A recent study found that if you put a lab mouse on a diet, cutting the animal’s caloric intake by 30 to 40 percent, it will live, on average, about 30 percent longer. Could this principle apply to human beings? Can we significantly extend our lives by eating less?
The concept of eating less to extend lifespan has been a subject of scientific interest at least since the 1930’s and today’s fad of intermittent fasting is based on that principle.
Studies done on various species from worms to rodents, have shown that calorie restriction, which involves reducing daily calorie intake without malnutrition, may have a significant impact on longevity. This is thought to be due to a decrease in metabolic rate and a reduction in the accumulation of cellular damage over time.
Human studies, although more complex due to ethical and practical considerations, have also indicated potential benefits. For instance, a study published in Nature Aging found that a two-year intervention requiring participants to cut 25 percent of their daily calories slowed the pace of aging. Similarly, research from the 1930s observed that reducing the normal food intake of mice by about 40% increased their maximum lifespan by 30% to 40%. These findings suggest that calorie restriction could influence biological processes related to aging and disease. But the overall picture is much more complex than that, with a lot of twists and turns in the conclusions drawn.
The idea is that by eating less, the body may enter a state of mild stress, which activates certain pathways that improve cellular repair processes and reduce inflammation. This state, often referred to as hormesis, could theoretically slow down the aging process. However, it’s important to note that calorie restriction should not lead to malnutrition, and the approach must be carefully managed to ensure all nutritional needs are met.
Calorie restriction also forces the body to rely on fuel sources other than glucose, which aging experts think is beneficial for metabolic health and, ultimately, longevity. Several researchers pointed to a process known as autophagy, where the body eats up malfunctioning parts of cells and uses them for energy. This helps cells function better and lowers the risk of several age-related diseases.
In fact, scientists think that one of the main reasons calorie-restricted diets make mice live longer is because the animals don’t get sick as early, if at all, said Dr. Richard Miller, a professor of pathology at the University of Michigan.
Not all the studies in the field yielded positive results. Most striking was a study by Dr. Richard Nelson, a professor of pathology at the University of Michigan, published in 2010 on mice that were genetically diverse. He found that some of the mice lived longer when they ate less, but a larger percentage actually had a shorter life span.
“That was kind of really unheard of,” Dr. Nelson said, noting that most papers on calorie restriction start out by saying: “‘Food restriction is the most robust, almost universal means of extending life span in species across the animal kingdom’ and blah, blah, blah.”
Other researchers have studied the patterns of food accessibility, a principle that today has translated into the popular fad of “intermittent fasting.” That result too proved to be inconclusive; it’s difficult to determine whether intermittent fasting, calorie restriction or a combination of the two could cause people to live longer.
“I don’t think we have any evidence that it extends life span 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.”
Dr. Kim Huffman from the Duke University Medical School, added a final surprising twist to the theories being considered, explaining that indeed, there is also a considerable body of evidence that appears to directly contradict the idea that calorie restriction extends the human life span.
Research consistently finds that people who are classified as overweight have a lower risk of death than those who are normal or underweight. One hypothesis is that people with the lowest B.M.I.s may be thin because they are older or have a chronic illness. Another is that people with higher B.M.I.s have more muscle, which weighs more than fat. But it’s also conceivable Dr. Huffman said that, especially later in life, having greater body mass is actually protective.
After much research and countless studies, the verdict is still out on whether calorie restriction and today’s fad of intermittent fasting can help you live longer.
