People who are overweight may find it more difficult to take part in physical exercise due to a chemical imbalance in the brain, according to new research.

A new study conducted by researchers at the National Institutes for Health (NIH) has found people who are obese due to diet have certain changes in the dopamine levels within the brain that depletes motivation to exercise.

Dopamine is an essential chemical that affects mood, appetite and motor control and the researchers looked at lab mice with lean body mass. What they found was when dopamine levels were lessened in the brains of the mice, so was their motivation to be active.

“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. 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,” explained lead author of the study Dr Alexxai Kravitz from the NIH.

This explains the lack of willpower in overweight people rather than a ‘lazy’ view of obese people unwilling to tackle their weight problem.

“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.” 

“Exercise is a healthy thing to do, but its impact on weight has been overstated. We have to be realistic about the size of the effect of exercise on weight, as opposed to health benefits,” Kravitz went on to explain.

Details of the study can be found in the journal Cell Metabolism.