Nutrient Composition of Food

  • Food can be classified into:
    1. Energy-giving food-------- Carbohydrates and fats
    2. Body Building Food -------Proteins
    3. Protective Food-------------Minerals and Vitamins
  • Carbohydrates, proteins, fats, vitamins, minerals, water and roughage are seven essential components of the diet.
  • Carbohydrates, proteins and fats are significant nutrients called macronutrients or proximate principles of food, whereas vitamins and minerals are called micronutrients or protective principles of nutrition.
  • Carbohydrates and fats are energy producers.
  • Protein is a bodybuilder. It is essential for body growth and the repair of tissues.
  • Vitamins and minerals are mainly metabolic regulators. Minerals and vitamins are in the form of small molecules, and many of them need no digestion.

1. Carbohydrates

  • Carbohydrates are the primary products of photosynthesis.
  • Most carbohydrates contain only three elements, viz. carbon, hydrogen and oxygen. The general formula of carbohydrates is Cx(H2O)y.
  • One gram of glucose yields about 4.2 kilocalories of energy.
  • Carbohydrates contribute about 45% of calories to most diets.
  • The basic unit in a simple sugar molecule (monosaccharide) is glucose (C6H12O6). Glucose is the simplest carbohydrate which is an instant source of energy.
  • The human body can use carbohydrates only in the form of monosaccharides.
  • Based on sugar molecules, carbohydrates are divided into three categories:
    1. Monosaccharides are formed of only one sugar molecule, e.g., glucose, galactose, and fructose.
    2. Oligosaccharides are formed of two to ten mono sugars interlinked by glycosidic bonds. The most common oligosaccharides are disaccharides (double sugar) e.g. maltose (glucose + glucose), sucrose (glucose + fructose) and lactose (glucose +galactose).
    3. Polysaccharides: these are formed of much mono sugar interlinked by glycosidic bonds. e.g., cellulose, starch, glycogen, chitin, hyaluronic acid and heparin.
  • Fructose is the sweetest sugar among naturally occurring sugars.
  • Lactose or milk sugar is found in milk. Human milk contains more lactose than the milk of cows, buffalo and goats.
  • Starch (common in plants) and glycogen (common in animals) are two food storage polysaccharides.
  • Cellulose and chitin are two structural polysaccharides. Cotton fibers contain the most significant amount (90%) of cellulose among natural materials.

2. Fats:

  • fats are esters of fatty acids with glycerol. The general formula of fat is C57H110O6.
  • On average, an adult needs about 75-110 grams of fats.
  • Like carbohydrates, fat contains carbon, hydrogen and oxygen atoms.
  • 1gram of fat gives 9.3 kilocalories on complete combustion, about 2.25 times more than the energy provided by the same amount of glucose.
  • Fats are found in adipose tissues. The fat cells of fatty tissue can store up to 95% of their volume of triglycerides (fats), and hence adipose tissues are often called the Fat Depot of the body.
  • Fats are a mixture of lipids (triglycerides).
  • The lipid mixture (fat) is solid at 20°C.
  • Essential fatty acids cannot be synthesized in the body and must be present in the diet. These include linoleic acid, linolenic acid and arachidonic acid.
  • Non-essential fatty acids can be synthesized in the body and may not be present in the food. These include palmitic acid, stearic acid, etc.
  • Fats that are generally liquid at room temperature are called oils.
  • Fatty acids are of two types, viz. saturated and unsaturated.
  • If fats do not have any double bond between the carbons of molecular chains, they are called saturated, e.g., palmitic acid and stearic acid.
  • If they have one or more double bonds between the chain's carbon, they are called unsaturated fatty acids, e.g., oleic acid.
  • Unsaturated fatty acids are found in fish oil and vegetable oil.
  • Vegetable fats are highly unsaturated, whereas animal fats are saturated.
  • Coconut oil palm oil is the only saturated vegetable oil. Most of the saturated fat is animal fat. Saturated fat is also solid, e.g., butter.
  • Excess intake of saturated fats enhances blood cholesterol levels. Cholesterol is a steroid that reinforces the cell membrane structure in animal cells. Cholesterol is known to cause arteriosclerosis (thickening of the wall of arteries), high blood pressure and heart diseases.

