Understanding Metabolism

Your body requires a certain number of calories to function. You burn these calories in three main ways:

  • To sustain bodily functions (staying warm, breathing, having your heart beat, etc). This is called Basal Metabolic Rate (BMR).
  • To perform activity (daily living, work and exercise). This is called the Thermic Effect of Exercise (TEE).
  • To extract energy and nutrients from food (digest, absorb and process chemically). This is the Thermic Effect of Food (TEF)

Other factors can influence the efficiency in which you burn calories. These factors include genetics, age, body composition, and medical and psychological conditions. Learn about these terms below.

Basal Metabolic Rate

Most of the calories you need in a day are for sustaining your bodily functions like your heart rate or breathing. The calories required for those functions is called Basal Metabolic Rate (BMR). BMR is, essentially, the number of calories you would use if you stayed in bed all day.

BMR accounts for 50 to 75 percent of your daily calorie needs. BMR varies depending on the amount of muscle a person has. Even at rest, the person with more muscle will burn more calories than the person with less muscle.

Thermic Effect of Exercise

The Thermic Effect of Exercise refers to the calories you burn when you perform physical activities including work like vacuuming or washing the car, transportation like walking or climbing stairs, and recreation, like golfing, swimming or dancing. Heat is released when you burn calories, which is why you feel hot when you exercise.

Roughly 30 percent of the calories you need in a day are used for TEE. This percentage is much lower in sedentary people than those who workout frequently. The calories you burn through activity are related to your amount of muscle. Muscles allow you to work harder, which burns more calories and, in turn, builds more muscle - a never-ending cycle. If you are trying to lose weight or maintain weight loss, increase your physical activity.

The Thermic Effect of Food

Believe it or not, the process of digesting and absorbing nutrients, breaking them down and utilizing them contributes 6 to 15 percent of the calories you burn in a day. That's about 180 calories, if you eat 1,800 calories. Foods that are higher in carbohydrates and protein require more energy to digest and metabolize than foods high in fat. Carbohydrates and protein have a high TEF.

To burn more calories, increase your muscle mass and perform more physical activity. You will increase your caloric requirements so you can lose and maintain weight more easily.


  • Hunt Sara M, Groff James L. "Energy balance and weight control." Advanced Nutrition and Metabolism. St. Paul, MN: West Publishing Company, 1995.

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