Why Thin People Might Eat More and Still Stay Slim: 'It's Not Just the Fact that They're More Active

Much to the ire of those who exercise, eat right and still struggle with their weight, there are those individuals who can eat the same -- if not more -- work out the same amount and still be thinner. It would appear that it just comes naturally to them -- and a new study confirms this could be the case.

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"What is different about these people?" Dr. Colleen Novak, a biological sciences professor at Kent State University whose research focuses on the neuroscience of obesity, asked.

Kent State University researchers say that the current obesity epidemic -- about one-third of adults are overweight and one-third are obese -- is likely the result of our lifestyles but genes also play a part.

To see how genetics could impact obesity, researchers bred rats with specific genes that were linked with either high activity or laziness. They found that those rats known to be more active, based on their genetic breeding history, would burn more calories when exercising that fat rats doing the same amount of exercise. The active rats were also more likely to move around frequently during the day.

"It's not just the fact that they're more active that matters but also that they are burning more calories during activity," Novak said, noting that these extra calories are being "wasted" by the thin rats as heat.

"What is different in the brains of these rats that make them more active versus less active?" she asked.

Researchers found thin rats produced more receptors that would stimulate the area of the brain that would cause them to choose to be active. Fat rats on the other hand produced less of these receptors.

Thus, Novak told the university's news site that the fat rats don't move around less because they're overweight but because their brain function. Researchers are not yet sure why thin rats produce more of these receptors that would lead to activity than fat rats.

None of this is to say that rats predisposed to be overweight can't avoid this tendency. Conversely, rats with genes that would suggest they should be thin won't necessarily mean be thin in reality.

“In the bigger picture, [the study] would also imply that any advantage these intrinsically lean people have in staying thin may be canceled out if they are not physically active,” Novak said, according to Healthline News.

This study was published in the journal Endocrinology and Metabolism.