Physiology · Temperature, exercise and metabolism
Energy balance, food intake and obesity !
- Regulation
- Exam priority: medium
Weight changes when what we eat differs from what we burn; the hypothalamus tries to keep that balance with hunger and fullness signals.
Updated 2026-11-01
Also called: Leptin and ghrelin, Appetite control
See it in 3D: Hypothalamus · Stomach
What it is
The arcuate nucleus of the hypothalamus integrates long-term signals (leptin and insulin, which report how much fat there is) and short-term ones (ghrelin, gastric stretch, CCK, GLP-1, PYY). Two opposing neuron groups, POMC/CART and NPY/AgRP, choose between fullness and hunger through the MC4R receptor. Obesity arises when this system defends a high weight in a setting of plentiful food and little activity.
Regulation
- −Leptin (fat cell): Activates POMC/CART and inhibits NPY/AgRP in the arcuate nucleus: less hunger, more expenditure.
- −Insulin: Fullness signal in the hypothalamus, parallel to leptin.
- −CCK, GLP-1, PYY (gut): Short-term fullness; GLP-1 also slows gastric emptying.
- −Gastric stretch (vagus): Mechanical fullness signal to the brainstem.
- +Ghrelin (stomach): Activates NPY/AgRP: hunger before meals.
- +Falling leptin in fasting: Raises hunger and lowers expenditure and the thyroid and gonadal axes.
Clinical notes
- After weight loss leptin falls and energy expenditure drops more than expected: this is why keeping weight off is hard.
- Visceral obesity delivers fatty acids and cytokines to the liver: insulin resistance, fatty liver and metabolic syndrome.
- Ventromedial hypothalamic damage (tumours, surgery): hyperphagia and obesity.
- In Colombia obesity has grown across all socioeconomic levels, alongside undernutrition in some regions (double burden).
Test yourself
Think of the answer, then tap the question to see it.
Why doesn't giving leptin usually reduce weight in common obesity?
Leptin is already high from abundant fat; there is hypothalamic leptin resistance. Only people with congenital leptin deficiency respond.
What happens to appetite if the ventromedial hypothalamus is damaged?
The fullness signal is lost, causing hyperphagia and obesity.
Why is visceral fat more linked to insulin resistance than subcutaneous fat?
It drains into the portal vein, delivering free fatty acids and cytokines straight to the liver, which raises gluconeogenesis and VLDL output.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Energy metabolism and basal metabolic rate
- Fed and fasting states: the hormonal switch
- Prolonged fasting and starvation
Related conditions
In Biochemistry
In Pharmacology
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 24.7 Nutrition and Diet (OpenStax (Rice University), 2022); Obesity: MedlinePlus (MedlinePlus, US National Library of Medicine, 2026); Epidemiologic and Etiologic Considerations of Obesity (StatPearls (NCBI Bookshelf), 2025); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 72). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.