Body Weight and the Brain’s Response to Exercise

Do you thrive on exercise? Do you hate it? It turns out that the brain responds differently to exercise in lean versus overweight women, according to a new study. It was previously discovered that many overweight people’s brains operate differently than the brains of leaner people when they look at images related to eating. Now, researchers tested whether weight plays a role in how people view physical activity.

The study used a functional magnetic resonance imaging (MRI) machine, which scans blood flow to specific areas of the brain, indicating areas of increased activity. During the scan, women were shown a series of ninety images showing people enthusiastically exercising– running, dancing, leaping, playing tennis, etc. Researchers asked participants to vividly imagine they were performing the same actions, using hand gestures and limited bodily contortions, to the extent possible within the confines of the machine. Then, ninety additional images were shown, displaying relaxed, sedentary behaviors, like sitting in a desk chair and lounging on a couch. The participants were again asked to imagine themselves behaving similarly. The various images of activity and relaxation were mixed with photographs of landscape images.

The MRI readouts demonstrated that overweight women’s brains were “put off” by exercise.  When they viewed images of people being active, these women developed little activation in the putamen region of the brain, which suggests that they did not enjoy what they were seeing. In addition, an area of the brain related to dealing with negative emotions lit up far more when they looked at people moving than of people sitting. The results suggest that the overweight women anticipated disliking physical activity much more than they expected to disdain sitting. By and large, leaner women displayed the opposite brain activity, with the putamen lighting up when they watched others engage in activity and envisioned doing the same themselves.

While the findings may at first seem discouraging—pointing to the possibility that being obese or overweight is self-reinforcing–the study authors say that there was an encouraging finding. They found that when overweight participants viewed images of exercise, an area of their brain related to movement memory remained stubbornly silent. They speculate that it might be because their bodies were unfamiliar with how to be active, contributing to these women’s negative emotional response to activity; they didn’t know how to exercise and anticipated not enjoying trying to learn.

The practical takeaway from the study is to encourage people to pursue physical activity that they actually might enjoy. “If you continue to find yourself drawn to the couch instead of the gym, use that inclination strategically, such as a reward for increasing exercise,” said lead study author, Dr. Todd Jackson, a professor of exercise science at Southwest University. “Swim for 45 minutes and then allow yourself to surf the Internet. Don’t fight your brain’s unenthusiastic attitude toward exercise, embrace it,” he said.

We spoke with Dr. Laura Machado, expert weight loss surgeon in Sacramento, about the findings, and her theory on physical activity after weight loss surgery. She said, “The dramatic changes with bariatric surgery impact all areas of a patient’s life.  Patients are encouraged to exercise, but many find it painful or difficult in the beginning.  I encourage patients to just be “more active” to start with and build from there.  Some patients will never love the gym, but they may enjoy dance or outdoor activities.  Others want to get back to an activity or sport they once participated in.  The key is to keep trying, movement will get easier as the pounds are shed.  Comprehensive bariatric care involves helping our patients reshape their lives, not just their bodies.  It is a process.”

Other recent research suggests that exercise can influence appetite through altering how specific parts of the brain react to the sight of food. You can read more about the study here.

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