About Nutrition

Nutrition is the science that interprets the nutrients and other substances in food in relation to maintenance, growth, reproduction, health and disease of an organism. It includes food intake, absorption, assimilation, biosynthesis, catabolism and excretion.

The diet of an organism is what it eats, which is largely determined by the availability and palatability of foods. For humans, a healthy diet includes preparation of food and storage methods that preserve nutrients from oxidation, heat or leaching, and that reduces risk of foodborne illnesses.

In humans, an unhealthy diet can cause deficiency-related diseases such as blindness, anemia, scurvy, preterm birth, stillbirth and cretinism or nutrient excess health-threatening conditions such as obesity and metabolic syndrome and such common chronic systemic diseases as cardiovascular disease, diabetes and osteoporosis. Undernutrition can lead to wasting in acute cases, and the stunting of marasmus in chronic cases of malnutrition.

Introduction To Nutrition:

Food is the prime necessity of life. The food we eat is digested & assimilated in the body and used for its maintenance & growth. Food also provides energy for doing work. Man has exhibited much thought & foresight in cultivating a variety of grains, fruits, vegetables,nuts and oil seeds and in rearing birds & animals for use of foods. Use of milk of different mammals  as food for infants has been practiced from very early times. A considerable amount of information is now available on the nutritive value of foods and nutritional requirements. 

Classification Of Nutrients:

Studies carried out by many scientists have shown that foods contain several chemical constituents which are known as nutrients. These are classified into two types : (1) micronutrients (2) macronutrients

Macronutrients are those nutrients that the body needs in large amounts. These provide the body with energy (calories). Micronutrients are those nutrients that the body needs in smaller amounts.

  • Macronutrients: Carbohydrates, Fiber, Fats, Protein, and Water.
  • Micronutrients: Vitamins, Minerals and others.

1. Macro Nutrients:


Carbohydrates may be classified as monosaccharides, disaccharides and polysaccharides

(A) Monosaccharaides

1. Biose (C2H4O2) Ex: Glycolic aldehyde

2 Trioses(C3H6O3) Ex: Glyceraldehyde dihydroxyacetone

3. Tetroses: (C4H8O4) Ex: Erythrose, Threose

4. Pentoses: (C5H10O5) Ex: Arabinose, Xylose, Ribose & Deoxyribose

5. Hexoses: (C6H12O6) Ex: Glucose, Fructose, Galactose

(B) Disaccharides: (C12H22O11)

Ex: sucrose, Lactose & Maltose

(C) Polysaccharides:

(1) Pentosans: Ex:Araban, Xylan

(2) Hexoses: (a) Starch, Dextrin, Glycogen

  (b) Cellulose, Inulin, Mannan, Galactan

(D) Complex polysaccharides:

Hemicelluloses, Gums, Mucilage’s and Pectin’s

They are classified depending on the number of monomer (sugar) units they contain. They constitute a large part of foods such as rice, noodles, bread, and other grain-based products, also potatoes, yams, beans, fruits, fruit juices and vegetables. Monosaccharides, disaccharides, and polysaccharides contain one, two and three or more sugar units, respectively. Polysaccharides are often referred to as complex carbohydrates because they are typically long, multiple branched chains of sugar units.

Traditionally, simple carbohydrates are believed to be absorbed quickly, and therefore to raise blood-glucose levels more rapidly than complex carbohydrates. This, however is not accurate.Some simple carbohydrates (e.g., fructose) follow different metabolic pathways (e.g., fructolysis) that result in only a partial metabolism to glucose, while in essence many complex carbohydrates may be digested at the same rate as simple carbohydrates. The World Health Organization (WHO) recommends that added sugars should represent no more than 10% of total energy intake.      


 The name “proteins” was suggested by MULDER in 1838 to the complex organic nitrogenous substances found inn animal and plant tissues.  Proteins constitute about one-fifth (20 percent) of the animal body on the fresh weight basis. They are essential for life processes. They play an important role in many biochemical, biophysical and bio-physiological processes in the body.


Protein is essential for growth and repair of the body and maintenance of good health. Protein also provides energy; 1 gram provides 17 kJ (4 kcal). The Reference Nutrient Intake (RNI) is set at 0.75g of protein per kilogram body weight per day for adults. The amount of protein we need changes during a lifetime.

Different foods contain different amounts and different combinations of amino acids (the building blocks of proteins). Protein from animal sources (e.g. meat, fish, eggs and dairy products) contains the full range of essential amino acids needed by the body. However, vegans and vegetarians can get all the amino acids they need by combining different plant sources of protein, e.g. pulses and cereals.


Proteins are large molecules formed  by the combination of a number of amino acids. About 21 amino acids have been found to occur in proteins. They are listed below:

Monoamino-monocarboxylic acids: These include glycine, alanine, valine, leucine, isoleucine, norleucine, serine and threonine.

