Research

Hormonal

Adaptive thermogenesis (AT) during caloric restriction primarily manifests as a reduction in resting energy expenditure (REE) driven by glycogen depletion and insulin suppression, rather than changes in fat mass or leptin levels.

When you start a diet, your body reduces energy expenditure quickly (within 3 days) to conserve energy. This is driven by dropping insulin and emptying glycogen stores, not by losing fat. This is a normal physiological response (adaptive thermogenesis) that makes early weight loss harder than expected, but it does not mean your metabolism is permanently damaged.

GoodQualifiesHIGH confidence
During phase 1, decreases in FFM exceed the decrease in fat mass; they are due to losses in intracellular (due to glycogen and protein mobilisation) and extracellular water (due to an increase in natriuresis) rather than to losses in cell mass per se... During phase 1, AT is explained by 'threshold model' related to the fall in insulin secretion.
Manfred J. Müller et al. · Current Obesity Reports · 2016

Why this rating

Based on controlled clinical studies (e.g., Minnesota Starvation Experiment, controlled underfeeding) with consistent findings on insulin/glycogen dynamics.

Source

Changes in Energy Expenditure with Weight Gain and Weight Loss in Humans

Manfred J. Müller et al. · Current Obesity Reports · 2016

DOI 10.1007/s13679-016-0237-4

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DOI resolved against Crossref · corpus check 2026-06-10

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