Thermogenesis is the name of the process that generates heat in all warm-blooded animals. It allows them to maintain the constant internal temperature they need to survive. Thermogenesis also enables fats to be burned and converted into heat; thus when it’s not functioning properly, it’s sometimes blamed for causing excess weight and obesity. Lastly, thermogenesis is stimulated when the body has to defend itself against stress factors such as the cold or an infection: this is called adaptive thermogenesis.
There are three main ways heat is produced in the human body: hormonal thermoregulation, diet and physical activity.
With the hormonal pathway, everything takes place in the hypothalamus, a gland located at the base of the brain, which controls a number of physiological processes. When the body gets cold, the hypothalamus triggers a warming action, prompted by various signals:
In terms of diet, 40% of the food we ingest is used as fuel to produce heat, during digestion (1). The amount of energy expended in digestion varies. Lipids (fats) have the best ‘quality-energy’ ratio as they make the lowest demands on the body. Conversely, digesting proteins (followed by carbohydrates to a lesser extent) requires more energy and promotes greater dietary thermogenesis (2).
Last but not least, physical activity produces intense muscle movements as muscles contract and relax, which causes heat to be released.
It’s important to note that the mechanisms of thermoregulation vary according to sex and age. In women of reproductive age, for example, body temperature increases during ovulation due to the effect of progesterone, whereas there’s a natural decrease in body temperature in older people.
Finally, when the body is subjected to an overly-strict diet and rapid fat loss, there’s a natural, long-lasting reduction in thermogenesis. This is referred to as starvation mode. It’s a mechanism that encourages fats to be stored, as they’re less energy-intensive. It’s thus responsible for the rapid weight gain that can occur when an individual stops dieting (3).
This is a type of fatty tissue which is responsible for producing heat and can thus be found in hibernating mammals. It’s also present in humans, primarily new-born babies, and, to a lesser degree, in adults too, and even less so in obese individuals.
A specific protein in brown adipose tissue called UCP1 (or thermogenin) is responsible for emitting heat. This uncoupling protein encourages the release of heat to the detriment of energy production (4).
In addition, researchers have shown that excessive levels of certain amino acids (valine, leucine and isoleucine) are associated with obesity and diabetes. They also demonstrated that it is these amino acids which are used preferentially by brown adipose tissue for heat production (5). Stimulation of brown adipose tissue activity is therefore one of the most promising avenues of research for promoting weight loss.
Along with exercise, heat production can be stimulated by consuming foods and drinks with recognised thermogenic properties: chillies, and tea and coffee. These contain active principles (capsaicin and caffeine respectively) which stimulate the sympathetic nervous system, the main driver of thermogenesis (6). Ginger may also increase thermogenesis (7), and cinnamon may stimulate the ‘browning’ of adipose tissue (8).
Thermogenic supplements can also help to produce heat and thus increase average calorie expenditure. One such product is Advanced Fat Burner, an essential supplement that contains 5 natural ingredients (inulin, green coffee, Coleus forskohlii, chromium, Garcinia and Sphaeranthus indicus) able to stimulate thermogenesis.
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