Bodyweight Control May Depend on Sex

Exercise might not be equally effective in males and females, according to research.

Studies in the past have investigated differences in physiological response between men and women. Men tend to have higher muscle mass, while women’s bodies require more fat to be healthy. Being aware of these differences between men and women will help you have realistic expectations when training, either for weight loss, muscle growth, or overall fitness.

Here’s a new difference: exercise has more visible effects on men than women, according to one study’s results using male and female rats. A team of researchers from the University of Colorado, Anschutz Medical Campus subjected male and female rats to ten weeks on a high-fat diet. Half of each group ran on a treadmill for those ten weeks.

At the end of the testing period, the rats were analyzed for weight and food intake. The female rats that exercised didn’t decrease their food intake. Their weight was the same as the sedentary rats by the end of the testing period. The male rats, however, ate less when they exercised and gained less weight. Even with a high-fat diet, the male rats gained less weight than the rats that didn’t run.

When repeating the test, this time with a low-fat diet, the male rats that ran exhibited a visible impact far more quickly than the female group. The male rats that exercised significantly decreased their body weight compared to the male rats that followed a low-fat diet and didn’t exercise.

A previous study discovered that exercise (even one session) led to an increase in interleukin-6 (IL-6). This neurochemical, produced in the hypothalamus, plays a role in body weight regulation, as it enhances the brain’s response to appetite and food intake hormones, essentially suppressing them.

When testing IL-6 among the rats in this study, the researchers found that levels increased among the female rats that exercised. The male rats that exercised saw a decrease in their production of this neurochemical.

Rebecca Foright, who led the study, is calling for more gender-specific studies of the effects of exercise:

“Despite an increased prevalence of obesity in women and physiological differences between males and females in the hormonal signals and brain processes that influence appetite, the vast majority of mechanistic studies on obesity and treatment are performed in male animals… It is unacceptable to simply assume that females will respond to interventions in the same manner as males.”