Want to get healthy? Try diet and exercise. Americans age 50 and younger — especially people with obesity — hear this recommendation frequently. But for older individuals healthy is more complicated.

“As metabolism declines, so do levels of physical activity,” explains Mayo investigator Nathan LeBrasseur, Ph.D. “The gain of fat is matched with the loss of skeletal muscle. Rapid weight loss may negatively affect the health of muscle and other organ systems. However, there isn’t a lot of data on which to base targeted recommendations for this group.”

Nathan LeBrasseur, Ph.D.

That’s why Mayo aging experts are looking into how to improve health in older adults who are overweight, beginning with animal models.

A new Mayo study published in Aging Cell helps to identify potential weight loss “red flags.” Though the study focuses on obese, elderly mice, it can be interpreted as a cautionary tale for those who try the recent trend of “time restricted feeding.” The authors report that exercise is still great, but restricting food intake to a limited period of the day may be an issue.

The study examined mice that, for their adult lives, were fed a diet designed to mimic human fast food. At 20 months of age (approximately equivalent to human age 60), the mice were split into three groups—one that was left sedentary, one that had access to an exercise wheel, and one that was put on a fasting diet with food only available for eight hours each day.

After four months of a restricted diet or opportunity to exercise, the mice were tested for a variety of health markers. The team looked at indicators of “body composition, physical function, task performance, metabolism, cardiovascular function, and morbidity;” all characteristics that are worsened by aging and exacerbated by obesity.

The results were mixed, with each intervention eliciting different health outcomes. While both fasting and exercise decreased body fat, only fasting improved cognitive ability, liver function, and glucose tolerance. Likewise, only exercise improved muscle mass and physical activity.

Importantly — and a key takeaway from this study — the fasting mice experienced a decline in muscle mass and more importantly, reduced cardiovascular function, two adverse effects not observed when fasting younger mice.

“The benefits of exercise are irrefutable and safe throughout life,” says Dr. LeBrasseur. “Until now, time restricted feeding has not been comprehensively assessed in older organisms. While there appear to be benefits in certain domains of health, the loss of lean mass and stiffening of vessels generates concern. The use of time restricted feeding as a strategy to improve the health of older adults challenged with obesity warrants further study.” - Calley Jones