Intermittent fasting may be stopping your hair from growing – here’s why
Intermittent fasting – including popular diets such as the 5:2 diet and the fast 800, where you eat during a set time window each day – has been credited by both celebrities and dieticians, as the secret to staying slim.
But, according to researchers at Westlake University in China, fasting has a potential drawback: it could slow hair growth.
The research
Led by Dr Bing Zhang, senior author and stem cell biologist of Westlake University in Zhejiang, the study, published in the journal Cell, aimed to explore how fasting influences tissue regeneration, particularly in hair follicles.
The method
The researchers began with experiments on mice. Groups of mice were either placed on fasting schedules, eating only during a restricted window (where eating was limited to an 8-hour window each day, followed by 16 hours of fasting), or every other day (where mice alternated between 24 hours of fasting and 24 hours of unrestricted eating), or allowed to eat freely. The mice were shaved, and their hair regrowth was tracked for 96 days.
The team also conducted a small-scale study on 49 young adult humans to see if similar effects could be observed in people. The researchers shaved 1sq cm of their scalps and then measured the length of the hair three days later.
The scientists examined how fasting influences hormones and cellular metabolism – looking specifically at how fasting might affect the energy supply to hair follicle stem cells, which are crucial for hair regeneration.
The results
The results in mice showed that intermittent fasting had a significant effect on hair regrowth. Mice with unrestricted diets regrew their shaved hair within 30 days. While those on fasting diets had large bald patches even after 100 days.
In the human study, the effects weren’t as dramatic, but still notable.
Participants following the 18:6 fasting diet had an 18% slower hair regrowth rate than those who ate normally. And while hair density did not show significant differences, regrown hairs in fasting participants were both thinner and shorter.
‘The human population is very heterogeneous, so the effects might be different for different people,’ said Dr Zhang.
‘Mice also have a very high metabolic rate compared with humans, so fasting and metabolic switching have a more severe effect on mouse hair follicle stem cells (HFSCs). We see a milder effect in humans; there are still apoptotic stem cells, but many HFSCs survive. So, there is still hair regrowth; it's just a little bit slower than usual.’
What does this mean for us?
While there are lots of health benefits associated with intermittent fasting, this study shows that fasting could impair hair growth. Although the effects were more pronounced in mice than in humans, the findings suggest that fasting may trigger ancient. biological mechanisms
‘During evolution, both wild animals and our human ancestors faced environments with fluctuating food availability, making fasting a regular occurrence,’ write Dr Zhang and his co-authors in their study.
‘Our identified mechanism may enable them to halt peripheral tissue regeneration to conserve resources for more critical organs like the brain, thereby promoting adaptation and survival.’
Adding that, ‘Intermittent fasting may inadvertently activate this ancient mechanism, resulting in unintended effects on hair follicle regeneration and hair growth.’
The bottom line
Given the study's small sample size, larger studies would be needed to verify this effect of fasting.
But, for those practising intermittent fasting, these findings act as a reminder that not every diet is suitable for everyone (and there can be potential downsides).
‘We don't want to scare people away from practicing intermittent fasting because it is associated with a lot of beneficial effects; it's just important to be aware that it might have some unintended effects,’ said Dr Zhang.
So, if you’re currently on a hair growth mission, it’s perhaps best to opt for a balanced, nutritious diet, with consistent eating patterns. And, if you want to fast, remember to always chat to your doctor or nutritionist first.
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