Awake and fed thermogenesis (AFT) is the energy expenditure (EE) of the non-active fed condition above the minimum metabolic requirement during sleep, and is composed of the thermic effect of food and the cost of being awake. AFT was estimated from whole room 24-h EE measures in 509 healthy subjects (368 Native Americans and 141 Whites) while subjects consumed a eucaloric diet. Follow-up data was available for 290 Native Americans (median follow-up time: 6.6 years).
AFT accounted for approximately 10% of 24-h EE, and explained a significant portion of deviations from expected energy requirements. Energy intake was the major determinant of AFT. AFT, normalized as a percentage of intake, was inversely related to age, fasting glucose concentration, and showed a nonlinear relationship with waist circumference and BMI. Spline analysis demonstrated that AFT becomes inversely related to BMI at an inflection point of 29 kg/m2. The residual variance of AFT after accounting for covariates predicted future weight change only in subjects with a BMI>29 kg/m2.
AFT may influence daily energy balance, is reduced in obese individuals, and predicts future weight gain in these subjects. Once central adiposity develops, a blunting of AFT may occur that then contributes to further weight gain.
- Received May 16, 2013.
- Accepted August 16, 2013.
- © 2013 by the American Diabetes Association.
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