Intermittent fasting can lengthen your lifespan and aid weight loss – but can you have too much of a good thing? Well, yes – according to a new MIT study, which has found that there could be a dark side to the regenerative powers of fasting.
The researchers behind the study, published in journal Nature, identified the pathway in the intestines of mice activated by fasting. This pathway is crucial for boosting regeneration in stem cells – an important process for healing injuries.
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They discovered that the pathway was activated when the mice began to eat again after fasting. But there was also a downside: cancerous mutations caused by regeneration were more likely to develop into early-stage tumours.
“Having more stem cell activity is good for regeneration, but too much of a good thing over time can have less favourable consequences,” said Prof Omer Yilmaz, senior author of the study.
Stem cells divide frequently, helping the lining of the intestine completely renew every 5-10 days – but this makes them the a common source of pre-cancerous cells.
To find out the effect of fasting on stem cells, Yilmaz and his team split the mice into three groups: one that fasted for 24 hours, one that fasted for 24 hours and then ate whatever they wanted for 24 hours (known as the ‘refeeding’ period), and a control group that did not fast and ate as they wanted for the entire time.
They found that stem cells proliferated the most at the end of the refeeding period – much more than the stem cells in the mice that had not fasted at all. This intense regeneration is caused by nutrients becoming available again, which causes the stem cells to activate a cellular pathway known as mTOR. mTOR triggers other cells to produce more protein, which the stem cells need to divide and proliferate –going on to build more specialised cells.
But in this highly regenerative state, they’re more prone to becoming cancerous. When the researchers turned on a cancer-causing gene in the mice DNA, during both the fasting stage and in the refeeding stage, they found that cancerous polyps were much more likely to develop during refeeding.
“I want to emphasise that this was all done in mice, using very well-defined cancer mutations. In humans it's going to be a much more complex state,” Yilmaz said.
“But it does lead us to the following notion: Fasting is very healthy, but if you're unlucky and you're refeeding after a fasting, and you get exposed to a mutagen, like a charred steak or something, you might actually be increasing your chances of developing a lesion that can go on to give rise to cancer.”
The researchers emphasise that human trials are needed to confirm the results in people. Next, they plan to investigate whether polyamine supplements, which are said to boost cell growth, could stimulate regeneration without needing to fast.
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