Vigorous exercise suppresses hunger more effectively than moderate activity, particularly in females. 

In a recent study published in the Journal of the Endocrine Society, researchers explored the effects of exercise intensity on levels of ghrelin (a hormone produced in the stomach associated with hunger) and appetite.

Their results indicate that high-intensity exercise could reduce ghrelin levels, leading to better management of hunger, with this response varying between men and women.   

Background

Ghrelin is a hormone primarily produced in the stomach, though other parts of the body also release it in small amounts. First isolated in 1999, it is often called the ‘hunger hormone’ and binds to the growth hormone receptor. It was initially known for stimulating the release of the growth hormone GHSR1a, but other functions have been discovered, including the regulation of appetite, energy, glucose, sleep, immune function, and memory.

The hormone exists in two forms. Deacylated ghrelin (DAG) is the most abundant form, accounting for approximately 78%, and either suppresses or has no effect on appetite, while acylated ghrelin (AG) is less abundant but actively binds to GHSR1s to stimulate appetite.

Acute exercise, undertaken at the right intensity, can reduce appetite, possibly through effects on ghrelin. Research linking appetite to ghrelin and exercise remains limited, but high-intensity exercise may increase blood lactate, thus suppressing AG and, consequently, appetite.

Current studies have focused on moderate intensity exercise and study populations of healthy young men, but the effects on women may be influenced by estrogen. Identifying the optimal intensity of exercise could support weight management plans for men and women.

About the study

In this study, researchers investigated how the intensity of exercise affects ghrelin levels and appetite in males and females, hypothesizing that high-intensity exercise would most significantly decrease AG and suppress appetite, with females showing higher overall ghrelin levels than males.

Participants in the study were between 18 and 55, did not smoke, had a body mass index (BMI) between 18.5 and 24.9, and had not experienced significant changes in weight in the past three months. They did not have diabetes or hormonal or gastrointestinal disorders and were not on medications that affect hormone levels or exercise.

They fasted and refrained from tobacco, caffeine, alcohol, and intense activity before measurement sessions. After a screening process where body fat, peak oxygen consumption, and lactate threshold were determined, participants took part in three sessions: a control where they did not exercise, a session of moderate exercise at the lactate threshold, and a high-intensity session at 75% between their lactate threshold and peak oxygen consumption.

Blood lactate was analyzed immediately after the sessions, while total ghrelin, AG, and DAG were preserved to be tested later.

Findings

Six females, with an average age of 32.2, and eight males, with an average age of 43.1, participated in the study. While females showed higher body fat percentages, triglycerides, and baseline DAG, males showed higher energy expenditure during exercise and peak oxygen consumption.

Total ghrelin levels were significantly lower in high-intensity exercise than in moderate-intensity or control, decreasing over time, particularly between 40 and 180 minutes after exercise sessions. Total ghrelin was lowest for women during high-intensity exercise and lower than for men.

AG levels were lowest in the high-intensity exercise and decreased significantly between 40 and 180 minutes after exercise. Women showed a greater AG decrease during high-intensity exercise, but males had no significant differences. DAG was lower in high-intensity exercise than in the other two, with females having lower levels than males.

Lactate was also highest in high-intensity exercise, with elevated LAC levels observed between 10 and 90 minutes after exercise. Moderate-intensity exercise was associated with the highest hunger score, but there was no significant difference between the other two.

Satisfaction decreased over time, especially in moderate-intensity exercise, though not significantly. Fullness dropped slightly by 180 minutes but showed no significant differences between conditions. Desire to eat was higher in moderate intensity than the control and reduced between 150 and 180 minutes after exercise. However, total appetite was lowest for the control and reduced over time.

Overall, ghrelin was positively correlated with the desire to eat and hunger, while AG and TG were inversely related to satisfaction and fullness and positively linked to appetite. In males, TG correlated positively with hunger, desire to eat, appetite, and body fat percentage but negatively with satisfaction and fullness. In females, AG positively correlated with hunger and negatively with satisfaction and fullness. Body fat percentage was negatively correlated with hunger and appetite.

Conclusions

These findings highlight important differences between males and females regarding the effects of exercise on appetite suppression. Further research can examine the influence of obesity and use chronic exercise programs to create tailored exercise guidelines for the prevention and management of obesity.