This popular diet may increase cancer risk
Key Takeaways
Intermittent fasting is a popular weight loss strategy with many known health benefits.
Research on mice demonstrated how intestinal cells proliferate more rapidly during the post-fast refeeding window.
Although rapid cellular regeneration is generally considered beneficial, there’s potential for harm when genetic conditions are favorable for cancer growth.
Most people take one of two approaches to weight loss: They restrict calories by monitoring what they eat, or they use intermittent fasting (IF) to limit how much time they spend eating and digesting food.
IF has gained popularity as a health trend, and proponents say its positive effects extend beyond weight loss. However, a recent study from MIT in mice calls the assumed longevity and anti-cancer benefits of IF into question.[]
IF and intestinal mutations
Past research indicates that fasting enhances the regenerative power of stem cells in the intestines, promoting healing and reducing inflammation.[] This effect is usually considered beneficial.
However, the new findings from MIT suggest that rapid regeneration may promote cancer if refeeding happens when genes known to cause cancer are turned on. As intestinal cells are one of the most frequently dividing types of cells in the body, they may be especially vulnerable to cancerous mutations during this post-fast refeeding state.[]
The 2024 study by the MIT researchers, published in Nature, examined mice after short-term fasting.[] Researchers studied three groups of mice. One had unrestricted food access, another fasted for 24 hours, and a third fasted for 24 hours, followed by an unrestricted refeeding period. Intestinal stem cell activity was assessed over multiple time points.
Cell proliferation was the greatest during the refeeding phase after the 24-hour fast, suggesting that post-fast refeeding leads to an exceptional surge in cellular regeneration.[]
The authors wrote, “Given our findings, fast-refeeding cycles must be carefully considered and tested when planning diet-based strategies for regeneration without increasing cancer risk, as post-fast refeeding leads to a burst in stem-cell-driven regeneration and tumorigenicity.”
They identified the post-fast refeeding period as a distinct state with greater potential for tumor proliferation compared to the fasted or continuously fed state.[]
Potential implications for humans
It’s important to note that the MIT study was done on mice, not humans. Humans are more complex creatures, and the real-world application of tightly controlled lab conditions can be difficult to bridge. Nonetheless, these findings suggest that special care should be taken in the refeeding process after fast. Avoiding carcinogens during this vulnerable time may make the difference between healthy cell regeneration and the proliferation of cancer.[]
Findings that suggest IF promotes cancer are contradictory to a large body of research supporting the benefits of fasting. A 2022 review by international researchers found IF to be a successful method for reversing diabetes, hypertension, hyperlipidemia, and thyroid dysfunction.[] They also cited research supporting the therapeutic potential of IF for preventing and treating neurodegenerative diseases and cancer.
Specifically, fasting has also been shown to reduce cancer in multiple ways. It reduces obesity, lowers insulin and blood sugar levels, induces autophagy, and promotes anticancer immune responses.[] It may also support the effectiveness of cancer treatment, especially chemotherapy, and healing after radiation treatment.
However, there’s an unexplored possibility that any anticancer effects of IF are associated with the fasted state itself, not the refeeding period that so quickly follows popular shorter-term IF regimens.
The recent study on mice certainly raises important questions about the best conditions for fasting and refeeding. Parsing out the specific cellular chain of events that follow an intermittent fast could help shed more light on any relationship between fasting and cancer.
What this means for you
A 2024 MIT study describing fasting’s effects on cellular regeneration in mice yielded some startling findings, but at the same time left unanswered questions about the ideal fasting protocol for humans, given diverse genetic backgrounds and lifestyles. Although fasting has many established health benefits, there may be certain circumstances where it brings unintended consequences. The refeeding state is a particular area of interest that warrants more investigation.