A Mouse Study On Intermittent Fasting and Caloric Restriction Left Researchers Scratching Their Heads

Eating may be one of life’s great pleasures, but when, how often, and how much we should be munching for optimal health is still a key question for scientists. The connection between eating and human health and longevity is an active area of research. A study out this week may get us one step closer to understanding why some people live much longer than others.

The new research studied nearly 1,000 genetically diverse mice who were placed on one of five diets: Eat as normal; fast for one day; fast for two days; eat 20 percent less than baseline; eat 40 percent less than baseline. Then, for the rest of the mice’s lives, the authors conducted about 200 assessments of immune, blood, metabolic, functional, and behavioral traits.

The researchers were trying to untangle what it is about dietary restrictions that makes people live longer. Is it less weight? More stable blood glucose levels? Low body fat percentage? Or something else that we’ve been overlooking?

The study found that those left on their normal diets where they could eat whatever they wanted lived, on average, for 25 months. Mice that fasted for one day or two days a week lived for 28 months, while the mice that ate 20 percent less lived for 30 months and the ones that ate 40 percent less lived for 34 months. These findings published today in the journal Nature.

What was most confusing to the researchers was that each group had a wide range of lifespans with some mice living a few months and others, in each group, living a much longer life, up to four and a half years. To try to identify what was behind these longer living mice, the researchers found something they dubbed “resilience:” Mice that were able to keep the same body weight, fat percentage, and immune cell health throughout their lives — and importantly, during times of low food intake or other stressors — lived the longest.

The study also found that for these mice, just maintaining a low body weight, body fat percentage, or low glucose level throughout life — which has long been thought to play a role in longevity — wasn’t directly associated with a longer life. The researchers surmise that there must be a genetic factor underlying these abilities, and it could be key to living a long life.

So where does this leave us? Well, first, as with anything in science, more research is needed to confirm these findings. Second, because its a mouse study, its much harder to say what the results mean for humans. Very likely, scientists will need to do similar studies in humans. The authors write that further work also must disentangle the physiological effects of dietary restrictions on humans, which will change in every person. Despite this study’s limitations, it provides significant insight that while diet can increase longevity, genetics might still win.