Termogenesis

Termogenesis, a less common term for thermogenesis, denotes the production of heat in living organisms as part of energy expenditure. In mammals, thermogenesis occurs through multiple pathways. Basal thermogenesis is the heat produced at rest as a component of normal metabolism, while adaptive thermogenesis increases heat production in response to environmental or dietary stimuli. Shivering thermogenesis uses rapid, voluntary or reflexive muscle contractions to generate heat. Nonshivering thermogenesis relies primarily on brown adipose tissue, which contains mitochondria rich in the protein UCP1. UCP1 uncouples oxidative phosphorylation from ATP production, releasing energy as heat. Beige or brite adipocytes can emerge in white adipose tissue under certain stimuli and contribute to nonshivering thermogenesis.

The sympathetic nervous system, via norepinephrine, activates UCP1 and elevates thermogenesis. Thyroid hormones also modulate metabolic rate and heat production, interacting with catecholaminergic pathways. Diet-induced thermogenesis refers to the energy cost of processing, absorbing, and storing nutrients, particularly proteins.

In humans, brown adipose tissue is most prominent in infants and persists in small amounts in some adults, contributing to thermoregulation and energy balance. Across species, thermogenesis supports temperature homeostasis, survival in cold environments, and energy management. Measurements of thermogenesis commonly use indirect calorimetry to estimate energy expenditure and, in some cases, infrared thermography to assess heat production.

Clinical and research relevance centers on obesity and metabolic disorders, where strategies to enhance thermogenesis or brown fat activity are explored to increase energy expenditure. Conversely, dysregulated thermogenesis can affect heat tolerance and metabolic health in various disease states.