Move to eat less! Here's another reason to get into sports, if you needed one more. We already know that physical activity has many positive effects on the body, notably that it helps burn calories and thus... slimming down and losing weightA study from the University of South Florida and Baylor College of Medicine in Texas, USA, has just revealed a new superpower of physical exercise: it reduces appetite! Moving our bodies helps us burn fat and consume less of it—a win-win situation all around. But how does exercise regulate hunger? Thanks to a molecule that is good for us… and which, paradoxically, is produced by another molecule that, on the contrary, has a reputation for being harmful. This surprising discovery was published on September 16, 2025, in the journal Nature Metabolism.
Lac-Phe, a molecule produced during physical exercise
During intense physical activity, muscles require a large amount of energy very quickly. The mitochondria, which produce the majority of cellular energy by burning oxygen, are overwhelmed (because oxygen is depleted), and anaerobic glycolysis (which burns glucose without using oxygen) takes over. This metabolic pathway eventually generates lactate, another source of energy. But this lactate can also become lactic acid, which, when it accumulates, leads to muscle fatigue. However, this accumulation also has a positive effect: some of the lactate is transformed into lactoylphenylalanine (or Lac-Phe), an appetite-suppressant molecule that acts directly on the brain to decrease appetite.
Lac-Phe cuts the feeling of hunger
Researchers have shown in mice that Lac-Phe acts on neurons in the hypothalamus, a brain structure involved in several processes, including hunger. Two types of neurons participate in this process, in two distinct regions: AgRP neurons (named for the messenger molecule of the same name) which stimulate the sensation of hunger, located in the arcuate nucleus of the hypothalamus; and PVH neurons, located in the paraventricular nucleus of the hypothalamus, which, conversely, decrease appetite. When the body wants to eat, the former (AgRP) inhibit the latter (PVH), creating a sensation of hunger. But when the AgRPs are no longer activated, the PVHs can activate, suppressing this sensation. And that is precisely what the Lac-Phe molecule does: it inhibits the AgRP neurons, allowing the activation of the PVHs and thus reducing appetite.
Read alsoHunger sensation: these cells signal to your brain that you've eaten enough
The virtuous circle of physical activity…
Once produced in the muscles during physical activity, Lac-Phe enters the bloodstream and can thus reach the brain. Its target (or at least one of its targets) is a potassium channel on the surface of AgRP neurons, which regulates the activity of these neurons. Lac-Phe thus activates this switch, turning off these neurons and releasing PVH, which then signals to the brain that mealtime is over.
This molecule is crucial for regulating metabolism after physical activity, as it signals to the brain that the body doesn't need to eat, despite the calorie loss it has just experienced due to exertion. Exercise thus triggers a virtuous cycle, where calories are burned and not entirely replaced, resulting in a net loss that wouldn't be possible if, after every gym session, one were desperate to go to a fast-food restaurant.
…soon in pill form?
Not only does this discovery allow us to identify the precise mechanism by which exercise generates this virtuous cycle, but it could also open the door to potential pharmaceutical alternatives that mimic this effect. Have we finally found a way to reap the benefits of sport without making the slightest effort? It's reasonable to doubt it, given the list of "miracle" pills "which would mimic the positive effects of sport is already a long process, without unfortunately any real success... at least for the moment.
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