Caloric Restriction: Key to Better Health, Longer Life?

A long-awaited study has found that limiting caloric intake not only preserves health but also increases longevity. The paper, which was published in Nature Communications, involved decades of study of rhesus monkeys, is said to resolve the debate over whether caloric restriction (CR) extends lifespan. 1, 2,3

caloric restriction

“The main message from this study is that the amount you eat influences how you age,” said Rozalyn Anderson, study author and associate professor, Department of Medicine, University of Wisconsin-Madison. “The work shows that in primates, reducing calorie intake in adulthood and later in life confers benefits in terms of both health and survival.” 1, 4

The latest findings represent the collaboration between two competing research teams—one at the University of Wisconsin-Madison (UW) and the other at the National Institute on Aging (NIA)—that worked together in an effort to explain their differing observations on the impact of CR on longevity.  1, 2, 3

Both teams had initially set out to study the effects of caloric restriction--defined as a diet comprised of about 30% fewer calories but providing the same nutrients as a standard diet—on rhesus monkeys, who as they age are vulnerable to many of the same diseases as humans. 1, 2, 3

In 2009, the UW research team reported significant extension of life and reductions in cardiovascular disease, cancer and insulin resistance in the monkeys whose diets were calorically restricted. But in 2012, while the NIA group also found better health among its CR monkeys, the researchers observed no significant improvement in survival. 1, 2, 3

The conflicting findings cast doubt on the benefits of CR on longevity and appeared to go against nearly a century of laboratory research showing that CR significantly extends lifespan, albeit in non-primates. Beginning in the 1930s, for example, researchers found that laboratory rats and mice live up to 40% longer when fed a diet that has at least 30% fewer calories than they would normally consume. Substantial research over the last two decades has also demonstrated the benefits of CR in short-lived organisms such as yeast, nematodes and fruit flies. 1, 2, 3, 5

But, after sifting through all the information from the two study sites including data from nearly 200 monkeys, the authors concluded that CR is indeed associated with longer survival. The observed discrepancies, they said, stemmed from a variety of factors including: diet composition (the NIA monkeys ate naturally-sourced foods while the UW group ate relatively more processed foods with higher sugar content); the age of the monkeys when the restricted diets were introduced (eating less confers benefits in adult primates but not in younger animals—which, by the way, is unlike in rodents, where the earlier the animals begin CR the longer the resulting lifespan); and genetics. 1, 2, 3

Any Benefits for Humans?

Of course, the research begs the question of what all this means for humans. The study authors say their findings suggest that CR mechanisms are likely translatable to human health. “The profound similarities between humans and rhesus monkey in the rate of aging, the types of diseases of aging that occur, and how they manifest clinically makes it extremely likely that the mechanisms of CR in monkeys will be translatable to human health and aging too.” Anderson said. 1, 4

It appears that researchers who have looked at CR in humans agree. “There are numerous examples from well-studied human cohorts that there is a likely benefit for reduced-calorie diets to promote healthy aging and lifespan extension in humans,” said Leanne Redman, Ph.D, associate professor and investigator in the CALERIE study at the Pennington Biomedical Research Center at Louisiana State University in Baton Rouge. “As humans strive for the fountain of youth in today's obesogenic environment, looking to dietary and nutritional approaches for improved health across the lifespan is the most obvious choice.” 6, 7

Indeed, one theory is that CR evolved as a protective response to enable animals—and humans—to survive periods of food shortage. But this evolutionary advantage might seem to backfire in today’s environment of overabundant and chronic accessibility to food combined with a trend of reduced physical activity. 6

Others see in the latest research the value of diet composition. “The more wholesome and less-refined diet consumed by the NIA monkeys—which contained substantially less sucrose, more favorable lipid and protein sources and higher fiber relative to the Wisconsin diet—appears to have benefits independent of the level of CR,” said Susan B. Racette, Ph.D., professor at Washington University School of Medicine in St. Louis. “This finding is encouraging for human application, given the challenges of adhering to a calorically-restricted diet long-term.” 8, 9

 

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