How eating less may help extend life span

For this study, researchers used 960 genetically diverse female mice that were assigned to five different diets:

• calories limited to 60% or 80% of baseline calories each day
• fasting for one or two consecutive days each week with no caloric restrictions
• eating any amount of food whenever it wanted

“We wanted to know if lifespan-extending interventions like caloric restriction or intermittent fasting could be beneficial for everyone or only for some people. This is hard to do with people, so we turned to a genetically diverse mouse model,” Gary Churchill, PhD, Karl Gunnar Johansson Chair and professor at The Jackson Laboratory and senior author of this study, explained to Medical News Today.

“Caloric restriction is known to extend life span in rodents since its discovery in rats in the 1930s, however it is still not fully understood how this works,” added Andrea Di Francesco, PhD, principal scientist at Calico Life Sciences LLC and lead author on this study. “Recent studies have shown that the timing of feeding is important in addition to reduced caloric intake.”

“Additionally, recent studies have suggested that in mice, some individuals (genotypes) may have reduced life span on caloric restriction. We were interested in determining how universal life span extension on caloric restriction is and if the benefits depended on the strength of caloric restriction (20% vs 40%),” Di Francesco told MNT.

At the study’s conclusion, scientists found that while mice who could eat whenever and whatever lived an average of 25 months, those on intermittent fasting diets extended their lifespans for an average of 28 months.

The mice on caloric restriction achieved the longest lifespans — mice eating 80% of their baseline calories lived an average of 30 months, and those eating 60% stayed alive an average of 34 months.

“We were surprised that the extreme (40%) caloric restriction extended life span to such a great extent with no indication that it shortened life span of any mice. We assumed that in a genetically diverse population — a unique feature of our study — some animals would have reduced life span on 40% caloric restriction or on a two-day intermittent fasting routine,” Churchill said.

Researchers also discovered that genetic factors — such as genetically encoded resilience — played a larger role in longevity than diet in the mouse model.

“In mouse studies where we can control the environment, we see a strong genetic contribution. The genetics gives us a ‘ruler’ to evaluate how impactful the diets are — despite the dramatic life span extension e.g. on 40% caloric restriction, there is still a lot of individual variability (genetic and random). In other words, diets are not magic bullets — they increase average life span but do not guarantee long life for an individual. There are other factors that contribute at least as much to life span,” Di Francesco explained.

Scientists reported mice that naturally kept the same body weight, body fat percentage, and immune cell health during periods of reduced food intake and stress, as well as mice that did not lose body fat later in life, lived the longest.

“It has been proposed that caloric restriction works to extend life span by reducing obesity and prediabetes traits in mice. Improving metabolic health is important for humans in modern societies, and so it seems reasonable to think that life span extension in mice might be due to reducing obesity and its negative health effects,” Churchill said.

“This seems to not be the case — life span extension was greater in mice that retained higher body weight. Weight loss is ‘good’ from a human perspective, but weight loss does not cause life span extension — they are distinct outcomes of caloric restriction,” he added.

After reviewing this research, Mir Ali, MD, a board certified general surgeon, bariatric surgeon, and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA, told MNT what was interesting about the study is it showed lower calories or eating less increased life span, but not necessarily losing weight, which he found to be counterintuitive.

“You would think that if you eat less, you would lose weight and therefore extend your life span, but it was more about restricting the calories and losing weight in mice, at least — I don’t know how well that translates to humans. Animal studies are a great place to start, but obviously animals are a lot different than humans. And we need to see that the research done in animals translates to humans as well,” Ali continued.

MNT also spoke with Monique Richard, MS, RDN, LDN, a registered dietitian nutritionist and owner of Nutrition-In-Sight, about this study.

“I was not surprised by the results of the study because of what we are learning regarding cell turnover and optimal function related to lower-calorie diets, fasting, and other manipulations of distribution and quantity of intake,” Richard said.

During this study, researchers found that genetics and genetically encoded resilience might be unmodifiable factors in longevity. What can readers do to improve the aging process and maybe even increase their life span, whether through diet or other options?

“Your genetics plays a big role, obviously, but you want to avoid things that are going to counteract genetics (such as) obesity (and) eating unhealthy,” Ali explained. “Even if you have good genes, but you don’t do the right things, you can counteract that, so you obviously want to continue to eat healthy and maintain a normal weight to maximize your genetic potential.”

“The body is in a constant state of self-regulation, always trying to find a balance of being ‘just right’ — humming on all cylinders,” Richard detailed. “When the body has adequate nutrients to support all its cellular functions, for all the systems to work in specific amounts, at regular times, in appropriate intervals, it is like a machine functioning at its peak, or in the ‘zone,’ likely increasing its ability to function longer, hence likelihood of connection to increased life span.”

“Tips to possibly optimize diet in order to increase lifespan would be to prioritize understanding what this may mean specifically for you and your needs by meeting with a registered dietitian nutritionist (RDN. It is important to understand what the baseline of energy and distribution your individual body would need to be, especially related to preventing unnecessary or dangerous restriction, an imbalance of nutrient distribution or disordered eating patterns and behavior. There is no ‘magic formula’ to be calculated that works for everyone.”
— Monique Richard, MS, RDN, LDN