Intermittent fasting is so common that science has looked into how it affects the gut. They’ve found something alarming.

Unless you’ve been holed up in an underground bunker for an extended period of time, you’ve heard the term “intermittent fasting.” Between the diet’s proponents and its reactionaries (like any other diet), the truth is that it’s never been clear whether the proposal is healthy or beyond the reach of science. In other words, there has never been a long-term effort to find out the pros and cons. That’s exactly what happened, albeit with mixed results.

The popularity of intermittent fasting. We talked about this last year, it’s probably one of the dietary practices that has gained the most popularity in recent years. Basically, it’s a practice where the diet alternates between periods of eating and fasting. It doesn’t tell you what foods to eat, but when to eat them. It’s sort of a strategy used for weight management and metabolic health.

Is this recommended? Here’s the thing. A few weeks ago, we explained that calorie regulating in this way is not without risks and controversies. Previous research had found changes in the brain and gastrointestinal system, although the cause-and-effect relationships were unclear. More research was needed.

New research. An MIT study conducted on mice and published in the journal Nature analyzed how fasting can help the regeneration of intestinal stem cells. These cells are the source of new intestinal cells, and their regeneration can help the intestines. Although it found an increase in the regenerative capacity of intestinal stem cells, as we will see below, it also provided alarming news.

Experiment. The researchers built on a previous study in which they found that fasting can increase the regenerative capacity of intestinal stem cells.

What did they do? They focused on how this process works. To do this, they studied the intestinal stem cells of three different groups of mice: a control group that ate normally, one that fasted for 24 hours, and one that fasted and then was given the opportunity to eat for the next 24 hours.

Conclusions. The team noticed that the regeneration of these intestinal stem cells was actually suppressed during fasting, but then accelerated when the mice started eating again.

According to study researchers Omer Yilmaz, Shinya Imada and Sale, “The main finding of our current study is that refeeding after fasting is a distinct state from fasting itself. Refeeding after fasting increases the ability of stem cells to, for example, repair the gut after injury.

Bad news. We mentioned this at the beginning, but unfortunately the study didn’t just provide encouraging news for dieters. While increased regeneration may allow intestinal cells to heal faster, they also found that in the wrong circumstances, it can come at a cost.

How? Apparently, when they induced cancer-associated mutations in these stem cells during the refeeding phase, these cells were more likely to develop precancerous polyps, much more often than during the fasting phase.

Tumor risk. The study concludes that if cancer mutations occur during this regenerative phase, the mice have a higher risk of developing early-stage intestinal tumors. “High stem cell activity is good for regeneration, but too much of this beneficial substance over time may have less beneficial effects,” emphasizes Ömer Yılmaz.

More tests. As with any experimental and groundbreaking study, more testing will be needed to understand the full results. Also, the real effects of fasting in humans should be more complex than what we see in lab mice. So future experiments that look at the same changes will be able to test both the good and bad properties of human intestinal stem cells before and after fasting.

“Because biological pathways are highly complex and interconnected, the main message of our current study is that rigorous studies are needed to test the impact of any dietary intervention in humans,” they remind us in the study.

It’s better to understand the diet. Finally, the work shows that fasted mice produce lots of polyamines, which are organic compounds that play roles in things like helping cells grow, divide, and become other cells.

This is important because the next step will be to test whether polyamines can be used to easily mimic fasting in future studies, but they hope that the work will help them make the most of fasting.

“A careful analysis of the contribution of each phase of fasting (fasting versus refeeding after fasting) will give us a deeper understanding of how to design such dietary interventions to maximize regeneration while avoiding increased risk of other diseases such as cancer,” they say.

Image | Angie, RawPixel

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