Every function of the body requires energy; energy sustains metabolism, physical work, nerve transmission, respiration and circulation, and the body's core temperature. Macronutrients are the components of food that supply energy or calories. They include carbohydrate, fat, and protein. Carbohydrate and protein have 4 cal/g and fat 9 cal/g. Alcohol also supplies energy and has 7 cal/g, but usually it is excluded from the macronutrient group because it supplies no essential nutrients. The function of supplying energy differentiates macronutrients from micronutrients, which include vitamins and minerals.

Expressed simply, there are 2 basic reasons to consume macronutrients: (1) to provide adequate intake of the essential nutrients needed to support the body's functions and (2) to provide appropriate amounts of nutrients to support health and prevent chronic disease. ...