Chung and his colleagues looked for molecular changes that occurred in animals during middle age and found that an enzyme called DNA-dependent protein kinase, or DNA-PK, increases in activity with age.
Their research showed that this enzyme is involved in metabolism (such as the conversion of nutrients to fat) and in the production of mitochondria, or the "powerhouses" in cells that turn nutrients into energy. It's known that as people age, they see a drop in the number of mitochondria.
In the study, the researchers found that giving mice that were on a high-fat diet a drug that inhibits DNA-PK led to a weight gain in those mice that was 40 percent less, compared to mice that were also on this diet but didn't receive the drug.
In addition, mice that received the drug saw an increase in the number of mitochondria in their skeletal muscle cells, and experienced increased aerobic fitness.
"Our studies indicate that DNA-PK is one of the drivers of the metabolic and fitness decline that occurs during aging, which makes staying lean and physically fit difficult" in older age, Chung said.
However, the researchers noted that the findings don't mean people should abandon diet and exercise as they get older, since these are still the primary tools for fighting obesity. Middle-age adults should continue with these practices, even if it takes a while to see results, they said.
The study was published in the May issue of the journal Cell Metabolism.