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Previous research has tied intermittent fasting to benefits like weight loss and a lower risk of dementia. But a new study led by researchers at the Massachusetts Institute of Technology (MIT) finds this kind of fasting may also raise the risk of cancer.
This builds on the team’s earlier work, which showed that fasting in mice boosted the regenerative abilities of intestinal stem cells and protected against injury and inflammation. Now the researchers have reached a more alarming conclusion.
What Did the Scientists Discover?
The team found that stem-cell production in mice accelerates when the rodents start eating normally again after intermittent fasting. At that time, food can introduce mutagens into the body—compounds such as heterocyclic amines found in charred meat—that can cause genetic mutations and increase the risk of tumor formation.
“High stem cell activity is beneficial for regeneration, but an excess of this beneficial factor over time may have less favorable consequences,” said Omer Yilmaz, a biologist at MIT and the lead author of the study.
Yilmaz said, “Fasting is very beneficial, but if you’re recovering from it and then exposed to a mutagen, like a charred steak, there’s a chance of developing cancer.”
Intestinal stem cells are among the body’s most active cells. They divide constantly to rebuild the intestine roughly every 5 to 10 days. That high turnover makes cancer-causing errors more likely, and Science Alert reports the risk climbs even higher during the post-fasting surge in stem-cell activity.
The team pinpointed the mTOR pathway as central to stem-cell behavior. mTOR controls cell growth and metabolism, and after fasting it boosts production of polyamines—small molecules that stimulate cell proliferation.
Polyamines help the body recover and regenerate after nutrient deprivation during fasting. But the study also found that higher polyamine-driven proliferation raises the chance of tumor development.
What Are the Conclusions?
Previous studies have suggested that fasting and certain diets can lower cancer risk and even make cancer therapies more effective. But those studies mostly focused on the fasting itself and didn’t examine potential downstream consequences.
The team is planning further research to find ways to keep the benefits of intermittent fasting while reducing the risks.
As with many studies, results from animal models are limited. The researchers plan to follow up with human studies.
The study appears in the journal Nature.
