A team of researchers from Westlake University in Zhejiang, China, has uncovered an unexpected effect of the increasingly popular practice of intermittent fasting. While scientists have long recognized its health benefits and safety for most practitioners, it turns out that one consequence of intermittent fasting is a slowdown in hair regeneration.
The researchers reached this conclusion after conducting non-invasive experiments on mice, as well as a small clinical study involving humans.
This news shouldn’t overshadow the potential advantages of intermittent fasting, noted the study’s senior author, Bin Zhang, a stem cell biologist. However, he believes it serves as a reminder that any health benefits may come with unexpected side effects.
Previous studies suggested that intermittent fasting enhances the stress resistance of certain stem cells, particularly those related to blood, the intestines, and muscle tissue. However, it was unclear how it affected peripheral tissues, such as skin or hair.
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.
It’s important to clarify that the rodents in the first group had access to food for 8 hours and fasted for 16 hours. Participants in the second group alternated between 24 hours of eating and 24 hours of fasting. It soon became evident that the mice undergoing fasting experienced slower hair regeneration.
In both groups of mice subjected to intermittent fasting, hair regrowth was only partial after 96 days of the study. Meanwhile, the control group mice had already regrown their hair within 30 days, according to Science Alert.
Why Does This Happen?
Diving deeper, the researchers discovered that hair follicle stem cells (HFSC) struggle to cope with the imbalance of free radicals and antioxidants caused by the switch between glucose and fat.
HFSC naturally alternate between an active phase and a resting phase. New hair can only grow if the stem cells transition back to an active state.
The study showed that in the control group of mice, HFSC returned to activity just 20 days after shaving and remained active until the hair regrew. However, in the fasting rodents, these cells underwent apoptosis (programmed cell death) during prolonged periods without food.
The researchers linked this to a sharp increase in free fatty acid levels around the hair follicles, which led to the accumulation of reactive oxygen species in the stem cells.
“During fasting, adipose tissue begins to release free fatty acids, which enter the recently activated visceral stem cells, but these stem cells lack the necessary mechanisms to utilize them,” explained Dr. Zhang.
On the other hand, the outer layer of skin cells appeared unaffected by fasting. This may be due to their higher antioxidant capacity. HFSC also proved less vulnerable to fasting-induced apoptosis when researchers genetically enhanced their antioxidant ability by applying the antioxidant vitamin E topically.
What About Humans?
In a small clinical study, the scientists involved 49 healthy young individuals. The goal was the same: to understand how intermittent fasting affects hair growth.
The volunteers fasted for 18 hours a day and had a 6-hour eating window. It turned out that their hair regrew more slowly than that of participants in the control group, who had unrestricted access to food. According to the researchers, longer studies with larger sample sizes are needed for a more comprehensive understanding of this connection.
The researchers also plan to investigate how other tissues respond to fasting and what mechanisms are involved in the body during this process.
The results of the study were published in the journal Cell.