Moderate exercise may help regulate appetite in obese men by influencing key hormones like IL-6, irisin, and NPY, offering potential insights for weight management strategies.

Study: Acute effect of exercise on appetite-related factors in males with obesity: A pilot study. Image Credit: Piyawat Pansirimongkonkun / Shutterstock.com

The obesity epidemic, which affects over one billion people worldwide, presents an ongoing challenge to public health. Eating behaviors are considered one of the major factors that contribute to the development of obesity.

Appetite is regulated by both environmental and intrinsic factors acting on the brain. A recent study published in Physiological Reports examines how appetite-associated factors impact appetite perception in obese males.

Obesity and appetite hormones

Gastrointestinal hormones have been extensively explored for their role in regulating exercise-induced changes in appetite. Recently, the role of interleukin 6 (IL-6), IL-7, irisin, and leptin released from muscle cells, fat deposits, and inflammatory cells in appetite-regulating pathways, have been explored. For example, the release of leptin from skeletal muscle has been shown to directly affect energy regulation, with rising leptin levels implicated in feelings of satiety.

Neuropeptide Y (NPY) is the most important neuropeptide associated with increased appetite in the central nervous system (CNS). However, it remains unclear whether the systemic circulation of NPY is involved in appetite behaviors.

The body responds differently to appetite hormones in obese and lean people. For example, lean people experience satiety after moderate continuous aerobic exercise that is accompanied by altered gastrointestinal hormone levels; however, these effects of exercise have not been observed in obese individuals.

To date, few studies have examined fluctuations in appetite hormones and other appetite-related factors involved in obesity. Nevertheless, some evidence suggests that obese and overweight individuals experience a loss of appetite after moderate exercise.

About the study

The present study is the first to assess the short-term effects of moderate aerobic exercise on hormone and cytokine levels in obese individuals. The study cohort comprised 11 males with a mean body mass index (BMI) of 35.3 kg/m² and peak oxygen consumption (VO2peak) of 29 mL/kg/min.

The first MICE trial involved cycling at 60% of VO2peak, whereas control participants rested quietly for 60 minutes. The investigators examined how hungry participants felt before breakfast, 30 minutes after breakfast, and at half-hourly intervals after exercise until 1:15 AM. IL-6, IL-7, irisin, NPY, and leptin levels were measured in all study participants.

Study findings

Acutely increased post-exercise IL-6 and irisin levels were observed in the MICE group as compared to those in the resting group, as well as compared to fasting and pre-exercise levels. These concentrations remained high one hour after exercising.

NPY levels decreased at one hour as compared to fasting or pre-exercise levels. No significant change was observed in IL-7 or leptin levels.

Study participants in the MICE trial felt less hungry immediately after exercise, as well as one hour after exercise, as compared to controls.

Comparison with prior studies

The reported rise in IL-6 levels confirm earlier findings in obese subjects; however, the IL-6 response appears to vary with the number of muscles used during exercise and exercise duration. With continued exercise, glycogen reserves in muscle tissue are primarily consumed in slow-twitch fibers, thereby stimulating IL-6 release.

IL-6 levels rose one hundred-fold after exercise. Since IL-6 enters the circulation, it may cross the blood-brain barrier to affect appetite after exercising. In earlier studies, systemic injection of IL-6 at a dose equal to four-fold normal levels significantly reduced food consumption, thus indicating its potential role in exercise-induced appetite loss.

The 20% increase in irisin levels similarly agrees with previous reports, with the release of this hormone likely dependent on the duration of physical activity. Notably, irisin levels are naturally higher in obese individuals due to irisin resistance.

The reduction in post-exercise NPY levels contradicts earlier results. NPY is secreted by multiple cell types in the body, increases with greater exercise duration, and is present at higher concentrations in obese or overweight individuals.

The reduction in appetite after exercise is not uniformly reported in all studies and may vary with stress, mood, and the individual’s perception of the degree of exertion. The study findings suggest that changes in appetite after exercise may be attributed to rising IL-6 and irisin levels that are accompanied by lower NPY levels.

Conclusions

The study findings reflect a dynamic shift in several myokines and cytokines following moderate continuous exercise in obese men. The effect of these changes may reduce appetite; therefore, targeting these hormones has the potential to effectively reduce weight and achieve energy balance in obese men.