Gaby
Researchers at Westlake University in Zhejiang, China have found an unexpected side effect of the increasingly popular practice of intermittent fasting: it can slow hair regeneration. While intermittent fasting has known health benefits and is safe for most people, the team says hair regrowth appears to be one cost of the metabolic switch that fasting causes.
The researchers reached this conclusion after running noninvasive experiments on mice and a small clinical study in humans.
The study’s senior author, Bin Zhang, a stem cell biologist, said the finding shouldn’t overshadow the potential advantages of intermittent fasting, but it does serve as a reminder that health interventions can have trade-offs.
Previous work suggested that intermittent fasting boosts stress resistance in certain stem cells, especially those in blood, intestines, and muscle. But how fasting affects peripheral tissues such as skin and hair was not well understood.
How Was the Study Conducted?
The university team divided shaved mice into three groups: two intermittent-fasting groups and one control group with unrestricted access to food. The scientists then closely monitored hair regrowth in each group.
The first fasting group had access to food for 8 hours each day and fasted for 16 hours. The second group alternated between 24 hours eating and 24 hours fasting. It soon became clear that the fasted mice experienced slower hair regrowth.
In both intermittent-fasting groups, hair regrowth was only partial after 96 days. By contrast, control mice had regrown their hair within 30 days, according to ScienceAlert.
Why Does This Happen?
Diving deeper, the researchers found that hair follicle stem cells (HFSCs) struggle to cope with the imbalance of free radicals and antioxidants that comes with switching the body’s fuel source from glucose to fat.
HFSCs naturally cycle between an active phase and a resting phase. New hair can only grow if those stem cells transition back to an active state.
In the control mice, HFSCs returned to activity about 20 days after shaving and stayed active until hair regrew. In the fasting rodents, many of those stem cells underwent apoptosis, or programmed cell death, during prolonged periods without food.
The team linked this to a sharp increase in free fatty acids around the hair follicles, which led to a buildup of reactive oxygen species inside the stem cells.
“During fasting, adipose tissue releases free fatty acids that enter recently activated hair follicle stem cells, but these stem cells lack the necessary mechanisms to use that fuel,” Dr. Zhang explained.
By contrast, the outer layer of skin cells appeared unaffected by fasting, likely because those cells have higher antioxidant capacity. The researchers also found HFSCs were less vulnerable to fasting-induced apoptosis when they increased the stem cells’ antioxidant capacity by applying vitamin E topically.
What About Humans?
In a small clinical study, the scientists enrolled 49 healthy young adults to see if the mouse findings matched human biology.
The volunteers fasted for 18 hours each day and ate during a 6-hour window. Their hair regrew more slowly than the control group, who had unrestricted access to food. The team says longer studies with larger sample sizes are needed to fully understand the connection.
The researchers also plan to investigate how other tissues respond to fasting and what mechanisms are involved across the body.
The results were published in the journal Cell.