3. Proteins:

  • Protein contains carbon, hydrogen, nitrogen and oxygen and, less commonly, sulfur, phosphorous, iodine and iron.
  • Proteins are primary foodstuffs and are made up of amino acids.
  • All amino acids have a basic skeleton consisting of carbon linked to an amino group (NH2), a carboxyl group (COOH) and a hydrogen atom (H).
  • A covalent bond called peptide bond forms between the amino group of one amino acid and the carboxyl group of another amino acid.
  • Protein is synthesized on the ribosome as a linear sequence of amino acids held together by peptide bonds.
  • Peptide usually refers to a molecule composed of a short chain of amino acids, such as dipeptide (two amino acids), tripeptide (three) and tetrapeptide (four).
  • A polypeptide contains an unspecified number of amino acids but usually has more than 20. It is often a smaller subunit of protein.
  • A protein is the largest of this class of compounds and usually contains a minimum of 50 amino acids.
  • Excess amino acids can not be stored in the body.
  • Protein is essential; for the growth and replacement of cells. Thus, proteins are necessary for body growth and functioning.
  • Proteins regulate metabolism. They make 12-15% of diet calories.
  • The complete hydrolysis of protein yields about 20 different amino acids. It means protein occurs naturally in about 20 forms.
  • Out of 22 amino acids required, 9 for adults and 10 for children are supplied in the diet form outside as they are not synthesized in the body. These are known as essential amino acids. The remaining amino acids are synthesized by the body itself.
  • 1 gram of protein liberates 4.2 kilocalories of energy.
  • Proteins from the most critical molecule in nature.
  • Proteins provide a base for manufacturing enzymes, hormones, antibodies, etc.
  • Proteins that contain most of the essential amino acids are termed first-class proteins, while those which do not are called second-class proteins.
  • Animal proteins are first-class proteins, and plant proteins are second-class proteins.
  • Casein is a protein that forms part of the food for young animals. The best source of casein is milk.
  • Protein deficiency causes Kwashiorkor (red-haired body) and Marasmus in infants.
  • Sources of proteins are milk, eggs, fish, meat, pulses, soybean and legumes.

4. Water

  • water usually forms 75-90% of cytoplasm.
  • 70 to 90 percent of living cells are in the water.
  • In humans, about two-thirds of the body is formed of water and of these, about 55 percent (20-22 liters) is confined to cells as intracellular water. The remainder is found in extracellular fluids like blood, tissue fluid and lymph.

5. Minerals

  • Minerals are inorganic substances.
  • At least 29 elements are found in our bodies.
  • Minerals have no energy value but the imbalance of mineral levels in the body may cause diseases.
  • In human nutrition, the dietary bulk mineral elements (RDA > 200 mg/day) are:
    1. Calcium
    2. chlorine
    3. magnesium
    4. Phosphorous
    5. Potassium
    6. Sodium
    7. Sulphur
    8. Trace Minerals
  • The most important trace mineral elements (RDA < 200mg/day) are:
    1. Chromium
    2. Cobalt
    3. Copper
    4. Fluorine
    5. Iodine
    6. Iron
    7. manganese
    8. molybdenum
    9. Selenium
    10. Zinc

Calcium and Phosphorus:

  • Calcium and phosphorous are deposited in bones and teeth to give them strength and rigidity.
  • Calcium (Ca++) helps in blood coagulation, neuromuscular function, cardiac function and actions of many enzymes and hormones.
  • Calcium plays an essential role in sustaining intestinal peristalsis and the growth of body tissues.
  • Calcium is needed for normal muscle and nerve function.
  • Phosphorous helps in maintaining the constant composition of the body fluids.
  • Phosphorous enters into many compounds such as nucleic acids and phospholipids, many coenzymes and high-energy compounds like ATP.

Sodium, Potassium and Chlorine:

  • Sodium (NA+) is the principal mineral cation in the extracellular fluid (fluid outside the cell).
  • Potassium (K+) is the principal cation inside the cell (inside the cytoplasm of the cell).
  • Chlorine (Cl-) is the principal mineral in extracellular fluid.
  • Na+ and K- are essential for maintaining water balance and acid-base balance and also important in nerve impulse transmission.


  • Magnesium is required as a catalyst for many intracellular enzymatic reactions.
  • Low magnesium concentration causes increased irritability of the nervous system and peripheral vasodilation.
  • Potassium and Magnesium are required for proper muscular contraction.


  • Iron is required for hemoglobin and cytochrome synthesis.
  • Iron gives the red color to RBC.
  • Iron is essential for both transportations of oxygen to tissues and for the operation of oxidative systems within the tissue cells.


  • Fluorine maintains normal dental enamel and prevents dental cavities.
  • If fluorine is more minor than 1mg/L in water, it causes dental activities.
  • If fluorine is more significant than 1.5 mg/L in water, it causes fluorosis, represented by mottled teeth and enlarged bones.


  • Cobalt helps in erythropoiesis and in the activities of some enzymes.


  • Zinc helps in the healthy functioning of the tongue.
  • Zinc helps in CO2 transport.
  • Zinc is essential for the digestion of proteins in the alimentary canal.
  • Zinc is a component of at least 70 enzymes like carbonic anhydrase and some peptidases.


