Scientists Are Starting to Unravel How Fasting Affects the Gut

Fasting’s effects on our body might be more complicated than we thought. New research in mice suggests that fasting can speed up the healing of intestinal stem cells, but possibly make them more susceptible to becoming cancerous. The findings could help us optimize popular diets like intermittent fasting, the researchers say.

Scientists at MIT led the new research, published Wednesday in the journal Nature. In a previous study, they found that fasting can increase the regenerative ability of intestinal stem cells, but now they’ve zeroed in on how this process seems to work.

The researchers studied the gut stem cells of three different groups of mice: a control group that ate as usual, mice that were kept on a fast for 24 hours, and mice that were on a fast and then allowed to eat to their heart’s content for the next 24 hours. This time, they noticed that the regeneration of these intestinal stem cells was actually suppressed during the act of fasting itself, but would then ramp up once the mice began to eat again.

“The major finding of our current study is that refeeding after fasting is a distinct state from fasting itself. Post-fasting refeeding augments the ability of intestinal stem cells to, for example, repair the intestine after injury,” study researchers Omer Yilmaz, Shinya Imada, and Saleh Khawaled told Gizmodo in an email.

While this boost in regeneration might allow our gut cells to heal faster, the researchers also found that it could come with a price under the wrong circumstances. When the researchers induced cancer-linked mutations in these stem cells during the refeeding phase, the cells were significantly more likely to cause the formation of precancerous polyps than they were during the fasting phase.

The authors quickly noted that the real-world effects of fasting in humans are much more complex than what we can see in lab mice. So much more research is needed to know if the same changes—good and bad—can be seen in people’s gut stem cells before and after a fast.

“As biological pathways are highly complex and interconnected, the main take home message of our current study is that careful studies should be done to test the effects of any dietary intervention on the human body,” the researchers said.

But the lessons gained here could certainly better inform our understanding of fasting. The researchers found that the fasting mice produced lots of polyamines, organic compounds that play a role in helping cells grow, divide, and turn into other cells, for instance. So they’re now planning to test whether polyamine supplements can be used to easily mimic fasting in future studies. And they hope that these studies will help us make the most of fasting.

“While intermittent fasting is a very popular diet used by millions of humans around the world and has been shown to have immense benefits in multiple diseases, careful dissection of the contribution of each of the fasting phases (fasting vs post-fast refeeding) will give us a greater understanding of how to plan such dietary interventions to maximize regeneration while avoiding increased risk of other diseases such as cancer,” the researchers said.