In a groundbreaking study, scientists at The Jackson Laboratory (JAX) have delved into the relationship between diet, aging, and lifespan, shedding new light on how eating habits might influence longevity, and drawing both inspiring and fatalistic conclusions.
While the benefits of calorie-restricted diets have been researched and proven for nearly a century, the precise mechanics behind these effects have always remained unclear.
A long anticipated study, published on Wednesday in Nature, aimed to clarify these ambiguities by examining the health of 960 mice as they were submitted to various diets.
All the mice were selected to be genetically distinct, so as to mimic the genetic diversity of the human race and provide insights clinically relevant to human health.
The researchers assigned different diets to five groups of female mice.
One group was able to eat “ad libitum” and consume freely any amount of food at any time they wanted.
Another two groups were made to fast one day or two consecutive days per week.
And the remaining two groups were subjected to caloric restriction (CR) and given only 80 or 60 percent of their normal food intake each day, except on Fridays where they would get a triple ration but then no food on the weekend. The 60 percent CR group would consume their Friday ration by Saturday afternoon, while the 80 percent CR group would finish their Friday ration by Sunday afternoon.
This diet persisted while the mice were studied for the rest of their lives with periodic blood tests, regular assessment of body weight, grip strength, echocardiograms, wheel running performance, etc.
The results were striking: mice on the most restricted diets lived significantly longer, with those consuming only 60 percent of their normal calorie intake living a whopping 36 percent longer on average—34 months compared to 25 months for those eating ad libitum.
Those living on 80 percent of their normal food intake lived 20 percent longer: 30 months.
The mice on intermittent fasting lived for 28 months, a 12 percent lifespan increase.
However, as lifespan increased, so too increased the variability in lifespan. For instance, the 60 percent CR group had life spans ranging from a few months to 54 months.
“Our study really points to the importance of resilience,” Gary Churchill, professor at JAX who led the study, said in a press release. “The most robust animals keep their weight on even in the face of stress and caloric restriction, and they are the ones that live the longest.”
Surprisingly, the study indicated that factors traditionally associated with health and aging, like body fat and glucose levels, were less predictive of longevity than expected, and generally did not interfere with the diets’ positive effects on longevity. Instead, genetic factors such as the immune system’s health and traits related to red blood cells emerged as more significant indicators of lifespan.
Among those genetic factors, the researchers made special mention of genetically-coded resilience as a critical factor in extending longevity. Mice that naturally maintained their body weight, body fat, and immune cell vigor while on a restricted diet, as well as those that did not lose body fat late in life, survived the longest.
“While caloric restriction is generally good for lifespan, our data show that losing weight on caloric restriction is actually bad for lifespan,” Churchill said.
“So when we look at human trials of longevity drugs and see that people are losing weight and have better metabolic profiles, it turns out that might not be a good marker of their future lifespan at all.”
Further research will have to determine to what extent these results observed in mice correspond with human beings.