Leptin Resistance & Body-Weight Set-Point瘦素抵抗与体重设定点

Place · Level 3 · Condition

下丘脑防御一个体重设定点 · 瘦素 ↑ 中枢却不响应 = 瘦素抵抗 · 减重后大脑解读为挨饿 · 这不是意志力问题

Leptin · adipose-to-brain energy signal

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瘦素 · 脂肪向大脑发送的能量信号

Leptin was discovered in 1994 by Friedman's lab — a hormone secreted by adipose tissue, the long-term signal that fat tells the brain about energy reserves. This overturned the old view that fat was just a passive warehouse and formally established adipose as an endocrine organ.

The basic leptin circuit:

Adipocytes continuously secrete leptin in proportion to fat mass — more fat, higher blood leptinLeptin crosses the blood-brain barrier and reaches the hypothalamic arcuate nucleusPOMC neurons (satiety): activated by leptin → α-MSH ↑ → suppresses appetite + ↑ energy expenditureNPY/AgRP neurons (hunger): inhibited by leptin → reduced hunger drive
Leptin is not a postprandial fullness hormone (that job belongs to CCK / PYY / ). Leptin is the long-term fuel-gauge of energy reserves:

Fat reserves adequate → leptin high → brain permits normal metabolism + reproduction + immunityFat reserves low → leptin low → brain sounds the famine alarm: appetite ↑, resting metabolism ↓, reproductive hormones ↓, thyroid ↓
Clinical evidence:

Congenital leptin deficiency (ob gene mutation, extremely rare in children): perpetual hunger → morbid obesity → recombinant leptin injection dramatically reverses (Farooqi 1999 NEJM)This gave the field an illusion: 'leptin = weight-loss miracle' — we'll see that hope collapse next (Heymsfield 1999 RCT)
Key insight:

Leptin's evolutionary role is not 'to keep you lean' but to prevent starvation — it sounds the alarm when low; when high, it does not actively make you eat lessThis asymmetry is the root of every 'why I rebound after dieting' story that follows

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