How Many Calories Should You Eat Per Day?

Many people find maintaining a healthy weight to be a challenge. One way to control weight is to know how many calories to eat in a day. Baylor College of Medicine says knowing daily calorie needs is the first step toward a healthy diet and activity plan. Estimating calorie needs takes into account resting energy expenditure, activity level and thermic effect of food.

Metabolic Rate

The metabolic rate is the rate at which an individual burns calories to sustain basic bodily functions such as respiration, circulation and body temperature. The nervous system, comprised of the brain, spinal cord and nerves, makes up half of the metabolic rate, says "Krause's Food, Nutrition and Diet Therapy." The metabolic rate varies and can be affected by periods of growth, individual body size and lean body mass.

Resting Energy Expenditure

Resting energy expenditure (REE) can be estimated using standard equations, says "Krause's." The Harris-Benedict formula has been used to estimate REE since 1919. The Harris-Benedict formula for women, 655 + 9.56 W + 1.85 H -- 4.68 A, and men, 66.5 + 13.75 W + 5.0 H -- 6.78 A, where W = weight in kilograms, H = height in centimeters and A = age in years.

Thermic Effect of Food

The thermic effect of food is the increase in the metabolic rate after eating a meal. The increase in the metabolic rate is due to the act of digestion, absorption and metabolizing of nutrients, says "Krause's." Consumption of carbohydrates and fat increases the metabolism by about 5 percent, while the consumption of protein can increase the metabolism by as much as 25 percent, the authors of "Krause's" explain. An additional 10 percent of calories can be added to the REE to cover the thermic effect of food metabolism, "Krause's" suggests.

Activity Level

Physical activity accounts for 20 percent to 50 percent of daily calorie needs, according to Baylor College of Medicine. Calories needed for physical activity depend on the type of activity, body size and fitness level. Multiply the REE by the activity factor to determine calorie needs. The very light activity factor is 1.5 and includes seated and standing activities, driving, and typing. The light activity factor is 2.5 and includes walking on a level surface at 2.5 miles per hour, carpentry, house cleaning, and table tennis. The moderate activity factor is 5.0 and includes walking at 3.5 miles per hour, weeding and cycling. The heavy activity factor is 7.0 and includes walking with a load uphill, heavy manual digging, basketball and football.

Considerations

Calorie calculations are estimates. The MyPyramid.gov website says individual calorie needs may be different from estimates. They suggest people carefully monitor their weight and adjust calorie intake to meet their weight goals.