For every physical activity, the human body requires energy and the amount depends on the duration and type of activity. Energy is measured in Calories and is obtained from the body stores or the food we consume. This chapter deals with different components of our diet and their importance to the human body. Carbohydrates, proteins and fat give 4, 4 and 9 calories respectively per gm when they oxidized. Dietary fiber is another important component of our diet which plays a major role in protecting humans from diseases. Kwashiorkor and marasmus are the two major types of protein calorie malnutrition seen in malnourished children.