18.4 Calories and Energy Balance

A calorie is a unit of energy derived from food and beverages, but how much energy does the body actually require? Resting energy expenditure—sometimes referred to as basal metabolic rate—is the amount of energy needed just to keep your body functioning at rest. The greatest contributors to resting energy expenditure are the brain, liver, heart, and kidneys. Resting energy expenditure accounts for about 60-70% of total daily energy expenditure. Another 8-15% of total daily energy expenditure comes from the thermic effect of food (von Loeffelholz & Birkenfeld, 2018) or the energy needed to process food for use and storage; different macronutrients have different thermic effects. Depending on an individual’s habits, up to 15-30% of total daily energy expenditure could come from exercise and the remaining total daily energy expenditure could come from non-exercise physical activity, which includes leisure activities, daily living activities, subconscious activities like fidgeting, and work-related physical activity. For example, individuals working in agricultural and labor-oriented occupations have high non-exercise activity energy expenditure. Non-exercise activity could account for anywhere from 15-50% of total daily energy expenditure depending on the lifestyle of the individual (Levine, 2004).

People who regularly consume more calories than they expend are in positive energy balance. People who consume fewer calories than their energy needs for activity and other normal body functions are in negative energy balance. Being in neutral energy balance means the body’s energy needs are being met based on expenditure.