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Here’s some hair-raising news for dieters.
A buzzy eating plan praised for helping with weight loss, blood sugar and inflammation could have a majorly unpleasant side effect — your luscious locks may lose their volume.
A new study found that mice subjected to intermittent fasting — which involves limiting eating to a certain daily window — had better metabolic health but slower hair growth than mice with round-the-clock access to food.
And when they studied the same thing in humans, they found similar results.
“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 senior study author and stem cell biologist Bing Zhang of Westlake University in China.
How fasting can affect hair
Research indicates that intermittent fasting can improve the function of stem cells in blood, intestinal and muscle tissue — and their ability to regenerate. Zhang’s team wanted to see the effect of fasting on skin and hair cells.
The researchers had shaved mice follow a daily meal schedule that allowed only eight hours of food access, with 16 hours of fasting, or an alternate-day feeding plan.
Mice on both intermittent fasting programs had only partial hair regrowth after 96 days, while mice with unlimited access to food had regrown most of their hair after 30 days — a finding that surprised the researchers.
The team determined that fasting selectively eliminates activated hair follicle stem cells (HFSCs). Hair regrowth depends on these cells being active.
The science behind intermittent fasting
Intermittent fasting forces the body to use stored fat as its primary energy source instead of readily available sugar from food.
The body fat releases free fatty acids that enter recently activated HFSCs, causing damage and even cell death.
Applying vitamin E, an antioxidant found in hair growth products, twice a day to the back skin of mice helped HFSCs survive fasting.
Skin stem cells were unaffected by intermittent fasting, with the researchers crediting their ability to neutralize harmful free radicals.
The researchers tried to confirm their findings with a small clinical trial that included 49 healthy young adults — they noticed fasting had a milder effect on hair regrowth in humans.
Those who fasted 18 hours a day for 10 days — an extreme version of the diet — had an average hair regrowth speed that was 18% slower compared to those who didn’t fast. Larger and longer studies would be needed to verify this outcome.
“The human population is very heterogeneous, so the effects might be different for different people,” Zhang said. “Mice also have a very high metabolic rate compared with humans, so fasting and metabolic switching have a more severe effect on mouse HFSCs.”
What’s next
The results were published Friday in the Cell Press journal Cell.
The researchers plan to collaborate with local hospitals to explore how fasting affects wound healing and the regeneration of other cells while identifying substances that could help promote hair growth during fasting.
Long before this research, medical experts warned that intermittent fasting is not for everyone. A major study from this year found that those who restricted eating to less than eight hours a day are more likely to die from cardiovascular disease than people who eat in a 12- to 16-hour window.
