If you put a person on a diet Laboratory mouseBy reducing your caloric intake by 30 to 40 percent, you will live, on average, 30 percent longer. The calorie restrictionas the intervention is technically called, cannot be so extreme that the animal becomes malnourished, but it must 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 reproduced in species ranging from worms until the monkeys. Later studies also found that many of the animals with calorie restriction were less likely to develop cancer and other chronic diseases related to aging.
But despite all the animal research, there are still many unknowns. Experts continue to debate how it works and whether the number of calories consumed or the time interval in which they are ingested (also known as intermittent fasting).
And it also remains frustratingly uncertain to know if eating less can help you live longer. The aging experts are famous for experimenting with different dietary regimens on themselves, but studies on longevity are scarce and difficult to carry out because, well, they take a long time.
Here’s what scientists have learned so far, mostly through groundbreaking animal studies, and what they think it could mean for humans.
Scientists don’t know exactly why eating less would make an animal or person live longer, but many hypotheses have an evolutionary bias. In nature, animals experience periods of abundance and shortage, just like our human ancestors. Therefore, your biology (and possibly our own) evolved to survive and thrive not only during times of plenty, but also during times of deprivation.
A theory is that, at the cellular level, the calorie restriction makes them animals are more resistant to physical stress factors.
For example, the mice with calorie restriction are more resistant to toxins and recover faster from injuries, he explained James Nelsonprofessor of Cellular and Integrative Physiology at the Health Sciences Center of the University of Texas at San Antonio.
Other explanation includes the fact that, in both humans and animals, ingesting less calciumOrias slows down metabolism. It is possible that “the less you have to metabolize the body, the longer you can live“, he claimed Kim Huffmanassociate professor of medicine at Duke University School of Medicine, who has studied calorie restriction in people. “You know, slow down a little and the tires will last longer,” she exemplified.
Caloric restriction also forces the body to resort to different fuel sources of the glucosewhat the aging experts considered beneficial for metabolic health and, ultimately, for longevity. Several researchers pointed to a process known as autophagy, in which the body eats the malfunctioning parts of cells and uses them as a source of energy. This helps cells function better and reduces the risk of several age-related diseases.
In fact, scientists believe that one of the main reasons low-calorie diets make mice live longer is that the animals don’t get sick as soon, if at all, he explained. Richard MillerProfessor of pathology of the University of Michigan. There are some notable exceptions to the findings on longevity and calorie restriction.
The most striking thing was a study that Nelson published in 2010 on genetically diverse mice. He discovered that some of the mice they lived longer when they ate lessbut a larger percentage actually had a shorter life. “That was really unheard of,” he said. Nelsonpointing out that most articles on calorie restriction begin by saying, “’Food restriction is the most robust and nearly universal means of prolonging life in species throughout the animal kingdom’ and blah, blah, blah.”
Others researchers have disputed the importance of the findings of Nelson. “People cite this study as if it were blanket proof that calorie restriction it only works a little bit, or part of the time,” Miller said. “But you can only come to that conclusion if you ignore 50 years of solid published evidence that says it works almost all the time.” However, Nelson’s study was not the only one that did not find a universal benefit for longevity with the calorie restriction. For example, two studies conducted in monkeys over more than 20 years, published in 2009 and 2012, reported conflicting findings.
The animals in both experiments showed some health benefits related to calorie restrictionbut only one group lived longer and had lower rates of age-related illnesses, such as cardiovascular and diabetes.
How much influence does intermittent fasting for longevity?
Given these disparate results, some researchers wonder if there may be another variable at play that is as or more important than the number of calories an animal ingests: the time interval in which it ingests them. A key difference between the two monkey trials was that in the 2009 study, conducted at the University of Wisconsinthe calorie-restricted animals only received one meal a day and the researchers removed the leftover food in the late afternoon, so the animals were forced to fast for about 16 hours.
In the 2012 study, led by National Institute on Aging (NIA)the animals were fed twice a day and food was left out overnight. The Wisconsin monkeys lived the longest.
A more recent study in mice explicitly tested the effects of calorie restriction with and without intermittent fasting. The scientists gave the animals the same low-calorie diet, but some had access to the food for just two hours, others for 12 hours and another group for 24. Compared to a control group of mice that could be fed at any time On a full-calorie diet, low-calorie mice with 24-hour access lived 10 percent longer, while low-calorie mice that ate within specific time intervals had up to 35 percent longer lifespans. .
Based on these findings, Rafael de Cabo, a senior NIA researcher who helped lead the monkey study, now believes that while calorie restriction is important for longevity, the amount of time spent eating – and not eat – every day is just as decisive. And it could be the case not only for animals, but also for humans.
What does this mean to me?
It is difficult to answer definitively whether the intermittent fastingthe calorie restriction or a combination of both can make people live longer. “I don’t think we have evidence that it prolongs the life of human beings,” he said. Nelson. That doesn’t mean it can’t work, he added, just that the tests are “very hard to get because it takes a lifetime to get that data.”
A clinical trial — called a study Calerie–tried to answer this question by examining how the reduction of calories by 25 percent over two years affected a series of measures related to aging. More than 100 healthy adults were counseled on meal planning and offered regular advice to help them achieve their dietary goals.
But since it is so difficult to reduce the calories, in the end the participants were only able to reduce their intake by 11 percent. Compared to control participants, people on diet improved several aspects of their health cardiometabolicas the blood pressure and the insulin sensitivityand presented lower levels of some inflammation markers. The study also included three measures of “biological age,” comparing analyzes of blood carried out at the beginning and at the end of the two years.
Two of the tests showed no improvement in either group, but the third, which aims to measure how quickly people age, did show a difference in people on diet. The calorie restriction “it did not rejuvenate people, but it did slow down their rate of aging“, he claimed Huffmanwho worked on the trial.
For Millerthe most significant conclusion of this study is that the calorie restriction 25 to 40 percent that has been shown to be beneficial in animals It is not realistic in people. “Everything possible was done to help them” reduce the calorieshe said, and they still fell short of the 25 percent goal. From Cape had a different opinion: “With only 11 percent of calorie restriction that the participants achieved continue to show benefits,” he said. Others research have focused on the short-term effects of intermittent fasting in people with different body mass indexes.
Some studiesin which various fasting programs were tested, showed an improvement in metabolic health and a reduction in inflammation. But in a trial of 116 people whose body mass index classified them as obese or with overweight No benefit was seen among those who ate within an eight-hour interval but did not reduce their caloriescompared to a control group.
And to add a final touch, there is a remarkable body of evidence that seems to directly contradict the idea that calorie restriction or the fastwhich usually leads to weightloss, extends human life. Research consistently concludes that people with overweight have a lower risk of dying than those with a weight normal or less than normal.
One hypothesis is that people with BMI (Body Mass Index) shorter ones may be thin because they are older or have a chronic disease. Another is that people with BMI taller people have more musclewhich weighs more than fat. But it is also conceivable that, especially at older ages, having a greater body mass be really protective, he said Huffman.
Despite almost a century of research, there is still a long way to go before experts can state with certainty whether the longevity benefits observed in animals will move to the Humans.
Some studies give reason to believe that calorie restriction and the intermittent fasting will help you live longer, and there are likely to be short-term benefits, especially when it comes to cardiac and metabolic health. But it’s also possible that eating less won’t do much more than leave you hungry.
©The New York Times 2024
