- Exercise has a complex relationship with appetite that may make you feel hungry or satiated.
- New research indicates that high-intensity exercise could mitigate feelings of hunger, particularly in women, by decreasing ghrelin levels.
- Ghrelin, popularly referred to as the “hunger hormone” stimulates appetite and signals when the stomach is empty.
High-intensity exercise appears to play an important role in mitigating feelings of hunger, according to a new small study. Those findings were even more prominent among females.
The research, published online on October 24 in the Journal of the Endocrine Society, investigates the complex relationship between exercise, the hormone ghrelin, and perceived hunger.
Ghrelin is popularly known as “the hunger hormone,” due to its ability to stimulate appetite. Researchers also sought to fill in gaps in the literature, specifically related to sex. While there is plenty of research available on exercise and appetite, the study authors note that little of it involves females.
Additionally, prior studies have typically utilized only one form of ghrelin, known as acylated ghrelin (AG), but this latest research offers a more complete picture by including a second form, deacylated ghrelin (DAG).
“The key take-home message from the study is that exercise, particularly at a higher intensity, suppresses total, acylated, and unacylated ghrelin, and this effect appears to be more pronounced in women than men,” Alice Thackray, PhD, a senior research associate in exercise metabolism at Loughborough University who wasn’t affiliated with the research, told Healthline.
Both Thackray and the study authors acknowledge there is still much more to learn about the effects of exercise on appetite, but the study helps to confirm prior findings across sex and hint at a potential mechanism.
How exercise affects the ‘hunger hormone’
Your body is constantly burning calories, even when at rest. When you exercise, your body’s energy requirements ramp up too, burning more calories, which can make you feel hungry. But that isn’t always the case.
Unintuitive though it may seem, exercise can also suppress hunger. The exact reasons for this aren’t entirely certain, but researchers have homed in on the impact of exercise on circulating ghrelin.
In their study, researchers investigated this relationship utilizing 14 adults — eight of them male and six female. The participants were younger adults; the average age for men was 43 years old and 32 years old for women. Participants were not overweight, with both groups having an average body mass index (BMI) of about 22.
Each participant had three randomized visits of exercise. During their visit the participant would take part in no exercise, moderate exercise, or high intensity exercise.
Baseline and post-exercise measurements were taken for AG, DAG, total ghrelin, and lactate. Lactate is a metabolic byproduct that builds up during exercise and serves as a biological marker of muscle fatigue.
Participants also had to answer questions about their appetite, fullness, and desire to eat to create a composite score of perceived hunger.
In both groups, high-intensity exercise suppressed DAG, but women, whose baseline ghrelin was already higher than men, showed a dramatic drop in AG.
“The decrease in acetylated ghrelin after high intensity was really driven by the female group,” Kara Anderson, PhD, first author of the study and postdoctoral fellow at the University of Virginia School of Medicine, told Healthline.
However, decreased ghrelin levels didn’t clearly correlate with a similar drop in perceived hunger for either group.
“The hunger scores in response to exercise are pretty similar between men and women. So, there’s still a lot of research to be done, but this does suggest that males and females may respond to exercise differently, especially considering their ghrelin levels,” said Anderson.
Why exercise intensity matters
The impact of exercise on hunger and ghrelin levels varied across exercise intensity. High-intensity exercise had the most significant effect on ghrelin across males and females. However, perceived hunger told a different story.
For females, both high-intensity and moderate-intensity exercise resulted in nearly identical hunger scores, both of which were higher than the control (no exercise). For males, high-intensity exercise resulted in diminished perceived hunger compared to the control, while moderate exercise resulted in increased hunger.
But the most important aspect of high-intensity exercise may have to do with lactate, which the authors theorize could be involved in “exercise-induced ghrelin suppression.”
Essentially, when you exercise, your body builds up lactate as a byproduct. When your body produces lactate faster than it can be used aerobically, your body has crossed what’s known as the lactate threshold.
To cross the lactate threshold, you have to be engaged in high-intensity exercise. And it may be the presence of lactate from crossing that threshold that is key for mitigating hunger.
“The exercise-induced changes in ghrelin were observed alongside increases in lactate which has been proposed previously as a potential mechanism for ghrelin suppression with exercise,” Thackray said.
“We need more research to support the mechanisms involved in exercise-related appetite responses, including how exercise influences appetite regulation within the brain,” she noted.
Takeaway
Exercise has a complex relationship with appetite that can both stimulate and suppress hunger.
New research indicates that both exercise intensity and sex are factors for the effects of exercise on appetite.
In their study, researchers from the University of Virginia found that high-intensity exercise resulted in significantly diminished levels of ghrelin, popularly known as the “hunger hormone.”
The effects were more pronounced in females compared to males. More research is needed to better understand the mechanisms involved in exercise-related appetite responses.
