Thermogenesis and Brown Fat
The tissue specialised in burning calories to produce heat — key in metabolic ageing
Definition
Thermogenesis is heat production by the body. Adaptive thermogenesis — increased energy expenditure in response to cold, feeding, or stress — is mediated mainly by brown adipose tissue (BAT, Brown Adipose Tissue), a specialised tissue rich in mitochondria and the UCP1 protein (uncoupling protein 1) that uncouples the respiratory chain, producing heat instead of ATP. Active BAT in adult humans was rediscovered in 2009 (PET-CT studies) and since then it is an active target in metabolism and longevity.
Detailed explanation
Adipose tissue types:
Classic BAT: thermogenic, rich in mitochondria, in neck, supraclavicular, paravertebral. Active by cold and catecholamines. Beige BAT (browning): beige adipocytes derived from WAT (white fat) that can acquire thermogenic phenotype after prolonged cold exposure or exercise. WAT (White fat): energy storage, low mitochondrial density.
The amount of active BAT inversely correlates with BMI, glycaemia, lipid profile, and age. Patients with active BAT (measurable by FDG PET-CT under 17-19°C cold exposure) have better metabolic health.
Interventions to activate/expand BAT:
Cold exposure: the most potent stimulus. Protocols: cold water 14-16°C for 5-15 min/day (Wim Hof, athletes), whole-body cryotherapy (-110°C/3 min), sleeping in a cool room (18-19°C), intermittent fresh air exposure. Van Marken Lichtenbelt's studies show increased BAT mass and metabolic improvement with 6 weeks of 17°C exposure 2 h/day. Exercise: secretes irisin and FGF21 that promote 'browning' of WAT. Ketones and fasting: activate adaptive thermogenesis. Thermogenic polyphenols: capsaicin, green tea EGCG, resveratrol (modest effect). β3-agonists: in clinical research (mirabegron, originally for overactive bladder).
Thermogenesis is one of the mechanisms by which longevity interventions simultaneously improve body composition and metabolic health — not just 'burning calories' but creating a more youthful metabolic phenotype with greater energy flexibility.
Scientific sources
- PubMed — Cold-activated brown adipose tissue in healthy men (van Marken Lichtenbelt, NEJM)
- PubMed — Cold acclimation recruits human brown fat and increases nonshivering thermogenesis
- PubMed — Beige adipocytes: discovery and functional significance
- PubMed — Brown adipose tissue and aging: mechanisms and clinical implications
Related terms
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