Response to “Overstated metabolic adaptation after ‘The Biggest Loser’ intervention”

Abstract

Kuchnia et al. claim that metabolic adaptation was overstated because stress, anxiety, and weight gain artificially elevated the baseline resting metabolic rate (RMR) measurements. However, baseline RMR was not significantly different from standard prediction equations 1, and subjects were weight stable in the 17 days before the measurements (−31 ± 86 g/d; P = 0.72). Furthermore, anxiety increases RMR by only ∼100 kcal/day (2), which is far too small to explain our observations. While mean RMR was ∼350 kcal/day lower in a retrospectively pair matched group of bariatric surgery patients (3), this may have been due to lack of randomization and greater insulin resistance in the surgery patients who may have followed common advice to decrease food intake and lose weight before the surgery, thereby suppressing RMR. The mean metabolic adaptation calculated using this equation is mathematically identical to the value we reported and therefore invalidates the claim that the high y-intercept could negate our results. Equation 1 above also illustrates that to explain the observed metabolic adaptation, the mean FFM measurements would have to be 13 kg and 24 kg lower than reported at the end of the competition and after 6 years, respectively. Such large systematic DXA errors suggested by Kuchnia et al. are frankly implausible and would indicate a profound loss of FFM. Kuchnia et al. noted in passing that we used a slightly different RMR prediction equation 1 compared with a previous report (5). This was because we employed a common indirect calorimetry equation to minimize the potential bias of using different equations to calculate RMR between the carts. Our extensive testing revealed no significant systematic bias in gas exchange measurements between instruments, which would need to be ≥17% or ≥440 kcal/day to render our observations statistically insignificant (1). Finally, the reported physical activity energy expenditure after 6 years was not significantly different from when participants had returned home from the ranch before the end of “The Biggest Loser” competition (1) but was considerably less than on the ranch while engaging in >3 h/day of vigorous exercise (6). We previously concluded that the “Biggest Loser” exercise regimen in combination with the ∼50% caloric restriction was unsustainable (6)—a conclusion now strengthened by the increased calorie intake and weight gain observed 6 years later (1).