New research by a multidisciplinary team of University of Missouri researchers suggests that physical activity can change diet preferences in males, but not in females. According to Jenna Lee, a doctoral candidate in the Interdisciplinary Neuroscience Program at MU, "Our team wanted to make every effort to study female perspectives on how exercise affects diet, because most other studies neglect females... 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." As it turns out, the study discovered that the very act of exercising is enough to help males make better diet choices.

In the study, male and female rats were divided into two groups, a sedentary group and one that had access to a running wheel. Both groups ate the same food at first, with the standard diet replaced with three optional diets after one week had passed. The rats had a choice of eating a high fat diet similar to cookie dough, a high sucrose diet, or a high-cornstarch diet. Each of the diets were matched on proteins, with the rats having continuous access to all three diets over a four week period. Results showed that sedentary male rats preferred the high-fat diet over the other diets, with male runners eating about half as much of the high-fat diet as their sedentary counterparts. While female sedentary rats mostly stuck to the high-fat diet like their male counterparts, surprisingly, female runners also preferred the high-fat diet and actually consumed slightly more calories than sedentary females.

According to the study, these results can be explained by differences in brain chemistry and gut bacteria: "We also examined brain opioids and gut microbiota, and we discovered key changes that paralleled the patterns observed in diet preferences between male and female runners. A reason for this might be that females have an elevated threshold for rewards. Considering females demonstrate higher levels of reward signalling in the brain, this may possibly explain the higher threshold or capacity for reward. 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."

It's not all bad news for active females, however, with a separate study from Indiana University highlighting a known phenomenon called the 'transfer effect'. As it turns out, learning new skills and improving in one area of your life automatically triggers a desire for improvements in other related fields, with exercise improving diet choices and vice versa. In a study of more than 6,000 people born between 1980 and 1984, a distinct correlation was found in both males and females between the amount we exercise and the amount of fresh produce we consume. There are two main reasons for this correlation, with exercise and diet linked with the same overall goal in the brain, and exercise helping the brain to make better diet choices.

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