Intermittent fasting, or intermittent fasting, is hugely popular. It may be very healthy, but the scientific basis for the health claims is weak. New research paints a two-pronged picture. Yes, it extends the lifespan of mice, but no, all that glitters is not gold.

With intermittent fasting, you only eat during a certain period of the day or week. A popular form is not eating for 16 hours a day and eating for 8 hours, but true fanatics, for example, only eat on certain days and not the rest of the week.

Researchers note the period during which people eat. New study The refeeding phase, also called the refeeding phase. Not only in laboratory mice, but also in humans and other organisms, there appears to be an improvement in tissue regeneration during this period after fasting. However, there is a downside to this process: mice also appear to be more susceptible to polyps, the early stage of intestinal tumors, if cancer-causing mutations occur during this regenerative period. The mechanisms that cause this are complex and multifaceted. Researcher Saleh Khawaled from Massachusetts Institute of Technology (MIT) speaks to saintias.nl What fasting does to the body, especially to the cells of the digestive system.

renewal
“Fasting in all its forms has many health benefits,” begins Khawaled. “We distinguish between short-term fasting (sometimes not eating for a day or more), routine periodic fasting (intermittent fasting), and long-term calorie restriction. For example, fasting has been shown to prolong life and promote tissue regeneration. Recent studies also show that fasting also improves the body’s ability to recover from tissue damage – for example, after injuries or infections. This appears to be mainly due to changes in adult stem cells. In addition, fasting diets generally inhibit tumor growth.

Benign tumors
The process by which stem cells are activated occurs during the refeeding phase, when the mice start eating again after a period of fasting. “The main conclusion of our study is that the refeeding phase after fasting is a clearly different phase from fasting itself,” explains Khawald. “When laboratory animals start eating again, the ability of stem cells in the digestive tract to, for example, repair the intestinal wall in case of tissue damage increases. In our research we also discovered that in this refeeding phase, intestinal stem cells become more active. This increases the likelihood of polyps developing if cancer-causing mutations occur in the intestinal cells.”

Greater risk of cancer
The researcher delves deeper into the relationship between polyps and cancer-related mutations during the refeeding phase. “In our research, we discovered that the activity of mTORC1, an important nutrient sensor in our cells, is much greater during the refeeding phase than during the fasting phase. This increased activity leads to increased production and accumulation of polyamines (chemicals that play a critical role in cellular functions such as growth, division, and stress responses) and ultimately to increased protein synthesis in the cells. This creates a much greater amount of these building blocks within the cells, which improves the ability to regenerate. But more importantly, the risk of developing tumors also increases.”

More research is needed.
“It is too simplistic to say that fasting causes cancer in humans,” says Khawald. “We have to be careful with such a statement, as our study was conducted in mice that were fasted in a very specific way, namely 24 hours of fasting followed by 24 hours of refeeding or a three-day refeeding phase. If we want to translate our findings to humans, additional studies in humans are needed. Only then can we say more about the effect of the ratio of fasting to eating, total caloric intake, and meal composition during the refeeding phase in humans.”

However, lead researcher Omer Yilmaz of MIT says, “It leads us to the idea that fasting is very healthy, but if you are unlucky and eat again after fasting and you are exposed to a mutagen, like a charred piece of steak or something like that, you could increase your chances of developing a tumor that could develop into cancer.”

Benefits not burdens
Khawaled did not expect the results. “I was very surprised by the magnitude of the difference between the different fasting phases. Previous studies have mainly focused on the fasting phase, but in our research we refer to the refeeding phase as a special period in which cells develop enhanced regenerative capacity. However, this could also lead to an increased risk of tumor formation if cancer-related mutations occur during the refeeding phase. We are very excited to conduct further research into this.”

“For example, it would also be interesting to study whether repeated cycles of fasting and refeeding, such as so-called ‘asynchronous intermittent fasting regimens’ (e.g. fasting two days a week), could improve stem cell function without leading to more tumors. In other words: no further development of polyps, even though mutations in intestinal cells occur during the refeeding phase.