Adaptive Metabolic Rate Changes Not Responsible For Weight Regain in Dieters
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WESTPORT, CT (Reuters Health) Nov 8 - Resting metabolic rate, which declines during periods of energy restriction, returns to pre-weight loss values once energy balance is restored, according to results of a recent clinical trial. These findings do not support the set-point theory of metabolic regulation as the reason for the tendency of obesity-prone persons to regain weight following weight reduction.

Dr. Roland L. Weinsier, of the University of Alabama at Birmingham, and associates studied 24 overweight women with body mass index (BMI) between 25 kg/meter squared and 30 kg/meter squared and with a family history of overweight, as well as 24 never-overweight control subjects. The investigators describe their findings in the November issue of the American Journal of Clinical Nutrition.

The investigators measured the subjects' resting metabolic rate and the ratio of serum triiodothyronine (T3) to reverse triiodothyronine (rT3) during the period of the study. The overweight women maintained an energy-restricted diet — 3350 kJ per day — until they lost at least 10 kg and reached a BMI of less than 25.

Resting metabolic rate and T3:rT3 fell within 10 days of beginning the restricted diet and remained depressed until the women resumed an energy balance diet. Ten days later, the resting metabolic rate and T3:rT3 values had returned to levels observed before going on the diet, neither value of which was significantly different from that of control subjects.

After approximately 4 years of follow-up, the overweight women regained an average of 87% of the weight they had lost while dieting. The researchers observed no trend for greater weight regain among women with a lower resting metabolic rate.

Dr. Weinsier's group writes, "If metabolic measures are obtained in weight-reduced individuals before energy balance is fully restored, results would give the misleading impression that weight-reduced persons are hypometabolic and prone to weight regain."

They further note that thyroid concentrations may be of use in documenting that patients have returned to an energy-balanced state following weight loss.

The investigators conclude that energy restriction, rather than weight reduction, is associated with a relative hypothyroid state and a reduced resting metabolic rate.

Am J Clin Nutr 2000;72:1088-1094.