Goitre: It is caused by deficiency of iodine. Consequently, the thyroid fails to secrete enough thyroxine. The absence or very low level of thyroxine steps up the production of Thyroid Stimulating Hormones (TSH) by the anterior pituitary, the increasing level of TSH brings about the enlargement of thyroid known as goitre. People living in areas with low iodine content in water are therefore advised to use iodized common salts containing 0.01% potassium iodide.

Vitamin Deficiency Diseases

(a)   Vitamin A: This is fat soluble and is commonly found in animal fat, milk, butter, and yellow fruits, such as papaya and mango, carrot and leafy vegetables. Its deficiency causes retarded growth, xerophthalmia (Dry eye, which is conducive to subsequent bacterial infection and eventual blindness), dermatosis or dry and scaly skin, night blindness, resulting from failure of the normal regeneration of visual purple after its lights induced charge i.e. on exposure to dazzling light one is not able to see in the dark or even in dim light.

(b)   Vitamin B Complex: The disease Beriberi is caused by the deficiency of thiamine, patients complain of extreme weakness, swelling and pain in the legs, loss of appetite, headache, shortness of breath, and even paralysis. By the deficiency of riboflavin (Vit. B2), resulting in blurred vision, burning and soreness of eyes and tongue, dermatosis and cracking of skin at angles of mouth the disease is called Ariboflavinosis. Inadequacy of niacin cause pellagra, in which the tip and lateral margins of the tongue, mouth and gums become red and swollen and later develop ulcers, the skin on hands, feet, elbows, wrists, and knees also become red and itchy and is peeled off causing pigmentation in patches. Deficiency of cyanoco-balamine (B12) affects the formation of RBC in the bone marrow; this leads to the reduction in the haemoglobin content of the blood, resulting in megaloblastic anaemia, Vit. B complex is a group of water-soluble vitamins present in nuts, liver milk, yeast, unpolished rice and unmilled pulses.

c.     Vitamin C: Lemons, oranges, grape fruits, tomatoes, guavas, mangoes, amlas, and uncooked green vegetables are rich sources of vitamin c or ascorbic acid. It’s deficiency leads to scurvy. Patients of scurvy exhibit symptoms of general weakness, pain in the joints, decline in weight and anaemia, the gums become spongy, swollen, and bleed easily, teeth become spongy, swollen, and bleed easily, teeth become loose and fragile, large dosages of ascorbic acids helps in combating common cold and certain vital infections.

d.    Vitamin D: Its deficiency causes rickets in children and osteomalacia in adults. Rickets occur due to loss of bone calcium, and results in softness and deformities of bones such as bow legs and pigeon chest. Enamel of teeth also becomes thin and shows pits. In osteomalacia, there is softness and pain in bones, which fracture easily. Adequate exposure to sunlight and supplementing food with liver, eggs, and cod liver oil help to avoid these ailments.

e.    Vitamin E: It is essential for the normal development of sperms. Deficiency of this vitamin causes sterility in rats, rabbits, and guinea pigs. Since the germinal epithelium degenerates. Immobile sperms are produced. The vitamin also acts as part of an enzyme system in preventing excessive cell oxidation, thereby preserving vitamin A and unsaturated fats.

f.     Vitamin K: The first observation that absence of this vitamin causes hemorrhage was made in 1929 while experimenting on chicks. The intestinal symbiotic bacteria of mammals produce this vitamin in sufficiency quantities. Vitamin K occurs in two forms-K1 and K2, the former occurring in many plants and the latter in fishmeal. The vitamin has a role in photosynthesis. It helps in coagulation of blood in higher animals by the release of Piothrombin into the blood.