Regular exercise and a healthful diet are key for maintaining good health. Now, a new study sheds light on how the former affects the latter, after finding that physical activity could alter men's diet preferences.
The diet preferences of women, however, are likely to remain unaffected by exercise, according to the findings.
Study co-author Jenna Lee and colleagues from the University of Missouri in Columbia recently reported their results in the journal Behavioural Brain Research.
The effects of exercise on diet have long been of interest to researchers, and previous studies have indicated that physical activity can encourage us to make more healthful food choices.
But Lee and team note that few of these studies have investigated how the dietary effects of exercise might differ by sex.
"Our team wanted to make every effort to study female perspectives on how exercise affects diet, because most other studies neglect females," says Lee.
"We wanted to take a look at what drives diet preference and if environmental factors, such as physical activity, play a role in how males and females eat."
Exercise vs. sedentary behavior
To reach their findings, the team studied male and female rats by splitting them into two mixed-sex groups: one group had access to a running wheel (the exercise group), while the other did not (the sedentary group).
For the first week of the study, both groups ate the same standard diets. At week 2, the standard diet was replaced by a choice of three diets: a high-fat diet, a high-sucrose diet, and a high-cornstarch diet. All diets contained the same amount of protein.
The rats had constant access to each of these diets for a total of 4 weeks.
The researchers found that both male and female rats that were sedentary showed a preference for the high-fat diets over the high-sucrose and high-cornstarch diets.
Interestingly, in the exercise group, the team found that male rats demonstrated a change in the diets, while female rats did not.
While exercising female rats continued to opt for the high-fat diet over the other two diets, exercising male rats reduced their intake of the high-fat diet and increased their intake of the high-sucrose and high-cornstarch diets.
"We expected to find differences between runners and sedentary rats, but it was the sex differences that surprised us," says Lee.
Gut and brain differences found
On assessing fecal samples from each group before and after the 4-week diet preference period, the researchers identified differences in gut microbiota between male and female rats in the exercise group. This indicates that gut microbes may play a role in sex-dependent dietary responses to exercise.
Additionally, by analyzing the brains of rodents in the exercise group, the team discovered differences in reward-related opioid mRNA expression between male and female rats.
"Considering females demonstrate higher levels of reward signaling in the brain, this may possibly explain the higher threshold or capacity for reward," Lee suggests.
She adds that running may satisfy hunger in males, but not in females, which may encourage females to opt for high-fat foods.
Taken together, the researchers believe that their findings indicate that the dietary preferences of males and females largely differ in response to exercise.
"The significant sex differences in response to physical activity observed through both behavioral and physiological measures suggest potential motivational or metabolic difference between males and females."
"The findings highlight the necessity for further exploration between male and female response to physical activity and feeding behavior," the team concludes.