Imagine that your resting energy expenditure (REE) declined by hundreds of calories per day after losing weight. Maintaining your new lower weight requires the equivalent of eating 1 less meal/d or adding a substantial amount of physical activity. While it would be profoundly unfair if your REE was now significantly lower than someone of the same sex, age, and size who had never needed to lose weight, such a comparison does not alter the fact that it is the decrease in REE that translates to the permanent behavior change required to keep the weight off.
A new cross-sectional study by Ostendorf et al. (1) compared REE between 3 groups: people with obesity, people who maintained substantial weight loss, and normal-weight controls who never had obesity. People who successfully maintained weight loss had no statistically significant REE differences compared with the other groups after adjustment for fat-free mass (FFM), fat mass (FM), age, and sex. In other words, REE in successful weight loss maintainers was not disproportionately lower than expected compared with those who were not maintaining a substantial amount of lost weight. (Both control groups weighed an average of ∼6% less than their reported maximum adult weight compared with ∼27% less in the weight-loss maintainers.) Nevertheless, maintaining substantial weight loss over the long term is not easy (2).
Because Ostendorfer et al. (1) used a cross-sectional design, it is unknown how REE changed in their subjects who successfully maintained lost weight. The weight loss maintainers had an average maximum weight similar to the control subjects with obesity, so they likely started with a similar REEs and therefore experienced an average decrease in REE of ∼200 kcal/d—the equivalent of a small meal or ∼30 min of moderate-intensity exercise every day.
Longitudinal studies have suggested that decreases in REE after weight loss are greater than expected based on changes in body composition and age, and such metabolic adaptations persist for years (3–5). Ostendorfer et al. contrasted their results with our recent longitudinal study of “The Biggest Loser” contestants (6), who experienced large decreases in REE after losing an average of ∼60 kg during a 30-wk weight loss competition and maintained their REE at this lower value 6 y later despite regaining about two-thirds of the weight lost. After adjusting the REE data for the measured changes in body composition and age using regression equations derived from “The Biggest Loser” contestants’ baseline data, the observed decreases in REE were substantially lower than expected at the end of the 30-wk competition and still lower 6 y later.
Interestingly, Ostendorfer et al. showed that the baseline REE equation from “The Biggest Loser” did not accurately predict REE in their cohorts. “The Biggest Loser” equation was not intended to be applied to other cohorts because the contestants’ average starting weight, BMI, and degree of weight loss exceeded even the most extreme individual studied by Ostendorfer et al. Nevertheless, the poor performance of “The Biggest Loser” REE equation raises the question of whether the observed REE changes could have been better predicted using different equations. Perhaps life was fair to “The Biggest Loser” contestants after all?
The regression equations of Ostendorfer et al. (1) varied depending on the cohort, but as an indication of their validity the FFM and FM coefficients should be similar to those calculated using a physiologically based model that accounts for how different organs varying in size and metabolic rate are related to FFM (19 kcal · kg–1 · d–1) and FM (4.5 kcal · kg–1 · d–1) (7). The 3 equations proposed by Ostendorfer et al. had FFM coefficients of βFFM = 19.4, 15.0, and 16.9 kcal · kg–1 · d–1 and FM coefficients of βFM = 1.4, 9.4, and 7.6 kcal · kg–1 · d–1 in control subjects without obesity, control subjects with obesity, and all control subjects, respectively. Age typically reduces REE by <10 kcal · d−1 · y−1, and the coefficients in Ostendorfer et al. ranged from βage = −2.4 to −5.8 kcal · d−1 · y−1. For comparison, the REE equation derived from baseline “The Biggest Loser” data had coefficients of βFFM = 21.2 kcal · kg–1 · d–1, βFM = 1.4 kcal · kg–1 · d–1, and βage = −7.1 kcal · d−1 · y−1.
Predicted REE changes after weight loss or gain can be calculated using the regression equations as follows:
 |
(1) |
Applied to “The Biggest Loser” data, the equations of Ostendorfer et al. resulted in predicted mean REE changes that ranged from −283 to −613 kcal/d at the end of the 30-wk competition (the measured REE change was −611 kcal/d) and from −134 to −227 kcal/d after 6 y (the measured REE change was −704 kcal/d). In other words, the observed REE changes in “The Biggest Loser” contestants could not be explained by the Ostendorfer et al. equations. Only the equation with the very large FM coefficient βFM = 9.4 kcal · kg–1 · d–1 (double the expected value of 4.5 kcal · kg–1 · d–1 based on the specific metabolic rate of adipose tissue) could explain the 30-wk REE changes resulting primarily from the 47.2 kg average loss of FM. The REE values 6 y later were unexplained by any equation. Indeed, the persistent metabolic adaptation in “The Biggest Loser” contestants remains somewhat mysterious. The decline in REE experienced by “The Biggest Loser” contestants may have been a unique response to the extreme weight loss intervention. Alternatively, their high levels of physical activity (8) may have resulted in depressed REE, as predicted by the controversial Constrained Energy Expenditure Model (9).
