What are the possible health benefits (and risks) of fasting?

He intermittent fasting It is a method of restricting foods for a certain period of time and has become very popular among those looking to lose weight in recent years.

It has been shown in several studies that this diet can have positive effects on health, such as delaying the onset of certain diseases and prolonging life.

But beyond these benefits, the biological mechanisms behind these benefits remain largely unknown.

A few years ago, researchers at the Massachusetts Institute of Technology (MIT) in the United States suggested that one of the beneficial effects of intermittent fasting is to stimulate regenerative capacity of intestinal stem cells . This helps the intestine recover from inflammation or other damage.

In a new study conducted on mice and published on August 21 in the Nature Review Scientists have managed to discover the pathway that allows this regeneration, which is activated once the rodents resume their diet after the diet. Also It has been found that increased intestinal stem cell activity is not free, as it can lead to health risks.

“Having more stem cell activity is good for regeneration, but too much of a good thing over time can have less favorable consequences.” Ömer Yilmaz, associate professor of biology at MIT and lead author of the study, detailed in a statement.

For years, the team led by Yilmaz has been trying to understand How fasting and low-calorie diets can impact gut health.

In research conducted in 2018, researchers discovered that during fasting, intestinal stem cells can use lipids as an energy source instead of carbohydrates. In addition to this, they were able to demonstrate that this practice promotes an increase in the regenerative capacity of stem cells.

But they still needed to figure out how fasting causes this increase in stem cell activity and when it occurs.

“Is it the fasting itself that causes regeneration or is it the post-fasting diet?” asked the MIT professor and his colleagues.

To answer these questions, the team led by Yilmaz studied three groups of mice: one that fasted for 24 hours, another that fasted for 24 hours and then was allowed to eat again for a day, and finally, one that was allowed to eat whenever they wanted, such as during the investigation.

Once the experiment was completed, the next step was study the proliferation capacity of intestinal stem cells rodents at different times.

There, they found that stem cells multiplied at a much faster rate in the group of mice that had fasted for a full day and then been allowed to feed again for the same period.

Proliferation was much greater at the end of the 24-hour refeeding period, when the rodents had already had a chance to eat. This is why the study suggests that breaking the fast is more beneficial for health than fasting itself.

“We think that fasting and refeeding represent two different states,” explained Shinya Imada, a postdoctoral researcher at MIT and another author of the study.

“During fasting, the ability of cells to use lipids and fatty acids as an energy source allows them to survive when nutrients are low. And then it’s the post-fasting refeeding state that really drives regeneration. When nutrients are available, these stem cells and progenitor cells activate programs that allow them to generate cell mass and repopulate the intestinal mucosa,” Imada added.

Research has identified that intestinal stem cells are able to activate a cell signaling pathway known as mTOR which has been linked to cell growth and metabolism. When this is activated, cells are able to generate more proteins, and through this protein synthesis, stem cells can increase.

The recent Nature study also revealed that there is a downside to the highly regenerative state. And when stem cells are in a highly activated regeneration process, they are more likely to become cancerous.

This is because intestinal stem cells are among the most frequently dividing cells in the body, allowing the lining of the intestine to renew itself every five to ten days.

According to the findings, By activating a cancer-causing gene in mice during this refeeding period, the animals were more likely to develop tumors than when the gene was activated during fasting.

Additionally, cancer-related mutations during the refeeding process were more likely to generate polyps than mutations that occurred in other groups of mice. Polyps are small masses that develop in the tissues of the lining of a hollow space, in this case the intestine.

“Given these findings, fasting-refeeding cycles should be carefully considered and tested when planning diet-based regeneration strategies without increasing cancer risk, because refeeding after fasting results in a sudden increase in stem cell-mediated regeneration and tumorigenicity,” the study concludes.

Yilmaz, for his part, stressed that his experiment used mice and “very defined cancer mutations” and that in the case of humans, “it will be a more complex state.”

Despite this, the researcher explains, his findings lead to the following notion: “Fasting is very healthy, but if you’re unlucky and you refeed after a fast and you expose yourself to a mutagen, like a charred steak or something, you could actually increase your risk of developing an injury that could lead to cancer.” .

Other scientists who weren’t involved in the study, such as Valter Longo, a biogerontologist at the University of Southern California in Los Angeles, have reservations. As the scientist explained to Nature , the mice with the altered genes were “almost doomed to cancer,” and the increased risk found in the research may not apply “more broadly.”

Longo recalled a 2015 study that identified a 45% decrease in abnormal cell and tissue growth in fasted rodents, compared with other specimens that had not undergone dietary restriction.

The MIT team plans to conduct a clinical trial in the future to clarify whether the results of the recent study apply to humans.