What Is Basal Caloric Requirement?

Each of the billions of cells in your body is a living machine. Even while you sleep, the metabolic activities of growth, respiration, repair and replacement go on. These processes require energy. Nutritionists such as Elson Haas, M.D., refer to the basal metabolic rate, or BMR, as the rate at which your body burns calories -- its basal caloric requirement -- in order to maintain its functions when you are at rest.

BMR Defined

According to "Taber's Cyclopedic Medical Dictionary," basal metabolic rate should be measured while you are at rest, 12 hours after a meal, in a comfortable temperature, with no emotional excitement and no exercise or activity preceding the determination. Different mathematical formulas are used to calculate BMR for men and women, but a very rough estimate of your daily BMR can be obtained by taking your weight in pounds and adding a "0" to the end. For example, if you weigh 160 lbs., you would need to consume approximately 1,600 calories each day to meet your basal caloric requirements.

Variables

Your BMR is influenced by a variety of factors, including thyroid function, gender, type and frequency of exercise, age, percentage of body fat, total body weight, genetics and ambient temperature. For example, if your thyroid function is low, your BMR drops and your basal caloric requirement falls. Heavier people have a higher BMR because it takes more calories to maintain a higher body weight. In general, older people have a lower BMR than younger people. According to a study published in the March 2011 issue of "Medicine and Science in Sports and Exercise," your BMR -- as measured by skeletal muscle oxidative capacity -- increases with regular exercise.

Diet-Induced Thermogenesis

The process of digesting food requires energy. The breakdown of fats, carbohydrates and proteins into their constituent parts, the absorption of nutrients through the intestinal wall and the processing and storage of those nutrients all come at a caloric cost. This additional energy expenditure, called diet-induced thermogenesis, or DIT, is a small part -- typically around 10 percent -- of your total daily energy expenditure, according to a 2004 review in "Nutrition and Metabolism." DIT should not be included in your BMR calculations.

Considerations

Basal metabolic rate, diet-induced thermogenesis and the caloric cost of physical activity are the three components of total daily energy expenditure. BMR determines the number of calories you burn while you are at rest, but it does not include the calories needed for digestion and assimilation of your food. BMR can be increased to a certain extent by regular exercise, which enhances skeletal muscle oxidation and accelerates caloric expenditure even during periods of rest.