Nutrition is the science of food and the nutrients and other substances contained in food. Nutrients are the necessary constituents of food required by an organism. Nutrients are divided into two (i) Macronutrients: include carbohydrates, proteins and lipids and (ii) Micronutrients: which include minerals and vitamins. Each nutrient plays a special role. Fibre is not a nutrient but is being considered as a necessary food component. The energy expenditure by an individual depends on: the basal metabolic rate (BMR), the thermo genic effect (Specific dynamic action, SDA) of food, physical activity and environmental temperature. A balanced diet is defined as one which contains a variety of foods in such quantities and proportions that the need for energy, amino acids, vitamins, minerals, fats, carbohydrates and other nutrients are adequately met for maintaining health, vitality and general well being and also makes a small provision for extra nutrients to with stand short duration of illness. The most common nutritional disorders due to under nutrition are protein energy malnutrition (PEM) caused by protein and energy deficiency. PEM can be classified as marasmus and kwashiorkor. Obesity is attributed to the over nutrition.