Mouse Study Hints at Why Obese People Struggle to Exercise

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Overweight mice may provide a hint as to why it’s so hard to start — and stick to — your New Year’s resolution to exercise more.

Researchers found signs that the brains of obese mice may encourage inactivity.

“We know that physical activity is linked to overall good health, but not much is known about why people or animals with obesity are less active,” said study senior author Alexxai Kravitz.

Kravitz is an investigator in the diabetes, endocrinology, and obesity branch of the U.S. National Institute of Diabetes and Digestive and Kidney Diseases.

“There’s a common belief that obese animals don’t move as much because carrying extra body weight is physically disabling. But our findings suggest that assumption doesn’t explain the whole story,” Kravitz said.

Kravitz has theorized that the brain chemical dopamine is key to inactivity in mice.

“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,” Kravitz said.

“We looked at something simpler: Dopamine is critical for movement, and obesity is associated with a lack of movement,” he said. His team wondered if problems with dopamine signaling alone could explain the inactivity.

For the study, researchers fed normal and high-fat diets to mice. The mice on the high-fat plan put on weight and slowed down. But they slowed down before adding pounds, raising questions about why things happened in that order.

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