Fasting may lead to a longer life. However, not everyone can benefit equally from these effects, new research suggests.
For nearly a century, animal studies across numerous species have demonstrated a link between calorie restricted diets and longevity. However, such dietary patterns pose a range of challenges when it comes to interpreting these results for humans, especially when it comes to compliance, eating disorders, and overall physical health.
Intermittent fasting—an alternative form of dietary restriction which involves calorie restriction—has been put forward as a potentially more sustainable and practical eating pattern for humans. However, while it has been demonstrated as an effective method for weight loss, its efficacy in life span extension has been largely unexplored.
In a new study, published in the journal Nature, researchers from Calico Life Sciences, the Jackson Laboratory and the University of Pennsylvania investigated nearly 1,000 genetically diverse mice to compare the impacts of calorie restriction and intermittent fasting on overall health and survival.
"Our goals for this study were to address the basic biology of aging and to understand how genetically diverse mice (more like people than standard inbred lab mice) would respond to life extending interventions," Gary Churchill and Andrea Di Francesco, the senior and lead authors on the study, respectively, told Newsweek.
The mice were randomly assigned one of five diets: unlimited access to food; fasting one day per week; fasting two consecutive days per week; calorie restriction of 20 percent of baseline food intake; and calorie restriction of 40 percent.
All dietary restriction was associated with an extended life span in the mice, with responses being proportional to the degree of restriction. But the devil is really in the detail.
"The mice on restricted diets did have on average longer life span and they were generally healthy, but there were also indications of detrimental effects—lower body temperature, food seeking behavior, and changes to blood and immune system that suggest they would be susceptible to infections," Churchill and Di Francesco said.
However, these improvements were not consistent across all animals, and while dietary restriction was associated with numerous beneficial health effects, genetics had a much larger influence—roughly three times as big—on life span than dietary intervention.
The researchers also noted that while dietary restriction was associated with an improvement in various metabolic traits, such as blood glucose levels and body fat, these improvements did not appear to be directly associated with life span extension.
"[These metabolic improvements are] a good thing whether or not it moves the needle on aging," Churchill and Di Francesco said. "In modern societies, metabolic diseases are a serious health concern."
So, what does this mean for us?
"The dietary interventions used with mice in this study would not be tolerated by people," Churchill and Di Francesco said. "Even the milder one day fasting or 20 percent restriction, when translated to human equivalents, are not practical for long-term in people."
More research is needed to confirm whether any sort of dietary restriction could convey life-extending benefits in humans, but these findings demonstrate an important level of nuance in the conversation surrounding food intake and longevity.
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Reference
Di Francesco, A., Deighan, A. G., Litichevskiy, L., Chen, Z., Luciano, A., Robinson, L., Garland, G., Donato, H., Vincent, M., Schott, W., Wright, K. M., Raj, A., Prateek, G. V., Mullis, M., Hill, W. G., Zeidel, M. L., Peters, L. L., Harding, F., Botstein, D., Korstanje, R., Thaiss, C. A., Freund, A., & Churchill, G. A. (2024). Dietary restriction impacts health and life span of genetically diverse mice. Nature. http://dx.doi.org/10.1038/s41586-024-08026-3
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