It is well known that exercise can reduce appetite. As exercise increases the body temperature, researchers looked at whether small increases in body temperature also reduces appetite.
Appetite is controlled by a small area in the brain, called the hypothalamus. Although small, the hypothalamus plays a vital role in regulating important daily functions, such as circadian rhythm, body temperature, and emotions. Nerve cells in the hypothalamus that express proopiomelanocortin (POMC) also play a key role in controlling appetite.
It is well known that strenuous exercise can reduce appetite and cause us to eat less. However, it is unclear whether increases in body temperature due to exercise also reduce appetite or whether this is also regulated by the hypothalamus.
Cells in the hypothalamus respond to changes in body temperature
In a recent PLoS Biology publication, an American team demonstrated an association between body temperature and appetite through a series of experiments in mice.
First, the team confirmed that up to two-thirds of the nerve cells in the hypothalamus that express POMC also express TRPV1 thermoreceptors, which allow the body to adapt to environmental temperature changes. Past experiments showed that paired TRPV1 thermoreceptors are activated only when the body temperature exceeds 42°C, which is dangerously high.
The team realized that paired TRPV1 thermoreceptors could not be responsible for acute reductions in appetite. Rather, they found that lower temperatures (34°C-38°C), which better reflect exercise-induced body temperature increases, activated the TRPV1 thermoreceptor, but only when it was combined with either a TRPV3 or TRPV4 thermoreceptor (called TRPV1-like thermoreceptors).
Thermoreceptors are activated during exercise
The team went on to demonstrate that physical activity could, in fact, activate these TRPV1-like thermoreceptors by increasing not only body temperature but the temperature in the hypothalamus. The team found that physical activity caused the body temperature to increase quite rapidly and that this increase also extended to the hypothalamus.
When mice had run for five minutes on a treadmill, their body and hypothalamus temperatures both increased by approximately 1°C to 37°C. After 40 minutes of running on the treadmill, the temperatures in both had increased to almost 39°C.
Activated thermoreceptors reduce appetite
Mice that had exercised consumed significantly less food as early as ten minutes after completing the 40-minute treadmill task when compared to mice that had not exercised. The team found that the exercise-induced temperature increase in the hypothalamus activated the TRPV1-like thermoreceptors. When activated, the TRPV1-like thermoreceptors released a hormone that reduced the mice’s appetite.
Increased body temperature can reduce appetite
Overall, the team confirmed that small increases in body temperature, consistent with those achieved through physical exercise, can extend to the brain. This in turn activates thermoreceptors that reduce appetite. However, as this study was performed in mice, the degree of the response measured in mice may not be seen in humans. Further studies in humans are warranted.
Written by Natasha Tetlow, PhD
References:
(1) Jeong JH, et al. Activation of temperature-senstive TRPV1-like receptors in ARC POMC neurons reduces food intake. PLoS Biol. 2018. 16(4): e2004399. Available at doi: 10.1371/journal.pbio.2004399.
(2) Mandal, A. What is the hypothalamus? https://www.news-medical.net/health/What-is-the-Hypothalamus.aspx. Accessed 7 May 2018.
