It's well established that regular exercise benefits our bodies, not least in protecting against obesity, but scientists are continuing to look more closely at why this happens on a molecular level.
In a new study, scientists put mice on intense treadmill workouts and analyzed how the chemicals in the cells of the animals then began to change over time. They found the appearance of a metabolite called Lac-Phe (N-lactoyl-phenylalanine), synthesized from lactate and phenylalanine.
Phenylalanine is an amino acid that combines to make proteins, and you might be familiar with lactate: It is produced by the body after strenuous exercise.
The study authors think they've found an important biological pathway opened up by exercise, which then has an impact on the rest of the body – specifically in the level of appetite and the amount of food taken in.
Further tests confirmed these results. Researchers gave high doses of Lac-Phe to mice on a high-fat diet, resulting in the mice eating about half as much over the next 12 hours compared to a group of control mice. Meanwhile, the movement and energy expenditure of the animals remained unchanged.
Over a period of 10 days, the Lac-Phe doses led to a drop in food intake, a resulting drop in body weight, and improved glucose tolerance in the mice. Those are positive results when thinking about ways to combat obesity and obesity-related disease.
There were some caveats, though. The differences in appetite suppression caused by Lac-Phe were only noticeable after exercise and in mice on a high-fat diet. The same effects weren't seen in more sedentary mice fed normally.
The scientists also looked at the effects of exercise in humans and racehorses, finding elevated levels of Lac-Phe here, too, most notably after sprinting in people. However, the knock-on effects weren't looked into, and more research will be needed to see if these results translate fully into human beings.
By shedding more light on the molecular responses to physical activity, the findings of the study will help in a number of areas of research, including treatments.
There's likely a lot more to discover. The researchers note that as Lac-Phe is produced in multiple cell types in mice, it's likely that it's not just the muscles in the body that know when we're working out.
"Future work uncovering the downstream molecular and cellular mediators of Lac-Phe action in the brain may provide new therapeutic opportunities to capture the cardiometabolic benefits of physical activity for human health," write the researchers.
The research has been published in Nature.