Calories are a way of measuring the potential energy in foods. They also measure the amount of energy, in units, that the body uses. Food supplies calories to the body. The body burns calories to stay alive and to move. The nutrients that provide calories in food are limited to fat, protein, and carbohydrates. These 3 nutrients can be found in foods in all of the major food groups. Foods may have one or more of these nutrients. Even though it is not a nutrient, alcohol has calories as well.
Carbohydrates, proteins, and fats all provide energy to the body in the form of calories. These nutrients are released from foods during digestion. Then they are absorbed into the blood stream and changed to glucose, which is another name for blood sugar. Glucose is what the body actually uses as energy.
Energy that the body does not need immediately is stored, some of it as fat. The rest is stored in the liver and muscles as glycogen, which is the stored form of glucose. The body can use these stores at a later time for energy.
Each nutrient provides different amounts of calories per gram to the body. One gram of carbohydrate equals 4 calories.One gram of protein equals 4 calories.One gram of fat equals 9 calories.One gram of alcohol equals 7 calories.
These figures are used to calculate calories per serving. If a food is made of only fat, and contains 9 grams of fat, the calories in the product equals: 9 grams fat x 9 cal/gram of fat = 81 calories. On the other hand, if the food contained 2 grams of fat and 4 grams of protein, the total calories would equal 34 (2 grams fat x 9 cal/gram = 18 calories plus 4 grams protein x 4 cal/gram = 16 calories, for a total of 34 calories).
Food offers more than just calories. It offers vitamins, minerals, and water, which are also key nutrients in maintaining health. These nutrients do not supply calories, however. When foods supply mainly calories and few nutrients, they are known as "calorie-dense." When foods supply calories along with vitamins and minerals, they are known as "nutrient-dense."
The key is to choose your calories wisely. Choose foods that will provide a good balance of both calories and nutrients. For a healthy diet, people need all 3 nutrients in their daily diet. Federal dietary guidelines are issued by the US Department of Agriculture and the Department of Health and Human Services. These guidelines recommend a diet that gets most of its calories from whole grain products, fresh vegetables and fruits, lowfat milk products, lean meats, fish, poultry, and dried beans.
The Food Guide Pyramid acts as a tool to help individuals follow these dietary guidelines. In addition, the American Heart Association recommends a diet where: carbohydrates supply 55 to 60% of the caloriesfat calories make up less than 30% of the total (with less than 10 % from saturated fat)
The body's need for energy and fuel never stops. Each person needs a certain amount of calories to fuel the body. The specific amount of calories depends on many factors. These include: weightheightbasal metabolic rate, abbreviated as BMR, which is how many calories the body burns at rest in 24 hoursagebody composition, which refers to how fat and muscle are distributed in the bodyphysical condition and activity level
Once a person is an adult, energy, which means calorie, needs drop 2% for each decade of age. Eating more calories than are needed usually results in weight gain. Eating less than the required calories usually results in weight loss.
Active men and teenaged boys need about 2,800 calories a day to fuel their bodies enough. Exact calorie needs for each person depends on the factors listed above.
Following the Food Guide Pyramid (www.mypyramid.gov), for this group, 2,800 calories would equal about: 10 servings from the bread group7 servings of vegetables5 servings of fruit2-3 servings from the milk group (teens should have 3 servings)3 servings (for a total of 7 ounces) from the meat group
Active women, teenaged girls, children, and less active men need about 2,200 calories to fuel their bodies well. Following the Food Guide Pyramid, for this group, 2,200 calories equate to: 7 servings from the bread group6 servings of vegetables4 servings of fruit2-3 servings from the milk group (pregnant and breastfeeding women should get 3 servings, teenaged girls and young adults up to age 24 should get 4 servings)2 servings (for a total of 6 ounces) from the meat group.
Less active women and some older adults need about 1,600 calories to fuel their bodies. Following the Food Guide Pyramid, for this group, 1,600 calories would equate to: 5 servings from the bread group4 servings of vegetables3 servings of fruit2-3 servings from the milk group2 servings (for a total of 5 ounces) from the meat group
Amercian Council on Exercise. (1996). Lifestyle&Weight Management Consultant Manual. Editors: Cotton, R., Ekeroth, C.: San Diego, California.
Duffy, R., MS, RD, CFCS (1996). The American Dietetic Association's Complete Food&Nutrition Guide. Minesota: Chronimed Publishing.
Miller, Gregory; Jarvis, Judith and McBenan, Lois. (2000). Handbook of Dairy Foods and Nutrition. 2nd.ed. Florida: CRC Press.