Intermittent fasting, a popular eating pattern praised for its potential benefits to metabolic health, may have an unexpected downside: it could suppress hair growth. A recent study on mice and a small human clinical trial reveals that while the effect on people is less pronounced, intermittent fasting may still lead to reduced hair growth. This finding suggests that individuals experiencing hair loss should exercise caution before committing to intermittent fasting.
A research team led by Professor Bing Zhang from Zhejiang University in China published its findings in the prestigious journal Cell. The study revealed that while mice on an intermittent fasting regimen improved their metabolic health compared to those with continuous access to food, their hair growth was noticeably slower. Researchers believe this is due to the buildup of reactive oxygen species (ROS) during fasting, which can cause apoptosis (cell death) of hair follicle stem cells (HFSCs).
In a small clinical trial with humans, a similar effect was observed. However, because of humans’ slower metabolism and different hair growth patterns, hair growth suppression was less severe than in mice.
Zhang and his team explained, “Previous studies have shown that fasting can enhance the stress resistance of stem cells in the blood, gut, and muscle tissues, alongside its metabolic benefits. However, the impact of fasting on peripheral tissues like the skin and hair has remained largely unexplored until now.”
The research team divided shaved mice into three groups to explore this further. One group (TRF) followed a daily intermittent fasting regimen, eating within an 8-hour window and fasting for 16 hours. Another group (ADF) practiced alternate-day fasting, while the third group (AL) had unrestricted access to food 24/7.
The results were striking. While the control group of mice, which had continuous access to food, saw most of their fur regrow after just 30 days, the fasting groups—both the intermittent fasting group (8–16 hours) and the alternate-day fasting group (ADF)—showed partial fur regrowth only after 96 days.
The research team also focused on the impact of intermittent fasting on hair follicle stem cells (HFSCs). In the control group, which had 24/7 access to food, HFSCs activated by day 20 after shaving and remained active. However, HFSCs experienced cell death during fasting periods in both the intermittent and alternate-day fasting groups.
The researchers explained that this cell death occurred due to increased free fatty acids released from adipose (fat) tissue during fasting. These fatty acids lead to the accumulation of harmful reactive oxygen species in the hair follicles. The researchers found that free fatty acids had a similar cell-killing effect on human HFSCs in laboratory tests.
The research team also conducted a 10-day clinical trial involving 49 healthy young adults to study the effects of an 18-hour intermittent fasting regimen on hair growth. The results were consistent with the findings in mice, showing that the hair growth rate in the intermittent fasting group was 18% slower compared to the control group.
Zhang pointed out the differences between humans and mice: “Humans have significantly slower metabolic rates and distinct hair growth patterns compared to mice, so the effects of intermittent fasting could vary significantly between species.” He added, “While intermittent fasting has many beneficial effects, I don’t want to discourage people from trying it. However, it’s important to be aware of potential unintended consequences, especially for those concerned about hair loss.”