There are three types of substances present in the food. They are
- Carbohydrates are the primary products of photosynthesis. They are the most important energy providing substrates for animals.
- Most carbohydrates contain only three elements, viz., carbon, hydrogen and oxygen.
- The simplest carbohydrates are monosaccharides. This may be hexose, pentose or triose sugars.
- Hexose sugars are mainly three isomers namely glucose, fructose and galactose.
- Pentose sugars are mainly ribose and deoxyribose sugars in RNA and DNA.
- Triose sugars are formed during metabolism like glyceraldehyde.
- Three common disaccharides are : Maltose (Glucose + glucose), Sucrose (Glucose + Fructose) and Lactose (Glucose + Galactose)
- Sucrose is the cane sugar found in sugarcane. Sucrose does not reduce Cu++ to Cu+.
- Maltose or malt sugar is formed during germination of starch seeds.
- Lactose or milk sugar is found in milk.
- Comparing to the milk of cow, buffalo and goat, lactose is highest in human milk.
- Starch common in plants and glycogen in animals are two food storage polysaccharides.
- Starch is found abundantly in rice, wheat, legumes, potato, bananas, etc.
- Our food mostly contains carbohydrates.
- Rice and potato are good source of carbohydrates.
- Also read about Digestive system
- Proteins are among the most important macromolecules of organisms.
- After water, proteins form the major (14%) part of living protoplasm. Of the dry weight of protoplasm, 75% is the protein.
- Proteins ae very complex organic molecules containing carbon, hydrogen, oxygen and nitrogen and less commonly sulphur, phosphorus, iodine and iron.
- The term 'Protein' was coined by Berzelium and Mulder.
- Fischer and Hof meister discovered that on complete hydrolysis all protein molecules break down into simpler amino acids.
- Basic unit or smallest structural units of proteins are called amino acids. Amino acids are linked together in long chain to form protein.
- The anhydrobonds of proteins are called peptide bonds. A peptide bond is formed between carboxyl group of one amino acid and amino group of adjacent.
- Proteins in our body may be circulated in the form of amino acids. The excess of amino acids cannot be stored in the body.
- Although about 300 amino acids occur in nature, only 20 of these enter into the composition of proteins.
- Amino acids that cannot be synthesized in the body are called essential.
- Essential amino acids are those which are taken from food, not synthesized in the body.
- Other amino acids may be synthesized in the body, particularly from carbohydrate metabolites. They need not be supplied in the diet and are called non-essential or dispendable amino acids.
- Proteins which contain most of the essential amino acids are termed first class, while those do not, are called second class.
- Animal proteins are mostly first class and plant proteins are second class proteins.
- Casein is a protein which forms the part of food for the young animal. Best source of casein is milk.
- Many children in our country suffer from malnutrition, a protein deficiency disease known as Kwashiorkor disease. This can be prevented by giving food rich in protein.
- A person suffering from Kwashiorkor should have more meat, butter, milk and eggs in his diet.
- Glutelins are large globular proteins present in the wheat or rice.
- Haemoglobin and cytochromes are two chromoproteins.
- Fats are esters of fatty acids with glycerol.
- Each molecule of glycerol can react with three molecules of fatty acids.
- Depending on the number of fatty acids that are attached to the glycerol molecule, the esters are called mono-, di- or triglycerides.
- Fats that are generally liquid at room temperature are called oils.
- Fatty acids most commonly involved in fat formation are: Palmitic, stearic and oleic acids.
- Fatty acids are called saturated if they do not have any double bond between the carbons of molecular chains, eg., palmitic acid (16C) and stearic acid (18C)
- Unsaturated fatty acids have one or more double bonds between the carbons of the chain, eg., oleic acid with one double bond.
- Essential fatty acids are some polyunsaturated fatty acids (with more than one double bond) which cannot be synthesized in the animal body and must be supplied with food to avoid their deficiency.
- Linoleic, linolenic and arachidonic acids are essential fatty acids for man.
- Excess intake of saturated fats like butter, ghee and hydrogenated vegetable fats enhances blood cholesterol level.
- High amounts of fats, particularly saturated fats and cholesterol should be avoided by sedentary, old or obsese persons and patients of heart disorders and high blood pressure.
- Too much use of fats should be avoided during summer months.
- Fat yields twice as many calories per gram as carbohydrates.
- Fats are richly found in adipose tissues.
- Obesity can be controlled by reducing intake of calories from fats and carbohydrates.