Health. Why do we get a belly as we age? Scientists may have found the answer.

Are we doomed to gain a belly as we age? A study published in the journal Science seems to support this view and reveals an unsuspected culprit: with age, a new type of adult stem cell appears that promotes the massive production of new fat cells (adipocytes), particularly around the abdomen.

"It's common to lose muscle and gain fat as we age, even if we maintain a constant weight," says Dr. Qiong Wang of City of Hope National Medical Center in California, a co-author of the study.

Of Mice and Men…

For their experiments, the researchers first transplanted stem cells called "adipocyte progenitor cells" from young and old mice into another group of young mice. Adipocytes are cells that store fat in the body.

The surprising result: cells from older animals quickly generated a colossal amount of fat cells, regardless of their host's age. However, when the team transplanted fat stem cells from young mice into older mice, the stem cells did not produce many new fat cells.

The authors then observed that aging transforms these stem cells into a new type called CP-A (for "committed preadipocytes, age-specific"). Appearing in middle age, these CP-A cells actively produce new fat cells, explaining why older mice gain more weight.

"While the growth capacity of most adult stem cells decreases with age, the opposite is true for adipocyte progenitor cells: aging releases their capacity for evolution and multiplication," the authors continue.

Results confirmed in humans

The team then studied human tissue samples of various ages. They identified CP-A cells, which are more numerous in the tissues of middle-aged people. This discovery shows that these cells also have a high capacity to create new fat cells in humans.

"Understanding the role of CP-A in metabolic disorders and how these cells appear with aging could open the way to new medical solutions to reduce abdominal fat and improve health and longevity," the researchers conclude.