Inactivity in obese mice doesn’t stem from the extra weight they’re packing, according to a study published in Cell Press. Rather, it’s caused by altered dopamine receptors, linking obesity to the human brain as opposed to physical genetics.

“Other studies have connected dopamine-signaling defects to obesity, but most of them have looked at reward processing—how animals feel when they eat different foods,” Alexxai V. Kravitz, the study’s senior author and an investigator in the Diabetes, Endocrinology, and Obesity Branch at the National Institute of Diabetes and Digestive and Kidney Diseases, said. “We looked at something simpler: Dopamine is critical for movement, and obesity is associated with a lack of movement. Can problems with dopamine signaling alone explain the inactivity?”

This could explain why some people have more difficulty than others in sticking with an exercise program. 

“In many cases, willpower is invoked as a way to modify behavior,” Kravitz says. “But if we don’t understand the underlying physical basis for that behavior, it’s difficult to say that willpower alone can solve it.”

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