Clients often tell me that once they start exercising, healthier eating follows with less effort. I assumed this was due to self-talk such as “I’m not going to mess up my great exercise regimen with unhealthy foods.” But a recent study in Obesity Biology and Integrated Physiology (March 2018) provided new food for thought.
It is known that physical activity alters post meal appetite hormones leading to decreased hunger and food intake. These researchers from UCLA went further and examined how physical activity might impact brain systems involved in processing food reward.
There were 40 healthy subjects in this study. All were in their 20s and half were lean, half obese. Subjects were given activity questionnaires and then categorized as engaged in moderate to vigorous physical activity (MVPA) or sedentary behavior (SB). Before their MRIs, subjects were given a glucose load. This was to mimic a fed situation. During the functional MRI, participants saw cards with pictures of high calorie foods such as cookies and pizza and control cards with pictures of books and baskets. The MRI measured brain signal change in response to the food and nonfood pictures.
Greater MVPA was associated with decreased brain response to high calorie food cues. Greater SB was associated with increased food cue reactivity. These results were the same in the lean and obese individuals. The quick translation is that the brains of people who sit more, whether at work or on screens, have a greater reaction to higher calorie foods. So maybe what I am hearing from clients about healthier eating after exercise is related to how their brains have a lower response to higher calorie foods. For each additional 30 minutes of SB, the average for high calorie food cue reactivity increased by 0.012 percent. That might seem small, but add up all your sitting hours in a day and you have a clue of why the office treats might be looking more tempting.
With apologies to the brilliant Bob Marley, “get up stand up stand up for your thighs.”
Sheah Rarback is a registered dietitian on the faculty of the University of Miami Leonard M. Miller School of Medicine. Follow her on Twitter @sheahrarback.