The complicated relation between resting energy expenditure and maintenance of lost weight.

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 weightloss 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: