Intermittent fasting has been linked to benefits such as weight loss and reduced dementia risk. However, new research in mice suggests that this practice might have a downside: an increased risk of cancer.
An international team of researchers discovered that while fasting in mice boosts the regenerative abilities of their intestinal stem cells, this benefit may come at a cost. When the mice refeed after fasting, the increased stem cell activity can introduce mutagens compounds like those found in burned meats that raise the risk of developing cancerous tumors.
“Having more stem cell activity is good for regeneration, but too much of a good thing can have negative consequences,” says biologist Omer Yilmaz from the Massachusetts Institute of Technology (MIT). He explains that while fasting is generally healthy, the refeeding phase might increase the chances of cancer, especially if mutagens are introduced during this period.
Intestinal stem cells, which constantly renew the intestine every 5 to 10 days, are highly active and therefore more prone to cancer-causing mutations. The study showed that this risk increases during the post-fasting period when cell activity is at its peak.
The researchers identified a biological pathway called mTOR, which is involved in cell growth and metabolism. After fasting, this pathway increases the production of molecules called polyamines, which drive cell proliferation. While these molecules help the body recover after fasting, they also raise the risk of tumor formation in conditions favorable to cancer growth.
“We think fasting and refeeding represent two distinct states,” says MIT molecular biologist Shinya Imada. During fasting, cells use lipids and fatty acids for energy. But after fasting, when the body refuels, it triggers rapid regeneration.
Previous studies have suggested that fasting might reduce cancer risk and even enhance the effectiveness of anti-cancer therapies. However, these studies have focused on fasting itself, without considering the potential risks of refeeding.
More research is needed to find ways to maximize the benefits of fasting while minimizing the risks. It’s important to note that this study was conducted in mice, and the results may not directly apply to humans, where the situation is likely to be more complex.
“I want to emphasize that this was all done in mice, using very well-defined cancer mutations,” says Yilmaz. “In humans, it’s going to be a much more complex state.” The research has been published in Nature.
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