Foods provide human beings with the energy needed to perform vital functions. This energy is measured in kilocalories, defined as the amount of energy or heat required to raise the temperature of 1 kilogram of water by 1 degree Celsius. In general use, the term calorie is normally substituted for kilocalorie.
There is a direct correlation between calories consumed and body weight. Calorie intake needs to equal calorie expenditure in order for a person to maintain weight. Consuming more calories than expended will result in weight gain, while consuming fewer calories than expended will cause weight loss.
Although foods consist of many components, calories come from only four sources: carbohydrates, proteins, fats, and alcohol. Carbohydrates and proteins contain 4 calories per gram, fats have 9 calories per gram, and alcohol carries 7 calories per gram. Therefore, a food containing 10 grams of fat will contain 90 calories from fat.
Any food source that has a good supply of nutrients in relation to the number of calories it contains is considered nutrient-dense. Whole grains, fresh fruits and vegetables, lean meats, poultry, and low-fat dairy products are all nutrient-dense foods. Foods and beverages that contribute little or nothing besides calories include beer, wine, and other forms of alcohol, doughnuts, jams and jellies, and candy.
In order to maintain good health, the United States Department of Agriculture (USDA) recommends that 55 to 60 percent of a person's daily calorie intake should come from carbohydrates, and protein should contribute 12 to 15 percent. Fat calories should be limited to a maximum of 30 percent.
The Professional Chef, 7th Edition by The Culinary Institute of America