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BAR HARBOR, Maine — Can eating less really help you live longer? A new study says yes, but with a crucial twist. Scientists have found that it’s not just about cutting calories but how well your body adapts to dietary changes that truly matters for longevity.
The study, published in Nature, showed how different forms of dietary restriction can significantly extend the lifespan of mice. Researchers say their findings not only confirm the life-extending benefits of calorie restriction but also reveal that intermittent fasting can have similar effects, even without reducing overall calorie intake.
Led by scientists from Calico Life Sciences and The Jackson Laboratory, the research involved an extensive examination of 937 genetically diverse female mice. The rodents were split into five dietary groups: one with unrestricted access to food, two with calorie restrictions (60% and 80% of baseline calories), and two with intermittent fasting (one or two consecutive days per week without food). The mice were then monitored throughout their lives, with regular health assessments and blood tests.
The study found that both calorie restriction and intermittent fasting extended the lifespan of mice, with effects proportional to the degree of restriction. Mice on 40% calorie restriction lived about nine months longer than those allowed to eat as much as they wanted. That’s equivalent to extending a human lifespan by over a decade!
Even more intriguing, mice that fasted for one or two days per week also experienced significant lifespan extensions, with those fasting for two days living longer than those fasting for one. That’s despite consuming nearly the same amount of food overall as their unrestricted counterparts.
The researchers didn’t just measure how long the mice lived; they also conducted an exhaustive analysis of their health throughout their lives. They examined everything from body composition and metabolic rates to immune system function and cognitive abilities. This comprehensive approach allowed them to paint a detailed picture of how dietary restriction affects not just lifespan, but overall health and aging.
One of the most surprising findings was that many of the health benefits typically associated with dietary restriction, such as improved glucose metabolism and reduced body fat, didn’t necessarily translate into a longer life. In fact, some mice on restricted diets lived longer despite showing less improvement in these typical health markers.
“Our study really points to the importance of resilience,” says Gary Churchill, Karl Gunnar Johansson Chair and professor at JAX who led the study, in a statement. “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. It also suggests that a more moderate level of calorie restriction might be the way to balance long-term health and lifespan.”
This discovery challenges the long-held belief that calorie restriction extends life primarily by counteracting the negative effects of obesity. Instead, it suggests that dietary restriction might work through more complex mechanisms that we don’t yet fully understand.
The study also highlights the importance of genetics in determining lifespan. While diet played a significant role, genetic background explained nearly a quarter of the variation in lifespan among the mice.
Interestingly, the researchers identified several unexpected predictors of longevity. For example, mice that maintained their body weight during periods of stress tended to live longer, as did those with higher proportions of certain types of immune cells in their blood.
However, the study also demonstrates the potential downsides to extreme dietary restriction. Mice on the 40% calorie-restricted diet, while living the longest on average, also experienced significant loss of lean body mass and changes in their immune systems that could potentially make them more susceptible to infections.
“While caloric restriction is generally good for lifespan, our data show that losing weight on caloric restriction is actually bad for lifespan,” says Churchill. “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.”
Moreover, the research highlights the need for a more nuanced understanding of what constitutes “healthy aging.” Simply looking at traditional health markers like body weight or blood sugar levels may not tell the whole story when it comes to predicting longevity.
Moving forward, the study challenges us to rethink our approach to diet and aging. Instead of focusing solely on weight loss or metabolic markers, we may need to consider how to foster bodily resilience in the face of dietary changes. The key to a longer life might just be in our ability to adapt.
Paper Summary
Methodology
The study involved 937 female mice from a genetically diverse population. These mice were randomly assigned to five different dietary groups: unrestricted feeding, 20% calorie restriction, 40% calorie restriction, one day of fasting per week, or two consecutive days of fasting per week. The dietary interventions began when the mice were 6 months old and continued for their entire lives. Throughout the study, researchers conducted extensive health assessments, including measurements of body composition, metabolic rate, immune function, and various other physiological parameters.
Key Results
The study found that both calorie restriction and intermittent fasting extended the lifespan of mice, with effects proportional to the degree of restriction. Mice on 40% calorie restriction lived the longest, with a median lifespan about 9 months longer than unrestricted mice. Intermittent fasting also extended lifespan, even when overall calorie intake was similar to unrestricted mice. The research also revealed that many traditional health markers, such as reduced body fat or improved glucose metabolism, were not strongly associated with increased lifespan within dietary groups.
Study Limitations
The study was conducted only on female mice, so the results may not be directly applicable to males or to humans. Additionally, the extreme calorie restriction (40%) that produced the greatest lifespan extension also had potential negative effects, such as loss of lean mass and changes in immune function, which might be problematic in real-world applications.
Discussion & Takeaways
The research challenges some common assumptions about the relationship between diet, health, and longevity. It suggests that the life-extending effects of dietary restriction may be more complex than simply counteracting obesity. The study also highlights the importance of genetics in determining lifespan and the potential for personalized approaches to diet and aging. The findings on intermittent fasting are particularly intriguing, as they suggest a potentially more sustainable approach to gaining the benefits of dietary restriction.
Funding & Disclosures
The study was supported by Calico Life Sciences, a research and development company focused on aging and age-related diseases. Several of the study’s authors are employees of Calico Life Sciences, which could potentially be seen as a conflict of interest. However, the involvement of researchers from other institutions, including The Jackson Laboratory, adds credibility to the findings.
“Mice on 40% calorie restriction lived about nine months longer than those allowed to eat as much as they wanted. That’s equivalent to extending a human lifespan by over a decade!” Wrong! You cannot logically translate mouse-years into human-years. Unfortunately, these types of false equivalencies are made all the time in medicine.
More to this point: “The study also highlights the importance of genetics in determining lifespan. While diet played a significant role, genetic background explained nearly a quarter of the variation in lifespan among the mice.” If mice differ in response due to genetic differences, how on Earth can you extrapolate from mouse genetics to human genetics?
Bottom line: “This discovery challenges the long-held belief that calorie restriction extends life primarily by counteracting the negative effects of obesity. Instead, it suggests that dietary restriction might work through more complex mechanisms that we don’t yet fully understand.” And you won’t fully understand these mechanisms when you look at mice in a lab and not people on the street.
Animal studies are useless, cruel, and misleading. If you want to understand humans, then study humans. See my article, Stop Vivisection: Human Research for Human Disease. https://www.academia.edu/37390709/Stop_Vivisection_Human_Research_for_Human_Disease
Your story summary is incorrect. Your story says that the researchers found “that intermittent fasting can have similar effects, even without reducing overall calorie intake.” But the study found that “caloric restriction and intermittent fasting both resulted in lifespan extension *in proportion to the degree of restriction* . Fastng worked BECAUSE it imposed calorie restriction. No restriction, no life extension.