In recent years, scientific health research has focused on finding a link between caloric restriction and increased lifespan in humans. Scientists are also trying to find a link between intermittent fasting and longevity.
If you put a laboratory mouse on a diet reducing the animal’s caloric intake by 30-40%, it will live, on average, about 30% longer, according to an article in The New York Times.
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Caloric restriction, as the intervention is technically called, cannot be so extreme that the animal is malnourished, but it should be aggressive enough to trigger some key biological changes.
Scientists first discovered this phenomenon in the 1930s, and over the past 90 years it has been replicated in species from worms to monkeys.
Calorie-restricted animals were less likely to develop cancer
Subsequent studies also found that many of the calorie-restricted animals were less likely to develop cancer and other chronic diseases related to aging.
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But despite all the animal research, much remains unknown. Experts still debate how it works and whether the number of calories consumed or the window of time in which they are consumed (also known as intermittent fasting) matters more.
Whether eating less can help people live longer is still uncertain. Aging experts are famous for experimenting with different diets themselves, but actual longevity studies are few and far between and difficult to do because they take a long time.
Why would cutting calories increase longevity?
Scientists don’t know exactly why eating less would cause an animal or person to live longer, but many hypotheses have an evolutionary bent. In the wild, animals go through periods of feast and famine, just like our human ancestors.
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Therefore, their biology (and perhaps ours) has evolved to survive and thrive not only during seasons of abundance, but also seasons of scarcity.
One theory is that, at the cellular level, caloric restriction makes animals more resistant to physical stressors.
For example, calorie-restricted mice have greater resistance to toxins and recover faster from injury, said James Nelson, a professor of cellular and integrative physiology at the University of Texas at San Antonio.
Eating fewer calories slows down your metabolism
Another explanation involves the fact that, in both humans and animals, eating fewer calories slows metabolism.
“The less you have to make your body metabolize, the longer it can live,” said Dr. Kim Huffman, an associate professor of medicine at Duke University School of Medicine, who has studied caloric restriction in humans.
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Caloric restriction also forces the body to rely on fuel sources other than glucose, which aging experts believe is beneficial for metabolic health and ultimately longevity.
There are also studies that dispute the link between caloric restriction and longevity
There are some notable exceptions to the findings around longevity and caloric restriction. The most striking was a study published by Dr. Nelson in 2010 on mice that were genetically different.
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He found that some of the mice lived longer when they ate less, but a higher percentage actually had a shorter lifespan.
What does intermittent fasting have to do with this?
In the face of these conflicting results, some researchers wonder if there might be another variable at play that is as important or even more important than the number of calories an animal consumes: the time window in which they consume them.
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A key difference between the two monkey studies was that in the 2009 study at the University of Wisconsin, the calorie-restricted animals were given only one meal per day, and the researchers ate any leftover food at the end of the afternoon. so the animals were forced to fast for about 16 hours.
In the 2012 study by the National Institute on Aging, animals were fed twice a day and the food was left out overnight. The monkeys from Wisconsin were the ones that lived the longest.
Although caloric restriction is important, the amount of time spent eating and not eating is critical
A more recent study in mice explicitly tested the effects of caloric restriction with and without intermittent fasting. The scientists gave the animals the same low-calorie diet, but some had access to food for only two hours, others for 12 hours, and another group for 24 hours.
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Compared to a control group of mice that could binge on an all-calorie diet at any time, the low-calorie mice with 24-hour access lived 10 percent longer, while the mice low-calorie dieters who ate at certain intervals had up to a 35% increase in lifespan.
While caloric restriction is important for longevity, the amount of time spent eating and not eating each day is just as critical.
How can the findings of the studies be applied to humans?
“I don’t think we have any evidence that it extends life in humans,” Dr. Nelson said. That doesn’t mean it can’t work, he added, just that the evidence is “very hard to come by because it takes a lifetime to get that data.”
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A clinical trial – called the Calerie study – attempted to answer this question by examining how cutting calories by 25% for two years affected a number of measures related to aging.
More than 100 healthy adults were counseled on meal planning and received regular counseling sessions to help them meet their dietary goals. But because it’s so difficult to cut calories, the participants were ultimately only able to reduce their intake by about 11 percent.
Compared to control participants, dieters improved several aspects of their cardio-metabolic health, including blood pressure and insulin sensitivity, and had lower levels of several markers of inflammation.
Calorie restriction doesn’t make you younger, but it does make you age more slowly
Calorie restriction “didn’t make people younger, but it made the rate at which they aged slower,” said Dr. Huffman, who worked on the study.
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Despite nearly a century of research, there is still a long way to go before experts can say with certainty whether the longevity benefits seen in animals will transfer to humans.
Some studies offer reason to believe that caloric restriction and intermittent fasting will help you live longer, and there are likely shorter-term benefits, especially when it comes to heart and metabolic health. But it’s also possible that eating less will do little more than make you hungrier.
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