The survival of all living organisms is due to several types of nutritive processes. The process of nutrition involves ingestion digestion, absorption and assimilation of food materials. The composition of nutrients vary in different types of feeding. However, for all living organisms, the nutrient comprises the following organic and inorganic components. They are carbohydrates, proteins, lipids, vitamins, minerals and water. Each component has a specific functional role. A well proportioned intake of nutrients depends on several factors such as stage of growth, sex, health condition, bodily activities and environmental situations.
Along with complex organic substances, such as carbohydrates proteins and lipids, our body needs substances such as minerals, vitamins and water as accessory food factors.
Of the minerals certain elements are found in greater concentration. They are sodium, calcium, potassium, magnesium, phosphorus, sulphur and chlorine. Certain other minerals are required in slightly lower concentration for performing useful functions. These include, iron, copper, zinc, cobalt, manganese, iodine and fluorine(trace elements). Of these minerals, larger portion of certain minerals are concerned with body building activities such as formation of bones and teeth (Calcium, Magnesium and Phosphorus). Trace elements and other minerals are useful in physiological activities such as oxygen transport (Iron), hormone synthesis (Iodine) and intermediary metabolism (Manganese, Copper, Zinc). Some of the elements remain as constituentsof the body fluids (Chlorine, Sodium and Potassium). Presence of certain minerals is essential for neuro-muscular irritability (Magnesium, Sodium and Potassium), blood clotting (Calcium), cardiac functions (Potassium and Calcium).
Water is a major costituent in the body of all mammals. The proportion of water in the lean body mass (mass of the body - fat content) is constant at around 71 to 78 % in animals including human beings.
The total body water content varies with age, sex and body weight. In a new born child it is 85 to 90 % of body weight. In young adults it ranges from 55 - 60 %.
Of the total body water, about 2/3 is found as intra-cellular fluid (ICF) and 1/3 as extra-cellular fluid (ECF). About 25% of ECF is the plasma of blood.
The body water content is kept constant by maintaining a proper balance between water intake and loss. Intake of water happens through drinking of water and beverages, water in the food consumed and water generated during metabolism. The average water intake is around 2500 ml/ day (as water 1400 ml).
Water loss happens through four routes. They are
1. Urine (about 1400ml),2. Expiration (400ml), 3. Through skin (600ml), 4. Loss in faeces (100ml)
1. It is an essential constituent of all the cells of the body.
2. It serves as a transport medium for nutrients and excretory products.
3. It serves as a site for chemical reactions.
4. It is a valuable solvent for electrolytes, enzymes, hormones and vitamins.
5. It plays a vital role in the maintenance of body temperature.
6. It helps to maintain form and texture of tissues.
A balanced diet must have all food supplements in needed proportion. It should be preferred in such a way that normal growth. working capability, nitrogen balance and full calorie requirement can be maintained. While planning a balanced diet, the total calorie requirement of the individual is calculated and then the different components of the food are selected. Normally the calorie content of the food is fixed with an understanding that 10 -15 % of calories are to be obtained from proteins, 25 - 30% from fats and the rest from carbohydrates.
In nutrition and dietetics a calorie means the amount of heat required to raise 1 Kg water by 10C. As per the Nutrition Expert Committee of ICMR (1968) the calorie requirements are prescribed for Indian Reference Man (IRM) and Woman (IRW). The IRM and IRW have following characteristics.
IRM :- 25 years of age, 1.62 sq.mt of body surface, 55 kg body weight and remains healthy.
IRW :- 25 years of age, 1.4 sq.mt of body surface, 45 kg body weight and remains healthy.
The calorie requirement for IRM and IRW depending on their nature of work is prescribed as follows
Daily activities Sedantary Moderate Heavy
work work work
A. Basal metabolism (BMR) 460 calories 460 calories 460 calories
(8 Hrs of Sleep)
B. Non occupational 1220 calories 1220 calories 1220 calories
activities (8 Hrs)
C. Occupational 750 calories 1100 calories 2200 calories
activities (8 Hrs)
Total 2430 calories 2780 calories 3880 calories
A. Basal metabolism 354 calories 354calories 354 calories
(8 Hrs of sleep)
B. Non occupational 826 calories 826calories 826 calories
activities (8 Hrs)
C. Occupational 610 calories 900calories 1800 calories
activities (8 Hrs)
Total 1790calories 2080calories 2980calories
While formulating and planning the diet for a person, his/her calorie requirement is assessed. This assessment is based on the requirement of IRM and IRW. It is adjusted according to age, weight, health and working conditions. Final prescription of food is provided based on the calorie value of each item of food. Due attention is given also for palatability and social food habit. Balanced diet for Indian adult male and female doing moderate work.
Obesity is the storage of excess of body fat resulting in a significant impairment of health from a variety of diseases, notably hypertension, atherosclerotic heart disease and diabetes. A level of 10% above the standard weight, for subjects of same age and sex, is considered as obese.
The degree of obesity is assessed by the body mass index (BMI). It is calculated as weight in Kg divided by the square of height in meters. For example, a 70 Kg person with a height of 180 cms would have a BMI of 21.6 (70/1.82). Normal BMI range for adults is 19 - 25. Men and women having BMI values above this range are considered obese
Obesity may be due to genetic reasons, increased appetite leading to excessive intake of food than is needed by the body, endocrine causes and / or metabolic disorders.