Plenty of people who are overweight or obese exercise their hearts out. It may not have an obvious effect on their body shape, and no doubt some wonder what’s the point of their effort.

An interesting new study – with a group of obese participants who regularly exercised, and another group who didn’t – goes some way to answering that question.

Short version: Those who had routinely exercised for at least two years had heathier belly fat and stored it more effectively and safely than those who hadn’t exercised.

Doesn’t sound like much of a big deal?

The participants may have superficially looked the same, as far as their body size went. But what was going on inside their bodies was radically different. And it mattered.

The study

Researchers from the University of Michigan wanted “to investigate the effects of years of regular exercise on fat tissue”.

Great idea, but one problem: It’s very difficult “to design a study to track this long term”.

And of course, there’s all that waiting around to see what happens.

Instead, they took a different approach, one that sort of answered the original question – but also looked at what happens when people with obesity exercise for a long time, and continue to be obese.

They assembled two teams of 16 participants who were obese or overweight. There were eight males and eight females in each group.

The members of one team had exercised at least four times a week, for two years, the average being 11 years.

Participants were closely matched for body fat percentage and fat mass, and were very similar in age, body weight, and body mass index.

Samples of subcutaneous adipose tissue (body fat) were taken and analysed from all participants.

The findings

Fat is stored in the human body in three places. First, it is stored under the skin in subcutaneous adipose tissue.

Second, there is the more dangerous visceral or abdominal fat cells that are deep inside the body. These may surround the organs. And third, there’s fat that accumulates inside organs, including the bones.

Of these three locations, subcutaneous adipose tissue is generally considered the least harmful.

The researchers found that the exercisers “had distinct structural and biological characteristics in their fat tissue” that increased the capacity to store fat subcutaneously.

Specifically, the exercisers “had more blood vessels, mitochondria and beneficial proteins”.

They also had less of a type of collagen that can interfere with metabolism and fewer cells that cause inflammation.

The non-exercisers did not have those beneficial characteristics.

Increasing the capacity to store fat subcutaneously through exercise “reduces the need to store fat in unhealthy places, like in the fat tissue around the organs or in the organs themselves”.

Jeffrey Horowitz, professor of movement science at the U-M School of Kinesiology was the principal investigator. In a prepared statement, he said:

“Our findings indicate that in addition to being a means to expend calories, exercising regularly for several months to years seems to modify your fat tissue in ways that allows you to store your body fat more healthfully if or when you do experience some weight gain – as nearly everyone does as we get older.”

He said it’s important to note that increasing the capacity to store fat does not equate to gaining fat. That would require overeating.

In follow-up studies the researchers will examine whether the fat tissue grown from exercisers and non-exercisers functions differently.