Sex Determines Effect of Exercise on Diet Preference
New research from the Department of Psychological Sciences suggests physical activity can change diet preferences in males, but not females. Jenna Lee, a fourth-year doctoral candidate in the lab of associate professor of psychological sciences Matt Will, says she was curious why we eat for pleasurable purposes instead of nutritional need. She says researchers have begun to look at how exercise might influence how males eat, though very little attention has been paid to the impact of physical activity on female diet preferences. Lee and Will set out to correct that oversight.
“I wanted to make sure we looked at female perspectives because most of the other papers neglected females,” Lee says. “What is driving diet preference and do environmental factors of physical activity play a role in that? And is there a difference between males and females?”
Diet and Exercise
Lee allowed a group of male and female rats to acclimate to her lab for a week before recording their weights. She then divided the rats into two groups—a sedentary group and a group that had access to a running wheel; both groups ate the same food. After another week, Lee replaced the standard diet with three optional diets: high fat (similar to cookie dough), high sucrose (three times more sucrose), and a high-cornstarch diet (matched for macronutrients, but with less sucrose). All of the diets were matched on proteins, and the rats had continuous access to all three diets at the same time for the next four weeks.
Lee says the fact that sedentary male rats preferred the high-fat diet was not surprising since it was the “tastiest” option and would have triggered reward centers in the brain. Male runners ate about half as much of the high-fat diet as their sedentary counterparts but increased their intake of the other two options. Female sedentary rats, like their male counterparts, mostly stuck to the high-fat diet. What is surprising, Lee says, is that female runners also preferred the high-fat diet and actually consumed slightly more calories than the sedentary females. The study also examined brain opioids and gut microbiota, discovering key changes that paralleled the patterns observed in diet preferences between male and female runners.
“I think this research draws attention to the importance of studying men and women in research, especially in studies of exercise and physiology,” she says. “One thought is females have an elevated threshold for rewards. Considering females demonstrate higher levels of reward signaling in the brain, this may possibly explain the higher threshold or capacity for reward. So perhaps something like running may be satiating for males but not for the females, so the females are consuming more of the high-fat diet. We expected to find differences between runners and sedentary rats, but it was the sex differences that surprised us.”