Components of Energy Expenditure
Energy is expended by the human body in the form of resting energy expenditure (60-75%), the thermic effect of food (10%), and energy expended in physical activity (the most variable).
Resting and Basal Energy Expenditure
-REE: the energy expended in the activities necessary to sustain normal body functions and homeostasis. Activities include respiration, circulation, maintenance of body temperature, and synthesis of organic compounds.
-Basal Energy Expenditure: reflects the amount of energy used over 24 hours while physically and mentally resting. One way to think about the BEE is the energy used if you were laying on a bed for 24 hours without moving.
-Basal Metabolic Rate: energy needed to sustain metabolic activities of cells, tissues, and various processes.
Factors Affecting Resting Energy Expenditure
-Body Size: larger people have higher metabolic rates than smaller people. Tall, thin people have higher metabolic rates than short, wide people.
-Body Composition: Athletes with greater muscle have 5% higher basal metabolism than non-athletes.
-Sex: women have 5-10% lower metabolic rates than men.
-Other: fevers increase metabolic rate by about 7% for each degree increase in body temperature.
Hormones and Energy Expenditure
Women, did you ever wonder why you get more or less hungry during your menstrual cycle? This happens because the metabolic rate of women fluctuates. About 1 week before ovulation, there is an average of 400 kcal/day difference in BMR. During the second half of the menstrual cycle, there is an increase in energy expenditure. The increase in energy expenditure leads to the increase in hunger.
Thermic Effect of Food (TEF)
TEF is the increase in energy expenditure associated with the consumption of food. Components of the TEF includes energy required to digest, absorb, and metabolize nutrients.
-Fun Facts: Spicy foods enhance and prolong the effect of the TEF. When ingested every 2 hours for 12 hours, coffee increases the TEF by 8-11%.
Energy Expended in Physical Activity (EEPA)
This includes the energy expended in voluntary exercises (running and weight lifting) and involuntary exercises (shivering, fidgeting, and maintaining posture).
-Fun Facts: EEPA decreases with age due to a decrease in fat free mass and an increase in fat mass. Men generally have a higher EEPA than women.
What is a Calorie?
A calorie is the amount of heat energy required to raise the temperature of 1 ml of water 15 degrees Celsius by 1 degree.
Energy Expenditure Estimations
-The EER incorporates height, weight, age, gender, and level of physical activity (PA) to determine the amount of calories you need on a daily basis.
-PA has 4 categories: sedentary (use 1.0 for equation), low active (1.12), active (1.24), and very active (1.45).
For men:
EER= 662 - 9.53 × age (years) + PA × (15.91 x weight (kg) + 539.6 x height (meters))
For women:
EER= 354 - 6.91 × age (years) + PA × (9.36 x weight (kg) + 726 x height (meters))
Example:
30 year old female, 150 lbs (68kg), low active (1.12 PA activity factor), 5'5'' (1.65m)
EER= 354 - 6.91 x 30 + 1.12 x (9.36 x 68 + 726 x 1.65)
EER= 2,201 calories
Mahan L, Escott-Stump, S. "Food, Nutrition, and Diet Therapy." Saunders. 2004.
http://www.ncbi.nlm.nih.gov/pubmed/15534426
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1784117/
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