Successful weight loss maintainers are relatively uncommon (10) and the lack of metabolic adaptation in this special population might have been the reason why they kept off their lost weight in the first place. In other words, had they experienced a greater reduction in REE after weight loss, then avoidance of weight regain would have required greater reductions in calorie intake or increases in physical activity to compensate for their relatively depressed REE. Adherence to these larger behavior changes would be more difficult, thereby resulting in a greater propensity for weight regain. Such individuals would therefore have been less likely to be in the group of successful weight loss maintainers studied by Ostendorfer et al. (1).
While it makes sense that individuals experiencing the greatest reductions in REE might have the most difficulty keeping the weight off, is there any evidence to support this hypothesis? Perhaps the opposite. Individual weight regain 6 y after “The Biggest Loser” competition was unrelated to the degree of metabolic adaptation at the end of the competition. Indeed, those who kept off the most weight had the greatest ongoing metabolic adaptation at 6 y (6) and had the greatest increase in physical activity (8). Similarly, Ostendorfer et al. found that the weight loss maintainers who had lost the most weight also had relatively lower REE than predicted by their regression equations. These data suggest that the metabolic adaptations that decrease REE occurred in response to the behavior changes that caused weight loss and its maintenance. Behavior is in the driver's seat and REE is along for the ride.
ACKNOWLEDGEMENTS
KDH is currently collaborating with several co-authors of the original article by Ostendorfer et al. on an unrelated topic.
Notes
Supported by the Intramural Research Program of the NIH, National Institute of Diabetes & Digestive & Kidney Diseases.
Abbreviations used:
- FFM
fat-free mass
- FM
fat mass
- REE
resting energy expenditure
REFERENCES
- 1. Ostendorf DM, Melanson EL, Caldwell AE, Creasy SA, Pan Z, MacLean PS, Wyatt HR, Hill JO, Catenacci VA. No consistent evidence of a disproportionately low resting energy expenditure in long-term successful weight-loss maintainers. Am J Clin Nutr. 2018;108:658–66. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2. Hall KD, Kahan S. Maintenance of lost weight and long-term management of obesity. Med Clin North Am. 2018;102(1):183–97. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3. Rosenbaum M, Hirsch J, Gallagher DA, Leibel RL. Long-term persistence of adaptive thermogenesis in subjects who have maintained a reduced body weight. Am J Clin Nutr. 2008;88(4):906–12. [DOI] [PubMed] [Google Scholar]
- 4. Rosenbaum M, Leibel RL. Adaptive thermogenesis in humans. Int J Obes (Lond). 2010;34 Suppl 1:S47–55. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5. Westerterp KR. Metabolic adaptations to over- and underfeeding—still a matter of debate?. Eur J Clin Nutr. 2013;67(5):443–5. [DOI] [PubMed] [Google Scholar]
- 6. Fothergill E, Guo J, Howard L, Kerns JC, Knuth ND, Brychta R, Chen KY, Skarulis MC, Walter M, Walter PJ et al. Persistent metabolic adaptation 6 years after “The Biggest Loser” competition. Obesity (Silver Spring). 2016;24(8):1612–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7. Hall KD. Predicting metabolic adaptation, body weight change, and energy intake in humans. Am J Physiol Endocrinol Metab. 2010;298(3):E449–66. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8. Kerns JC, Guo J, Fothergill E, Howard L, Knuth ND, Brychta R, Chen KY, Skarulis MC, Walter PJ, Hall KD. Increased physical activity associated with less weight regain six years after “The Biggest Loser” competition. Obesity (Silver Spring). 2017;25(11):1838–43. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9. Pontzer H. Constrained total energy expenditure and the evolutionary biology of energy balance. Exerc Sport Sci Rev. 2015;43(3):110–6. [DOI] [PubMed] [Google Scholar]
- 10. Wing RR, Phelan S. Long-term weight loss maintenance. Am J Clin Nutr. 2005;82(1 Suppl):222S–5S. [DOI] [PubMed] [Google Scholar]