NEW YORK – Why are we so depressed after some workouts but not interested in eating after others?
In a new study published June 15 in the journal Nature, an international team of scientists suggests that the answer lies in part in the activity of a single molecule produced after exercise. reduce hunger. Molecules – found in the blood of rats, humans and racehorses – show up more after strenuous exercise than easy ones, suggesting that hard exercise may be the key to controlling control how much we eat afterwards.
The relationship between fitness and eating is well known to be very important. Studies have shown that people who start exercising without managing their calorie intake often lose a few pounds if at all over time and possibly gain weight.
Many factors influence that outcome, including current fitness, body mass, diet, gender, genetics, metabolic rate, and even duration of exercise. Some experiments – though not all – show that morning workouts can burn more fat than similar workouts later in the day.
So is the taste. If you feel nauseous in the hours after your workout, you could easily consume more calories than you’ve burned. But what makes us feel hungry – or not – after exercise is still a mystery. For decades, scientists have known that various substances, like the hormones leptin and ghrelin, travel to the brain and make us more or less interested in eating.
Studies show that exercise changes levels of these substances, but so do diet and sleep habits. Some researchers are beginning to wonder if there may be some specific type of exercise response that affects appetite.
So scientists from Stanford University School of Medicine, Baylor College of Medicine, the University of Copenhagen and others used newly developed techniques to look for molecules that occur in larger numbers in blood after exercise. They started with mice, placing them on small treadmills to run at increasingly high speeds until they were exhausted. They took blood first and then and then compared the levels of thousands of molecules in the rodents’ blood.
One stands out, gains more than any other molecule. It has been previously documented in a few metabolism and exercise studies, but its chemical and biological roles are still unknown. The scientists discovered that this new molecule – a mixture of lactate and the amino acid phenylalanine – is produced in response to high levels of lactate released during exercise. Scientists named it lac-phe.
The researchers speculate that lac-phe may be involved in energy balance after exercise, as the cells in the blood and elsewhere that make it are widely involved in energy acquisition and body mass. Maybe, they think, it affects appetite. To find out, they gave a form of lac-phe to obese mice, which often binge eat. But their kibble consumption has dropped by more than 30%. They seem to be less hungry when they have more lac-phe.
The researchers then went back to exercise. They bred mice that produced little if any and had them jog on a treadmill five times a week for a few weeks. After each run, the animals were fed as much high-fat food as they wanted. Typically, running helps rats prevent weight gain, even when on a high-calorie diet. But the animals were unable to produce as many lactase bubbles, ate more food and gained about 25% more weight than the control group.
It seems Lac-phe is key to how strenuous exercise helps rats avoid weight gain. Without it, that same exercise led to overeating.
Finally, the researchers examined lac-phe in other exercised organisms. They first found the substance in the blood of seahorses in much higher concentrations after a strenuous run than before. They then asked eight healthy young adults to exercise three times: Once by cycling at a leisurely pace for 90 minutes, another time lifting weights, and a third time sprinting for 30 seconds on a bike. stationary bike.
Lac-phe blood levels peak after each type of exercise, but they are highest after sprinting, followed by weight training. Gentle stretching exercises cause the least effect.
In other words, the more intense the exercise, the more lac-phe was produced, and at least in the rats, the lower the appetite.
Dr Richard Palmiter, professor of biochemistry at the University of Washington in Seattle and an expert in the neurobiology of behaviour, said: “The results are fascinating and add a new dimension to our thinking. about exercise and body weight regulation. of new research.
“We’ve always known that our current menu includes molecules that regulate appetite and food intake, such as leptin, ghrelin, etc. Braun, executive director of the Laboratory,” said Dr. Barry. Human Performance Clinical Researcher at Colorado State University at Fort Collins, who studies exercise and weight control. He was not involved in the new study.
Assuming the process works the same way in humans as it does in mice, the discovery of lac-phe would provide a useful lesson. Dr. Jonathan Z. Long, professor of pathology at Stanford University School of Medicine and lead author of the new study, said that if we want to avoid post-exercise hangovers, we may need to increase the intensity. practice.
The idea has intuitive and evolutionary implications, he added. “If you’re sprinting from a rhinoceros or some other threat, the autonomic nervous system screams at the brain to stop digestion and any other unnecessary processes.”
However, his research doesn’t tell us how lac-phe might interact with our brain cells to affect appetite or how strenuous exercise is to form. lac-phe or how long the effect of the molecule can last. Additionally, human exercisers are healthy young adults, which means we don’t know if lac-phe exists or functions in similar ways in other people.
However, if you want to feel less hungry after exercising, you may want to increase the pace. Throw in some hills on your next hike or sprint to the far corner. “The data suggest intensity is important for exercise and appetite control,” says Dr. Long.
This article originally appeared in The New York Times.