While intermittent fasting is undoubtedly a huge boon for those looking to lose weight, build muscle, and even keep heart disease at bay, a new study has revealed that it may have a potentially lethal health implication that might make you reconsider before diving into this dieting trend headfirst. Here, we take a well-rounded look at the study’s findings — including what it suggests are still very legitimate advantages of the time-based approach to dieting — but also its deadly downside…

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The Downside Of Fasting

Researchers at MIT, led by Associate Professor Omer Yilmaz, have uncovered a fascinating but undeniably alarming link between intermittent fasting and increased cancer risk in mice. Their study, published in Nature and on ScienceDaily, suggests that while fasting promotes the regeneration of intestinal stem cells — which is unequivocally a good thing — it may also create a fertile ground for cancerous growths when followed by a so-called “refeeding” period. Yilmaz explained:

“Having more stem cell activity is good for regeneration, but too much of a good thing over time can have less favourable consequences.”

The study suggests that during the refeeding phase, after a period of fasting, intestinal stem cells became highly proliferative. This surge in cellular activity, while beneficial for healing, also increased the likelihood of developing early-stage intestinal tumours if and when cancerous mutations occurred.

mTOR Pathways

The study focused closely on the cellular mechanisms behind this phenomenon, specifically the mTOR signalling pathway. During fasting, stem cells in the intestine switch to using lipids as an energy source. However, once refeeding begins, the mTOR pathway is activated, leading to a rapid increase in protein synthesis and cell proliferation… sounds complicated, and it is, but MIT postdoc Shinya Imada, another lead author of the study, clarifies:

“Fasting and refeeding represent two distinct states… In the postfast refeeding state, stem cells and progenitor cells activate programs that enable them to build cellular mass and repopulate the intestinal lining.”

However, this intense regeneration can also lead to the production of polyamines — small molecules that drive cell growth. While this is crucial for repair, it also creates conditions where cancerous cells can thrive. Mice exposed to cancer-causing mutations during the refeeding phase were significantly more likely to develop precancerous polyps than those exposed during fasting or — potentially crucially for human lifestyles — without fasting altogether.

Implications For Human Health

While these findings are based on mouse models — which provides an obvious limit to how urgent their findings should be considered — the implications for human health are nevertheless concerning. Yilmaz cautioned that further research is needed to understand how intermittent fasting and refeeding might affect cancer risk in humans.

“In humans, it’s going to be a much more complex state,” he noted before adding that the study underscores the need for caution when combining fasting with certain dietary habits, particularly those involving mutagenic foods like charred meats. Yilma rounds out his commentary with a stark warning:

“Fasting is very healthy, but it can come with a hidden cost that we are only beginning to understand.”