Leptin
The fat-tissue hormone that tells the brain how much energy is stored — and whose falling levels drive post-diet hunger.
Leptin is produced by fat cells in proportion to their size: more stored energy, more leptin, and the hypothalamus reads that level as the body's fuel gauge. When dieting shrinks fat stores, leptin drops sharply — and the brain responds exactly as designed, raising hunger, sharpening food attention, and trimming energy expenditure.
That response is the biology behind rebound weight gain and the "set point" experience, and it explains a common misunderstanding: obesity usually involves leptin resistance (high levels, blunted response), so taking extra leptin doesn't help. GLP-1 medications earn part of their keep here, counteracting the hunger surge that falling leptin produces — pharmacology leaning against physiology.
This glossary entry is general information, not medical advice, and is written to be consistent with FDA prescribing information and primary trial publications as of its last review. Always consult a licensed healthcare provider for personal medical decisions.
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