The study, conducted on mice, has been published in the journal of Cell Metabolism.
“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’s senior author Alexxai V. Kravitz from the National Institute of Diabetes and Digestive and Kidney Diseases in the US.
“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 added.
Based on that observation, he hypothesised that the reason the mice were inactive was due to dysfunction in their dopamine systems.
In the study, mice were fed either a standard or a high-fat diet for 18 weeks.
Beginning in the second week, the mice on the unhealthy diet had higher body weight.
By the fourth week, these mice spent less time moving and got around much more slowly when they did move.
The findings indicated that the mice on high-fat diet moved less before they gained the majority of the weight, suggesting that the excess weight alone was not responsible for the reduced movements.
The investigators looked at six different components in the dopamine signaling pathway and found that the obese, inactive mice had deficits in the D2 dopamine receptor.
“There are probably other factors involved as well, but the deficit in D2 is sufficient to explain the lack of activity,” said first author Danielle Friend.