While previous studies have linked intermittent fasting to benefits such as weight reduction and dementia risk, new research in mice points to a potential downside to periodic food abstinence: an increased risk of cancer.
The discovery follows a previous study that showed that fasting in mice led to an increase in the ability of intestinal stem cells to regenerate, protecting them against damage and inflammation.
Now, an international team of researchers has determined that this increase in stem cell production is accelerated when mice are fed after fasting. Moreover, eating can introduce mutagens – compounds such as heterocyclic amines in burnt meat, which – which increase the risk of cancerous tumors.
“Having more stem cell activity is good for regeneration, but too much of a good thing over time can have less favorable consequences,” says biologist Omer Yilmaz of the Massachusetts Institute of Technology (MIT).
“Fasting is very healthy, but if you’re unlucky and you’re refueling after a fast and you’re exposed to a mutagen, like a charred steak or something, you might actually increase your chances of developing an injury which can give rise to cancer.”
Intestinal stem cells are among the busiest in the body, constantly dividing and growing to renew the gut every 5 to 10 days. This high level of activity also means that cancer-causing aberrations are more likely – and this probability increases even more during the overloaded post-fasting period, he writes.
Intestinal stem cells are among the busiest in the body
The team identified a biological pathway, called mTOR, through which stem cells function. This pathway is involved in cell growth and metabolism, and after fasting increases the production of small molecules called polyamines, which cause cell proliferation.
These molecules are essential in helping the body recover and regenerate after being deprived of the nutrients and energy provided by a regular diet. However, the study shows that the likelihood of tumors also increases, especially in warmer conditions
“We think that fasting and refeeding are two distinct states,” says Shinya Imada, a molecular biologist at MIT. “In the fasting state, the cells’ ability to use lipids and fatty acids as an energy source allows them to survive when nutrients are scarce. Then it’s the recovery state after the fast that really determines the regeneration.”
Two distinct states
Previous studies have suggested that fasting and fasting-mimicking diets could actually be beneficial for, and possibly even enhance, the effectiveness of cancer therapies.
However, studies have largely focused on abstaining from food without considering the potential consequences of breaking the fast.
Further investigation could help identify ways to promote benefits while limiting risks.
As is often the case in such studies, animal models cannot tell us much. The advantages and disadvantages could be completely different in our own species, which requires even more studies to deepen our understanding.
The research was published in