Monoamino-dicarboxylic acids: These are aspartic acid and glutamic acid.

Diamino-monocarboxylic acids: Arginine and lysine belong to this group.

Sulphur containing amino acids: These are cystine, cysteine and methionine.

Aromatic and heterocyclic amino acids: These include phenylalanine, tyrosine, histidine, tryptophan, proline and  hydroxyproline.

The main type of linkage between the amino acids in the proteins molecule is the Peptide bond. In this linkage, the carboxyl group of one amino acid reacts with the amino group of another amino acid with the elimination of one molecule of water.

Classification Of Proteins

Proteins are classified as follows:

Simple proteins: 

These proteins are made up of amino acids only. e.g. albumins, globulins, prolamins, etc.

Conjugated proteins: 

These are complex proteins that are combined with the characteristic of non–amino acid substance called as a prosthetic group. These are of following types:–

Nucleoproteins: Combination of protein and nucleic acid

  • Mucoproteins: Combination of proteins and carbohydrates (>4%)
  • Glycoproteins: Combination of proteins and carbohydrates(<4%)
  • Chromoproteins: Combination of proteins and coloured pigments.
  • Lipoproteins: Combination of proteins and lipids.
  • Metalloprotein: Combination of proteins and metal ions.
  • Phosphoprotein: Combination of proteins and phosphate group.

Derived proteins: 

When proteins are hydrolyzed by acids, alkalies or enzymes, the degradation products obtained from them are called derived proteins.


Definition:  “Lipids are organic compounds that contain hydrogen, carbon, and oxygen atoms, which forms the framework for the structure and function of living cells.”

In biology and biochemistry, a lipid is a biomolecule that is soluble in nonpolar solvents.Non-polar solvents are typically hydrocarbons used to dissolve other naturally occurring hydrocarbon lipid molecules that do not (or do not easily) dissolve in water, including fatty acids, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides, diglycerides, triglycerides, and phospholipids.

 The functions of lipids include storing energy, signaling, and acting as structural components of cell membranes. Lipids have applications in the cosmetic and food industries as well as in nanotechnology.

Scientists sometimes define lipids as hydrophobic or amphiphilic small molecules; the amphiphilic nature of some lipids allows them to form structures such as vesicles,  multilamellar / unilamellar liposomes, or membranes in an aqueous environment.

Types Of Lipids:

Within these two major classes of lipids, there are several specific types of lipids important to live, including fatty acids, triglycerides, glycerophospholipids, sphingolipids, and steroids. These are broadly classified as simple lipids and complex lipids.

1. Simple Lipids:

Esters of fatty acids with various alcohols.

Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state.

Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols

2. Complex  Lipids:

Esters of fatty acids containing groups in addition to alcohol and a fatty acid.

Phospholipids : Lipids containing, in addition to fatty acids and alcohol, a phosphoric acid residue. They frequently have nitrogen-containing bases and other substituents, eg: in glycerophospholipids the alcohol is glycerol and in sphingophospholipids the alcohol is sphingosine.

Glycolipids(glycosphingolipids): Lipids containing a fatty acid, sphingosine, and carbohydrate.Other complex lipids. Lipids such as sulfolipids and amino lipids. Lipoproteins may also be placed in this category


Fiber, also known as roughage, is the part of plant-based foods (grains, fruits, vegetables, nuts, and beans) that the body can’t break down. It passes through the body undigested, keeping your digestive system clean and healthy, easing bowel movements, and flushing cholesterol and harmful carcinogens out of the body .


Water is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth’s hydrosphere, and the fluids of most living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients.



Vitamins are defined as organic compounds that are needed in small quantities to sustain life. Most vitamins need to come from food for maintenance of good health in human beings.

This is because the human body either does not produce enough of them or it does not produce any at all.


1. Fat Soluble Vitamins: Vitamins soluble in fat and fat solvents but insoluble in water.

The fat-soluble vitamins are A, D, E and K.

2. Water Soluble Vitamins: Vitamins soluble in water but insoluble in fats.

Water soluble vitamins include Vitamin C and the vitamin B complex: thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), Vitamin B6, biotin (B7), folic acid (B9), Vitamin B12. Vitamin A in its Beta-Carotene form is also water-soluble.


The body consists about 24 minerals, all of which must be provided by the diet. There are 16 essential minerals: calcium, phosphorus, potassium, sulfur, sodium, chloride, magnesium, iron, zinc, copper, manganese, iodine, and selenium, molybdenum, chromium, and fluoride .

Some of the non-essential minerals are:

  • Aluminum.
  • Antimony.
  • Arsenic.
  • Barium.
  • Beryllium.
  • Bromine.
  • Cadmium.
  • Cerium.