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Public interest in diets that supposedly extend our lifespan remains high, but scientists caution that research on these diets in people is limited. d3sign/Getty Images
  • Many anti-aging diets are being promoted as ways to extend your lifespan.
  • However, much of the research on anti-aging diets has been done in animals — not humans.
  • Researchers caution that data on the benefits of these diets for people is limited.
  • Speak with your doctor before you begin any new diet to make sure it’s a healthy choice for you.

For years, certain foods have been promoted as the key to a long and healthy life, from common vegetables and “healthy” fats to powders made from exotic plants.

But a number of anti-aging diets focus not on what you should eat, but instead on limiting your intake of food overall or restricting your meals to certain days or times of the day.

These diets include calorie restriction, intermittent fasting, fasting-mimicking diet, the keto diet, and time-restricted feeding.

All of these are intended to not only increase your life, but also extend the number of years you’re in good health, known as lifespan and healthspan, respectively.

Much of the research on anti-aging diets has been done in non-human organisms — from microbes to worms to rodents.

One reason for this is that it’s easier to follow the entire lifespan of these creatures, because their lives are so much shorter.

Research in people is also starting to suggest that some dietary patterns may help people live longer and age more gracefully.

However, some researchers caution that data on the benefits of these diets for people is limited — especially when it comes to knowing if eating a certain way can extend the human lifespan.

“Despite their recent popularization, there is not yet strong evidence that any of the anti-aging diets studied in laboratory animals have substantial long-term health benefits in non-obese humans,” wrote Matt Kaeberlein, PhD, and his colleagues in a review in the journal Science.

In the Science paper, Kaeberlein and his colleagues reviewed existing research on anti-aging diets, focusing on studies done in rodents, and whenever possible, people.

In the rodent studies, the most promising anti-aging diets involved calorie restriction.

This included the “classic” calorie restriction diet, where daily calories are reduced by 20 to 50 percent, and a variation that involves reducing overall calories but maintaining protein intake.

This fits with other research looking at the opposite — the impact of greater food intake.

Michael J. Forster, PhD, a researcher at the University of North Texas Health Science Center who studies aging, said research shows that when rodents and non-human primates consume more calories than their body uses, they see a reduction in life expectancy.

The size of this lifespan shortening depends on how much excess food is eaten and for how long, he said.

“One could argue from the rodent studies that the difference in life expectancy [between animals] due to caloric intake is up to 50 percent,” said Forster.

Another diet that Kaeberlein and his colleagues found promising is intermittent fasting, in which mice fasted for 1 day in between feedings.

However, this is also considered a type of calorie restriction because mice end up consuming fewer calories overall due to the fasting days.

Scientists have studied other diets, as well, but so far, calorie reduction seems to have the biggest impact on the lifespan of rodents and other non-human organisms.

“The evidence is poor that any current dietary practice other than [calorie restriction] will significantly and broadly influence health and longevity,” said Forster.

In spite of the promising results in rodents, so far no anti-aging diets have been shown to be effective in the clinic, wrote Kaeberlein and his colleagues.

“However, there is some evidence consistent with anti-aging effects for [calorie restriction] and related diets in humans,” they added.

Valter Longo, PhD, a researcher who studies aging at the University of Southern California Leonard Davis School of Gerontology, said part of the problem with this research is that researchers, scientists, and clinicians often work in isolation.

“What’s missing is a multi-disciplinary approach,” he said. “If you put all [the research] together, you get a very different picture — with certain nutritional interventions not only consistently associated with health, but also with longevity.”

Because of the challenges of following people for decades, much of the anti-aging diet research focuses on shorter-term benefits.

For example, caloric restriction over a period of 2 years has been found to improve insulin sensitivity and risk factors for cardiovascular disease.

The fasting-mimicking diet has also been found to improve body mass index (BMI), blood glucose levels, blood pressure, and other health markers.

While much of the emphasis of anti-aging diet research is on pushing the boundaries of lifespan and healthspan, Forster thinks researchers should focus more on why some people lose their physical and mental function as they age.

“What processes and preventable events contribute to failure to achieve optimal health during aging and make us vulnerable to disease?” he said.

Although more research on these diets is needed, “from one perspective, we already have significant information,” said Forster. “Maintaining a healthy weight throughout life tends to maximize health and longevity.”

Longo also thinks scientists have enough data on the benefits of less extreme diets to be able to recommend them to certain groups.

For example, while he doesn’t think people should do 16 hours of fasting every day for the rest of their lives, a shorter fast period during the day should be safe for most people.

“There are no studies that I’ve ever seen on 12 hours of fasting and 12 hours of feeding every day being harmful,” he said.

For other diets, such as the fasting-mimicking diet which Longo studies, there are more caveats. But not so many that Longo couldn’t easily rattle them off in 30 seconds.

Some of his warnings are against doing these diets too often or too extremely — or when there are medical reasons for a person to not restrict their diet.

“What if you restrict yourself too much or for too long? What if you restrict yourself when you’re 85? Well, that could be a big problem,” said Longo.

Severe calorie restriction can potentially lead to increased cold sensitivity, decreased sex drive, poor sleep, chronic fatigue, and muscle weakness.

A study by Longo and his colleagues also found that while a low protein diet was beneficial for people ages 50 to 65, those over 65 on this diet had a higher risk of dying.

Other researchers have raised a concern that intermittent fasting and other restrictive diets could lead to disordered eating.

While not everyone who restricts their eating to every other day or within an 8-hour window will go on to develop an eating disorder, some people may have a higher risk.

As for the fasting-mimicking diet, Longo said many people could benefit from doing this 2 or 3 times a year, but not more frequently.

But, he said there are other dietary patterns — not related to calorie restriction — that are known to be beneficial.

This includes eating a low protein diet (but not too low, especially if you’re an older adult), and eating a more plant-based diet, and if you’re vegan, ensuring that you get all the macronutrients you need, especially amino acids.

“While you have the need for personalization [of the diet],” said Longo, “there are some things that will benefit the great majority of people.”