  • Copper helps in the utilization of iron.
  • Coppe deficiency may produce anemia.


  • It is the component of hormones e.g., insulin.
  • It is necessary for normal metabolism.


  • Iodine is essential for the formation of the thyroxine hormone, which is secreted by the thyroid gland.
  • The deficiency of iodine causes Goitre.

6. Vitamins

  • C. Funk coined the term 'Vitamin' in 1911.
  • Vitamins are micronutrients, biological regulators and metabolic regulators.
  • Vitamins are organic compounds needed in small quantities.
  • Vitamins cannot be synthesized in the body except vitamin D and vitamin K, which can be synthesized in the body.
  • There are about 30 different types of vitamins described so far.
  • Vitamins are generally divided into two groups:
    1. Fat-soluble vitamins (A, D, E and K): If these are taken in excess, they cause a condition known as hypervitaminosis (cause of hair cracked mouth).
    2. Water-soluble vitamins (B, C and P): If water-soluble vitamins are taken in excess, they are washed away.

Vitamin A (Retinol):

  • It was discovered by Mc Collum Davis but was isolated by holmes.
  • It is known as an anti-infection vitamin.
  • It can be synthesized in the liver from yellow and red carotenoid pigments.
  • It forms the retinal pigments such as rhodopsin of rod cells and iodopsin of cone cells of the retina.
  • It is required for the average growth of children.
  • It maintains normal, living secretory epithelia in mucous membranes and glands.
  • Sources of vitamin A are carrot, fish liver oils, milk, green vegetables, cod liver oil, egg yolk, ghee, butter, tomatoes, papaya, guava, etc.
  • Its daily requirement is about 2 mg.
  • The deficiency of Vitamin A causes diseases like Nyctalopia (Night blindness) and Xeropthalmia.

Vitamin B-Complex

B1 (Thiamin or Thiamin)

  • Vitamin B1 is essential for a healthy nervous system and mucous membrane.
  • It is essential for the metabolic process.
  • Vitamin B1 helps in the formation of the cocarboxylase enzyme involved in decarboxylation (citric acid and cycle).
  • The richest source of Vitamin B is whole wheat bread. Sources are cereals, pulses, and green leaves.
  • The deficiency of Vitamin B1 checks growth in children and causes diseases like beriberi (which affects the peripheral nervous system) and polyneuritis.

B2 (Riboflavin):

  • Vitamin B2 combines in the tissue with phosphoric acid to form two coenzymes, Flavin Mononucleotide (FMN) and Flavin Adenine Dinucleotide (FAD).
  • The yellow color of cow milk is due to the presence of riboflavin.
  • Sources of vitamin B2 are cheese, eggs, yeasts, etc.
  • Deficiency of vitamin B2 causes dermatitis, sore mouth, ulceration and chellosts (disorder, sore mouth, ulceration and chellosts (a disorder of lips and mouth) characterized by scales and fissures, skin becomes rough and red, diarrhea (digestive upsets).

B3 (Pantothenic Acid):

  • Pantothenic acid, also called vitamin B3, is a water-soluble vitamin required to sustain life.
  • Pantothenic acid is needed in the metabolism and synthesis of carbohydrates, proteins and fats.
  • Chemically, it is the amide between D-pantoate and beta-alanine. Its name is derived from Greek pantothen meaning from everywhere and small quantities of pantothenic acid are found in nearly every food, with high amounts in whole grain cereals, legumes, eggs, meat and royal jelly.
  • It is commonly found as its alcohol analog, the provitamin panthenol and as calcium pantothenate.
  • In humans, its deficiency causes burning feet syndrome.

B5 (Nicotinic Acid or Niacin):

  • Vitamin B5 is also called as Antipellagra Vitamin or Pellagra preventing factor because deficiency of B5 causes Pellagra.
  • Pellagra is common in those areas where maize is the staple food item.
  • Primary vegetable sources are cereal husk, peas, beans and green leafy vegetables, while primary animal sources are liver, fish, milk, egg yolk, etc.
  • Pellagra can be featured in dermatitis, dementia, i.e., memory disorder, diarrhea and death. Hence, it is also known as a 4-D syndrome.

B6 (Pyridoxine):

  • It exists in the form of pyridoxal -phosphate in the cell and functions as a coenzyme.
  • It helps in the transmission process for the synthesis of amino acids.
  • The deficiency of vitamin B6 causes dermatitis, anemia, and convulsions in children.
  • It is helpful during radio therapy.

