The result, over time, can mean we eat less and control our weight better if we push ourselves a little more during exercise.
How exercise changes hunger hormones
Consider what happened when Tom Hazell, an associate professor of kinesiology at Wilfrid Laurier University in Waterloo, Canada, invited nine healthy, middle-aged men and women into an exercise lab. During their visits, he assigned them different exercises on different days, with the:
- Easy run for 30 minutes.
- One minute of fast, intense treadmill running followed by one minute of rest, repeated 10 times.
- 15-second, all-out bike intervals, interspersed with two minutes of rest, repeated eight times.
- Sitting quietly.
This experiment, published in April at Journal of Applied Physiologygrew out of earlier work, from more than a decade earlier, in which Hazell and his colleagues noticed that short training sessions in between motivated many of their volunteers to shed some fat on body.
That result was a surprise, because these workouts, often called high-intensity interval training or HIIT, seem too short to burn many calories. What might HIIT be doing that affects people’s body composition?
The researchers drew blood before and several times after each session, assessed how hungry the people felt and asked them to keep detailed food diaries the day before and the day of their workout.
Hazell and his colleagues then analyzed the blood of their volunteers for various substances, including hormones known to be in either the hind or the goose.
The most striking finding was that lactate levels increased in the blood vessels of the people after the interval sessions, compared to the levels after moderate running and the quiet sitting.
Lactate was once thought to be an undesirable waste product produced by our muscles during exercise. Most of us believe that lactic acid makes us sick.
But scientists now know Lactic acid is more favorable than harmful. It is an important signaling molecule that initiates many of the processes that lead to the beneficial effects from exercise. Pumping out lactate during exercise is, it turns out, mostly a good thing.
And the blood vessels of middle-aged volunteers in Hazell’s lab filled with lactate after each of their short, intense exercise sessions.
Even more importantly, the higher their lactate levels, the lower the amount of acylated ghrelin in their blood. Acylated ghrelin is one of the main hormones that increase appetite.
In fact, short, intense exercise increases people’s lactate and, in the process, lowers ghrelin.
Lactate likely partially blocks the release of acylated ghrelin from the stomach, where it normally originates, said Seth McCarthy, a graduate student in Hazell’s lab, who led the new study, although that possibility has to be ruled out. confirm.
More intensity, less food
According to the food diaries, the exercisers subsequently ate 129 fewer calories, on average, on the day of their one-minute intervals and 201 fewer calories after their repeated 15 -second intervals, compared to the no-exercise day. Moderate running has no measurable effect on food.
These differences are obviously small. They were not statistically significant, the scientists said, and could have been accounted for simply by people inaccurately recording what they ate on those days. The effects also varied from one person to the next, suggesting that changes in ghrelin were not the only factor at work.
“There are many biological signals that are thought to play a role” in appetite, “but there are many other psychological, environmental, and individual factors” as well, says David Stensel, a professor of exercise metabolism at Loughborough University in Britain, studying exercise and diet. He co-authored the scientific review on Appetite but was not involved in the lactate study.
However, if repeated over time, a difference of even a few hundred calories a day can help us avoid weight gain, other research shows.
The upshot is that if you want to maintain your appetite after exercise, you may want to speed up the pace. Instead of walking around on the flats, walk or run at a fast, challenging clip up a long hill, swing the arms, breathe. Or pedal a stationary bike at your top, full speed for a few 15-second spurts.
You don’t need a heart rate monitor or scientific exactitude (although, if you enjoy those things, aim for a heart rate greater than 80 percent of your maximum, which in broad terms would be 220 minus your age) .
Keep your expectations reasonable on the effects on your appetite. These tend to be short-lived “and require exercise to be performed daily or at least several times per week,” says Stensel.
Further research is also needed, on other possible explanations for how exercise affects appetite. In a 2017 study in Stensel’s lab, an hour of brisk walking on a treadmill resulted in an increase in other hormones besides lactate, including GLP-1, which is also famously involved in the effects of drugs like Ozempic. The increases are orders of magnitude smaller than those seen with the drug, however.
In general, most researchers agree, sweaty exercise is more likely to help us with weight control – preventing weight gain – than weight loss.
But a stable weight is important, and exercise has its own unique and irreplaceable benefits. “The most important role of exercise,” says Stensel, “is to keep people fit, healthy and active enough to stay engaged with family, friends and society and therefore lead interesting and fulfilling lives. .”
Do you have a fitness question? Email YourMove@washpost.com and we may answer your question in a future column.