In recent years, intermittent fasting has emerged as one of the most promising eating patterns. Intermittent fasting is not so much a diet as an eating pattern that cycles between periods of fasting and eating. It’s often used for weight loss, improved metabolism, and potential health benefits like increased longevity and weight loss.

Now, scientists have investigated the pathways through which intermittent fasting promotes cellular regeneration. They also found that too much of this cellular regeneration can be a problem and cause cancerous growth. Although the research was carried out on mice, it could be important for intermittent fasting in humans.

The science of fasting

The study, led by a multidisciplinary team from institutions including MIT and the University of Duisburg-Essen, explored how different dietary conditions affect intestinal stem cells (ISCs) that are crucial for maintaining gut health. They focused on three feeding patterns:

• ad libitum feeding (where food is available at all times);
• fasting;
• refeeding after fasting.

It’s during this “refeeding” period (eating after a period of fasting) that cell regeneration starts to trigger.

“We think that fasting and refeeding represent two distinct states,” Shinya Imada, a postdoctoral researcher at MIT and one of the study’s lead authors, said in a statement.

“In the fasted state, the ability of cells to use lipids and fatty acids as an energy source enables them to survive when nutrients are low. And then it’s the postfast refeeding state that really drives the regeneration. When nutrients become available, these stem cells and progenitor cells activate programmes that enable them to build cellular mass and repopulate the intestinal lining,” he added.

Researchers observed that after the mice underwent refeeding, this triggered a surge in ISC proliferation, boosting their ability to regenerate the intestinal lining. However, this regenerative boost came with a catch.

A potential hazard (with a few caveats)

The study showed that ISCs in the refed state were more likely to give rise to tumors compared to those in the fasted or continuously fed states. This finding suggests that while refeeding is beneficial for tissue repair, it may inadvertently increase cancer risk, particularly in individuals with a predisposition to colorectal cancer.

“Having more stem cell activity is good for regeneration, but too much of a good thing over time can have less favorable consequences,” says Omer Yilmaz, an MIT associate professor of biology, a member of MIT’s Koch Institute for Integrative Cancer Research, and the senior author of the new study.

However, there are a few important caveats. Firstly, as is always the case, studies on mice don’t necessarily mean the same thing in humans. Secondly, intermittent fasting is not a one-size-fits-all practice. In the study, the researchers subjected mice to a 24-hour fasting period, but other regimens exist.

More to learn about intermittent fasting

Future studies will likely explore how different fasting durations, refeeding protocols, and dietary compositions affect ISC behavior and cancer risk. Understanding these nuances could lead to the development of targeted therapies or dietary guidelines that maximize the regenerative benefits of fasting while minimizing the associated risks.

Several previous studies have shown that intermittent fasting can help people lose weight, particularly those suffering from obesity. Research suggests intermittent fasting is also good against Type 2 diabetes and can even help keep you younger genetically.

This new discovery highlights a critical balance between the benefits of tissue regeneration and the potential for increased cancer risk, raising important considerations for the application of fasting and refeeding as a dietary strategy.

“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,” the researchers conclude.

The study was published in the journal Nature.