Why you don't feel hungry after exercise: a new explanation from scientists

Researchers from Baylor College of Medicine have discovered an additional mechanism: during physical activity, the body produces the compound Lac-Phe, which reduces appetite. The results of the study are reported by the publication Nature Metabolism.

The authors of the work emphasise that physical activity is traditionally considered an effective way to combat overweight and obesity-related diseases, including diabetes and cardiovascular pathologies. However, it remains not fully understood exactly what biological processes are responsible for this effect.

"We knew that exercise increases Lac-Phe levels in the blood - we've observed this in mice, humans and even racehorses. But until now, it wasn't clear exactly how this compound affects appetite," says one of the lead authors, Dr Yang He.

In previous experiments, scientists have already shown that administration of Lac-Phe reduces food intake in obese mice and promotes weight loss without adverse effects. The new study sheds light on exactly how this compound works.

It focused on two groups of neurons in the hypothalamus, the area of the brain responsible for hunger and satiety. These are AgRP neurons, which stimulate hunger, and PVH neurons, which suppress appetite. Normally, AgRP neurons "inhibit" the activity of PVH neurons. However, when exposed to Lac-Phe, the opposite happens: the activity of AgRP-neurons decreases, while PVH-neurons, on the contrary, are activated - as a result, the animals eat less.

"We found that Lac-Phe acts through potassium channels (KATP) on the surface of AgRP-neurons. When Lac-Phe activates these channels, the neurons die down. And if the channels are blocked, Lac-Phe loses its ability to suppress appetite," He explains.

The behaviour of the mice remained normal during the experiments, indicating that there were no side effects. This discovery offers hope for new obesity treatments based on natural biochemical processes.

"This is an important discovery: we see how a molecule produced by the body during exercise directly affects the area of the brain responsible for hunger," emphasises Dr Jonathan Long from Stanford University.

Although the study was conducted on mice, the authors are confident that their work may have implications for humans as well. In the future, they plan to study the behaviour of Lac-Phe in different metabolic states (for example, obesity and normal weight), as well as to find out how the compound gets into the brain and how safe it would be to use it in therapy.