Food proposals that lead to rapid reduction of overweight are called “yo-yo diets”, but then produce weight gain. They are “cyclical changes in weight”, and it is a pattern that consists of losing weight and then getting fat again. However, more and more scientific research finds evidence about the risks of harm that restrictive diets have for human health.
There are now indications that body weight fluctuations resulting from dramatically reducing and increasing calories could cause physiological changes that increase the risk of heart disease, such as heart attacks, or diabetes later in life.
The term “yo-yo diet” was coined by Kelly Brownell of Yale University. It refers to the cyclical movement of the rise and descent of the famous toy. In this process, the person who goes on the diet is initially successful in losing weight, but does not manage to maintain those kilos in the long term. Start gaining weight again. The person tries to lose the recovered weight, and the cycle starts again.
The new evidence comes from a new study conducted on mice. It was presented at the annual meeting of the American Society of Physiology during the 2022 Experimental Biology (EB) meeting, held in Philadelphia from April 2-5. It offered possible perspectives on the long-term impact of weight loss diets, as well as on involuntary reductions in food intake caused by food insecurity.
Most of the previous analyses in humans and animals have focused on the short-term impacts of weight loss. But researchers say that less is known about how weight loss and gain cycles can affect health in the long run.
For the study, the researchers divided 16 mice into two groups. One group received a normal amount of food throughout the study, while the other group experienced three cycles of a restricted diet (60% of their normal daily food intake), followed by three weeks of a normal diet.
At the end of the study, the researchers used ultrasound resonance technology to assess the cardiac and renal functioning of mice. They also did blood tests to assess insulin sensitivity, a measure of how the body processes sugar.
“We found that animals that went through several cycles of weight loss and body weight recovery had reduced heart and kidney function in the end. They also had more insulin resistance, which may be a cause of diabetes,” says Dr. Aline M. A. de Souza, a postdoctoral fellow at Georgetown University in Washington, DC, who was the first author of the study. “Although animals appear to be healthy after 'recovery' from their diet, their heart and metabolism are not healthy,” he warned.
Their findings also raise questions about public health in light of the COVID-19 pandemic, such as whether people who had problems accessing food as a result of the pandemic's closures and economic impacts face a higher incidence of cardiovascular problems in the coming years.
“Our data supports the need for additional research on people to find out whether individuals who cycle heavily restrictive diets to lose weight are at greater risk of developing heart problems later,” de Souza said.
“We still need to do more studies in this field, but the results suggest that the more restrictive the diet, the worse the health outcomes can be. Slimming diets must take into account long-term health, especially if rapid weight loss is considered as an option,” he said.
While more research is needed to determine the biological mechanisms underlying the findings and to determine whether patterns observed in mice carry over to humans, researchers speculate that changes in gene expression in response to caloric restriction could alter the biological pathways they regulate blood pressure and insulin metabolism.
In Argentina, Dr. Mónica Katz, former president of the Argentine Nutrition Society, promoted the movement against diets that can affect health. “Diets that are restrictive, forbid food or that reduce calories should not be followed, because scientific research has shown that the human brain begins to identify that it does not have enough food and causes the feeling of hunger. Dieting also involves depriving yourself of pleasure. After a few months, the person eats a lot again, and becomes more overweight,” Katz explained.
On the other hand, gradually losing weight is beneficial. One of the reasons for making changes that involve only a progressive decrease in weight is how the human organism is composed, according to Katz, who is the author from the book No Diet. Every kilo of weight lost is composed, on average, of 75% fat and 25% of muscle, water and bone. That composition is maintained as long as you do not thin out too quickly. If you go on a fast diet, not only does the quality of the lost weight change — 50% fat and 50% lean mass or water — but the regain of kilos will be in the form of fat.
For the specialist, every person who wants to lose overweight has to create a safe environment: not to have at hand the products triggering uncontrolled, to avoid snacking or a large portion. You should have 4 meals a day at flexible times. Eat only one dish at each meal, and “consume meat, fish or chicken once a day plus vegetables or legumes as a side dish and in the other main meal some cereal, some good quality pasta, added to vegetables. You can eat sweets, but in small portions.” He also suggested that we must learn to manage daily stress without eating food.
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