Do adaptive changes in metabolic rate favor weight regain in weight-reduced individuals? An examination of the set-point theory. Weinsier RL, Nagy TR, Hunter GR, Darnell BE, Hensrud DD, Weiss HL. Am J Clin Nutr. 2000 Nov;72(5):1088-94. [FREE FULL TEXT]

From the study:

Abstract
BACKGROUND:
Obese persons generally regain lost weight, suggesting that adaptive metabolic changes favor return to a preset weight.

OBJECTIVE:
Our objective was to determine whether adaptive changes in resting metabolic rate (RMR) and thyroid hormones occur in weight-reduced persons, predisposing them to long-term weight gain.

DESIGN:
Twenty-four overweight, postmenopausal women were studied at a clinical research center in four 10-d study phases: the overweight state (phase 1, energy balance; phase 2, 3350 kJ/d) and after reduction to a normal-weight state (phase 3, 3350 kJ/d; phase 4, energy balance). Weight-reduced women were matched with 24 never-overweight control subjects. After each study phase, assessments included RMR (by indirect calorimetry), body composition (by hydrostatic weighing), serum triiodothyronine (T(3)), and reverse T(3) (rT(3)). Body weight was measured 4 y later, without intervention.

RESULTS:
Body composition-adjusted RMR and T(3):rT(3) fell during acute (phase 2) and chronic (phase 3) energy restriction (P: < 0.01), but returned to baseline in the normal-weight, energy-balanced state (phase 4; mean weight loss: 12.9 +/- 2.0 kg). RMR among weight-reduced women (4771 +/- 414 kJ/d) was not significantly different from that in control subjects (4955 +/- 414 kJ/d; P: = 0.14), and lower RMR did not predict greater 4-y weight regain (r = 0.27, NS).

CONCLUSIONS:
Energy restriction produces a transient hypothyroid-hypometabolic state that normalizes on return to energy-balanced conditions. Failure to establish energy balance after weight loss gives the misleading impression that weight-reduced persons are energy conservative and predisposed to weight regain. Our findings do not provide evidence in support of adaptive metabolic changes as an explanation for the tendency of weight-reduced persons to regain weight.

My comments:

This study is interesting for a number of reasons. First, the main finding was that putting overweight women on an 800 calorie per day diet did rapidly result in weight loss averaging 28 lb in an average of 15.4 weeks (12-20). That’s 1.82 pounds per week, so not bad at all. The diet did however decrease their thyroid hormone and did result in the resting metabolic rate of the dieters being decreased 6%. That sucks, however, once the weight was lost and the dieters were put on an isocaloric diet, both thyroid hormone and metabolism returned to a “weight adjusted” normal (by my math almost normal at least) and it took only 10 days for it to happen. It’s worth pointing out that “weight adjusted” means that as you lose weight, both the lean tissue and the fat lost results in a lesser metabolic rate. This means that skinny people burn fewer calories doing nothing than do fatter people. What they found however, was that after losing weight and establishing a maintenance diet, the formerly overweight subjects’ metabolisms were nearly the same as women their size should be, and based on metabolism they were not physically predisposed to gain their weight back. So that’s good news, and it means dieting works and you weren’t physically set up to fail afterwards.  At least that’s the statistical significant answer. Absolute numbers there was a 44 calorie daily difference in adjusted metabolic rate, which may not have been statistically significant and isn’t dooming, but certainly doesn’t help. If not normalized in time, doing the math 44 calories x 365 days / 3500 calories per pound of fat works out to gaining 4.6 pounds per year or 18.35 pounds over the 4 year follow up. That might not be enough to explain all the actual (24.4 lb) gain in the following 4 years, but it sure explains a lot of it. They said the “weight-gain tendency of obesity-prone persons appears to be caused by factors other than variations in metabolic rate” but I don’t know, a larger sample with the same findings probably would have been statistically significant. So to me the findings and the conclusions are a bit questionable.

Which brings me to thinking about intermittent fasting (IF). The results of this study got me wondering about the results of short term but full-on fasting for four days.  With 4 days of fasting, metabolic rate increased over 10%. Such that I’d like to know and how this would relate to IF where short term fasts are continued regularly. I would also like to know what happens to thyroid levels and metabolic rate when intermittent fasting is and isn’t combined with caloric restriction. Caloric restriction generally (but not always) happens without trying when doing intermittent fasting. I would expect, or at least hope, the metabolic rate increase from fasting might help offset the short term metabolic slowdown from caloric restriction. Other research found less lean tissue loss with IF as compared to typical caloric restriction diets, which if true would have preserve a higher metabolic rate.

Finally, I don’t think of IF as a weight loss diet. I don’t use it as such. Rather it’s a very simple healthy eating plan, that saves time and money and  lets you eat large meals of most anything you want. It just has the frequent side effects of fat loss, improved willpower, and breaking the connection/addiction to sugary/fatty foods which gradually makes you “want” to eat healthier. Such that it’s not something you go into with the idea of going off later on. Hence, I would expect the weight lost with IF to be lasting, so it will be interesting to see how this all plays out in the research going forward.