The human body needs materials to build and repair body tissues for proper nutrition and health.  Foods vary in the amount of energy they contain and people vary in the amount of fuel they need. The fuel value of food is measured in units called calories.  The more active a person is, the more calories he needs top maintain his current weight.  Good nutrition is obtained from a balanced diet, from the daily intake of the proper kinds and amounts of food.  Nutrition is concerned with the study of and its relation to health. The lack of proper foods or proper amounts of food in the diet results in malnutrition.