All human activities require energy in the form of kilocalories. Basal metabolic rate (BMR) is the term used to describe the energy required to lie at rest for 24 hours while breathing and maintaining cellular metabolism. Additional energy is required to digest food and is referred to as the thermo effect of food (TEF). Most individuals in non-physical occupations would require approximately 130% x BMR to support the normal activity of daily living. Vigorous exercise activities or work would require more kilocalories (AEE or Activity Energy Expenditure). The sum of all these would be called total energy expenditure (TEE). Energy requirements are influenced by age, heredity, sex, body composition, ambient temperature, body size and the type, duration, intensity and frequency of exercise. Certain medications may increase or decrease energy expenditure. A simple method of calculation is presented below:

Estimated Daily Kilocalorie Requirements for Adults (kcal)
Activity Level	Men	Women
Light	30	30
Moderate	40	37
Heavy	50	44

1. National Research Research Council. Recommended Dietary Allowances, 10th ed. Washington, Conational Academy Press; 1989.

	BMR be calculated using the Harris Benedict Equation:
	Female . . . .	655 + 9.6 (wt in kg) + 1.8 (ht in cm) – 4.7 (age)
	Male  . . . . .	67 + 14 (kg) + 5 (cm) – 6.7 (age)
	BMR may also be determined more accurately by performing indirect calorimetry. Traditionally, this technology was cumbersome and required expensive equipment. Recently, a relatively inexpensive handheld device (BodyGem®) has become available that performs the calculation with greater accessibility and ease. The study takes about 15 minutes and is best performed in a fasted state. At left, a patient is using a BodyGem® device.

So, let’s apply the information on body composition and energy expenditure to real life examples.

Maura Height 5 '7.5" Weight (lb) 133 BMI (kg/ht m2) 20.7 Age 46 Fat % 22.9 Body Cell Mass (BCM) in (lb) 57.9 Total body water (liters) 34.6 Measured REE (kcal) by indirect calorimetry 1520 Predicted REE by Harris-Benedict equation 1327 Additional kcal needed for activities of daily living 608 Average daily exercise expenditure (kcal) 428 Total daily kcal expenditure 2556

Terry Height 5'3" Weight (lb) 270 BMI (kg/ht m2) 47.9 Age 44 Fat % 53.6 Body Cell Mass (BCM) in (lb) 86.3 Total body water (liters) 44.5 Measured REE (kcal) by indirect calorimetry 1820 Predicted REE by Harris-Benedict equation 1914 Additional kcal needed for activities of daily living 364 Average daily exercise expenditure (kcal) 214 Total daily kcal expenditure 2398

Above are body composition data from two subjects. Both are female and similar in age. Maura's BMI would be in the normal range while Terry's is considered morbidly obese by NIH criteria. The body fat percentage, as measured by BIA, is normal for Maura and obese for Terry. Although Terry weighs twice Maura's weight, she burns a mere 300 extra kilocalories at rest.

The subjects report their average activity patterns. Maura, a self-described "Type A", enjoys lots of physical activity. Her job requires lots of walking between four buildings in a major hospital. She always takes the stairs in the buildings and in the parking garage. Her fitness routine includes distance running (20 miles total per week; 8-9 minute/mile pace), 2 resistance training sessions per week, and 2 one-hour yoga workouts.

Terry describes herself as "laid-back". Her administrative job consists of sitting at a desk all day. She always takes the elevators between floors and has little need to walk at work. Her exercise routine consists of walking 2 miles twice weekly (20 minute/mile pace), 30 minutes on the Life Cycle with low resistance, and two 20 minute weight sessions with machines. She acknowledges that her body weight limits her activity in general ,and her comfort during exercise. She is easily distracted from her workout routine and often goes for weeks with no activity.

• Obese individuals do not require proportionately more kcal than slender individuals.
• Although increased body weight is associated with greater energy expenditure when exercising, the excess weight usually limits the type, duration and intensity of exercise.
• Having a relatively high percentage of body weight in the form of muscle mass is advantageous since muscle burns three times the amount of kilocalories as fat tissue in the rested state.
• An overall active lifestyle is likely to increase resting energy expenditure.
• Simple lifestyle choices such as increasing walking and stair climbing during the day can make significant differences in energy expenditure and body weight.

 

Content questions should be directed to: Marilyn.S.Edwards, Ph.D., R.D.
or Maggie McQuiggan, M.S.
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