Many Americans try intermittent fasting, hoping to get healthier and lose weight.
According to Johns Hopkins Medicine, intermittent fasting has been shown to boost thinking and memory, improve heart health and physical performance, aid in the curtailing of type 2 diabetes, and improve tissue health.
With all the potential benefits, new research suggests a possible unwelcomed side effect: intermittent fasting might also slow hair growth.
In a study published online in Cell on December 13, 2024, scientists found that when they shaved mice and put them on intermittent fasting diets—either eating for 8 hours and then fasting for 16 hours or fasting every other day—the mice didn’t grow back their hair as quickly as those who could eat anytime.
Additionally, the mice that ate regularly had most of their hair back after 30 days, while the fasting mice only had some hair regrowth after 90 days.
Research shows that common intermittent fasting methods can hinder hair follicle regeneration by causing programmed cell death, or apoptosis, in activated hair follicle stem cells.
To better understand how intermittent fasting affects hair growth, researchers tried two popular fasting schedules: 16/8 time-restricted feeding (TRF) and alternate-day fasting (ADF).
In the TRF method, food intake is limited to 8 hours each day, followed by a 16-hour fasting period, while ADF involves 24 hours of fasting followed by 24 hours of unrestricted eating.
Researchers conducted the experiment on adult mice starting from a specific age when their hair follicles were in a resting phase.
Over 96 days, scientists observed that mice with regular access to food began regrowing hair, while those on TRF and ADF diets showed much slower regrowth.
Microscopic examination of the hair follicles revealed they remained in a prolonged resting stage and failed to produce new hair. These effects were consistent across all tested mice, regardless of gender or age when the fasting began.
Although intermittent fasting improved metabolic health in mice, it significantly hindered hair follicle regeneration.
Researchers think this might happen because the special cells needed for hair growth can become stressed when the body switches how it gets energy, switching from using sugar to fat during fasting.
Similar results were seen in a small study with 49 healthy young adults. Those who practiced intermittent fasting for 18 hours each day grew their hair about 18% slower than those who followed a regular eating schedule, per a peer-reviewed Cell press release.
“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 Bing Zang, PhD, senior author of the study, per the Cell press release.