To review factors contributing to variation in total daily energy expenditure and its primary components: (1) resting metabolic rate; (2) diet-induced thermogenesis; and (3) activity thermogenesis, including exercise energy expenditure and nonexercise activity. For each component, the expected magnitude of intra-individual variability is also considered. We also reviewed studies that quantified the variability in 24 h energy expenditure.
In humans, the coefficient of variation in the components of total daily energy expenditure is around 5-8% for resting metabolic rate, 1-2% for exercise energy expenditure, and around 20% for diet-induced thermogenesis. The coefficient of variance for 24 h energy expenditure measured using a room calorimeter for resting metabolic rate is around 5-10%. Thus, these measures are all rather reproducible. Total daily energy expenditure varies several-fold in humans, not due to variation in resting metabolic rate, diet-induced thermogenesis, or exercise thermogenesis, but rather, due to variations in nonexercise activity. A variety of factors impact nonexercise activity, including occupation, environment, education, genetics, age, gender, and body composition, but little is known about the magnitude of effect.
Resting metabolic rate, diet-induced thermogenesis, exercise energy expenditure, and 24 h energy expenditure are highly reproducible. Coefficient of variation is smallest for exercise energy expenditure, followed by resting metabolic rate, 24 h energy expenditure, and diet-induced thermogenesis. There is considerable variability in total daily energy expenditure, largely due to variations in nonexercise activity. Although the factors that impact upon nonexercise activity are understood, their contribution to variation in total daily energy expenditure is unclear.
aDepartment of Medicine, Section of Endocrinology, Diabetes, and Metabolism, University of Vermont, Burlington, Vermont, bDivision of Endocrinology, Department of Internal Medicine, Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota and cCenter for Human Nutrition and the Division of Endocrinology, Metabolism and Diabetes, University of Colorado Health Sciences Center, Denver, Colorado, USA
Correspondence to Edward L. Melanson PhD, Center for Human Nutrition, Campus Box C263, University of Colorado Health Sciences Center, Denver, CO 80262, USA Tel: +1 303 315 9019; fax: +1 303 315 9976; e-mail: email@example.com