Metabolic adaptation to caloric restriction and subsequent refeeding: the Minnesota Starvation Experiment revisited.
Level 2 - randomized trial
Individual controlled sequential dietary intervention trial
PubMed 26399868 · doi:10.3945/ajcn.115.109173
What was done
Thirty-two nonobese men underwent a sequential dietary protocol consisting of 1 week of overfeeding (+50% of energy requirements), 3 weeks of severe caloric restriction (-50% of energy requirements), and 2 weeks of refeeding (+50% of energy requirements). Researchers evaluated adaptive thermogenesis (fat-free mass-independent reduction in resting energy expenditure) and its endocrine/physiological correlates using quantitative magnetic resonance, whole-body MRI, isotope dilution, and nitrogen and fluid balances.
What was found
Body weight shifted by +1.8 kg during overfeeding, -6.0 kg during caloric restriction, and +3.5 kg during refeeding. Caloric restriction decreased fat mass by 114 g/day and fat-free mass (FFM) by 159 g/day, with organ-specific decreases in skeletal muscle (-5%), liver (-13%), and kidneys (-8%). Caloric restriction lowered resting energy expenditure (REE) by 266 kcal/day, respiratory quotient by 15%, heart rate by 14%, blood pressure by 7%, creatinine clearance by 12%, walking energy cost by 22%, sympathetic nervous system activity by 38%, leptin by 44%, insulin by 54%, adiponectin by 49%, tri-iodothyronine (T3) by 39%, and testosterone by 11%. Adaptive thermogenesis was 108 kcal/day (48% of the REE reduction); 36 kcal/day was explained by changes in FFM organ composition, leaving 72 kcal/day as true adaptive thermogenesis. Adaptive thermogenesis became significant within ≤3 days of restriction and correlated with decreases in insulin secretion (r = 0.92, P < 0.001), heart rate (r = 0.60, P < 0.05), creatinine clearance (r = 0.79, P < 0.05), negative fluid balance (r = 0.51, P < 0.01), and free water clearance rate (r = -0.90, P < 0.002). Sympathetic activity, leptin, ghrelin, and T3 were not significantly related to adaptive thermogenesis.
Why it matters
This study demonstrates that adaptive thermogenesis occurs within days of caloric restriction and is driven by rapid drops in insulin secretion and fluid balance dynamics rather than classical sustained changes in leptin or thyroid hormone concentrations.
Limits
The study was conducted in a small sample of 32 nonobese men, limiting generalizability to women and individuals with overweight or obesity. The sequential design lacked a parallel, non-restricted control group, and the abstract does not report long-term maintenance outcomes beyond the 2-week refeeding phase.
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