B7 (Biotin):

  • It is a sulfur-containing coenzyme.
  • It is essential for fat synthesis.
  • It is also known as vitamin H.
  • The deficiency of vitamin B7 causes muscular pains, dermatitis and growth failure.

B9 (Folic Acid):

  • It is abundantly present in green leafy vegetables like cabbage.
  • Its daily requirement is about 0.4mg.
  • Its acts as a coenzyme for the synthesis of those proteins which are essential for the formation and maturation of RBCs.
  • It promotes the synthesis of Thymidine monophosphate and DNA.
  • Its deficiency causes macrocytic or megaloblastic anemia and sprue (mouth ulceration) in men.
  • It is also known as vitamin M.

B12 (Cyanocobalamin):

  • It is a cobalt-containing vitamin.
  • It is found in animal proteins such as meat, liver and fish.
  • It is the only vitamin not found in vegetables.
  • It acts as a coenzyme for reducing ribonucleotides to deoxyribonucleotides.
  • It promotes DNA synthesis, maturation of RBC and myelin formation.
  • It promotes DNA synthesis, maturation of RBC and myelin formation.
  • Deficiency of vitamin B12 causes pernicious anemia (failure of RBC maturation) and degeneration of the spinal cord to ataxia leading to paralysis.

Vitamin C (Ascorbic acid):

  • This is the earliest known vitamin.
  • Vitamin C is rapidly destroyed by heat and decreases with time.
  • It is absent in milk, egg and bread.
  • Excess vitamin C is generally exercised in urine.
  • It promotes wound healing.
  • It helps in the absorption of iron and provides resistance to cold.
  • Smokers and chronic alcoholics suffer from deficiency of this vitamin.
  • The deficiency of vitamin C causes scurvy (spongy and bleeding gums).
  • Sources of vitamin C are all citrus fruits, predominantly almond, orange and lemon and green pepper.

Vitamin D (Calciferol):

  • Vitamin D refers to a group of fat-soluble prohormones, the two primary forms of which are vitamin D2 (or ergocalciferol) and vitamin D3 or cholecalciferol. the term vitamin D also refers to metabolites and other analogs of these substances. Vitamin D3 is [produced in skin exposed to sunlight, specifically ultraviolet B radiation. very few foods are naturally rich in vitamin D, and most vitamin D intake is in the form of fortified products, including milk, soya milk and cereal grains.
  • Vitamin D regulates the calcium and phosphorous levels in the blood by promoting their absorption from food in the intestines and by promoting the reabsorption of calcium in the kidneys.
  • It promotes bone formation and mineralization and is essential in the development of an intact and strong skeleton.
  • It inhibits parathyroid hormone secretion from the parathyroid gland.
  • Vitamin D affects the immune system by promoting immunosuppression and anti-tumor activity.
  • Vitamin D deficiency can result from inadequate intake coupled with inadequate sunlight exposure. These disorders limit its absorption, conditions that impair the conversion of vitamin D into active metabolites, such as liver or kidney disorders, or rarely, the number of hereditary disorders. Deficiency results in impaired bone mineralization and leads to bone softening diseases, rickets in children and osteomalacia in adults and possibly contributes to osteoporosis.
  • Vitamin D is synthesized in the skin by cholesterol by UV light.
  • It regulates the absorption and utilization of calcium and phosphorous.
  • It is also known as sunshine vitamin or antirickets vitamin.
  • Good source of obtaining vitamin D is meat, liver, and milk.
  • Cod liver oil and shark liver oil are good sources of both vitamin A and vitamin D.

Vitamin E (Tocopherols or Tocotrienol):

  • It is commonly called anti sterility vitamin or beauty vitamin.
  • It inhibits peroxide formation and thereby prevents the damage of membrane lipids.
  • Vitamin E removes scars and wrinkles from the skin.
  • Vitamin E deficiency diseases are sterility (impotence) and muscular atrophy.
  • Sources of vitamin E are wheat, animal food, vegetable cotton seeds oils, green leafy vegetables etc.
  • Its daily requirement is about 15 mg.

Vitamin K (Phylloquinone or Naptthoquinone):

  • It is synthesized by bacteria in the colon. It is essential for blood clotting.
  • It is essential for the synthesis of prothrombin in the liver.
  • It is commonly called Anti hemorrhagic vitamin.
  • The deficiency of vitamin K causes uncontrolled bleeding (no coagulation or clotting).
  • Sources of vitamin K are green plants, cabbage, cauliflower, spinach, etc.
  • It was discovered by Danish Scientist Dam in 1935.

Vitamin P (Hesperidin):

  • It helps in maintaining average capillary resistance.
  • The deficiency of vitamin P may cause internal bleeding.
  • Sources of vitamin P are green vegetables and citrus fruits.

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