Intermittent fasting has gained considerable attention for its health benefits, particularly for improving metabolic health. However, a recent study published on December 13 in Cell suggests that this popular dietary practice may come with an unexpected tradeoff: slower hair growth. While this observation was primarily made in mice, a small human study hints at a potential but milder effect in people.
The study, led by stem cell biologist Bing Zhang from Westlake University in Zhejiang, China, highlights a complex relationship between fasting, metabolism, and hair regeneration. Zhang emphasizes that the findings should not deter people from intermittent fasting, which offers significant health benefits, but rather raise awareness of its possible unintended effects.
Previous research has already established that fasting can bolster the stress resistance of various stem cells, such as those associated with blood, intestines, and muscles. However, little was known about its impact on peripheral tissues like skin and hair. Zhang’s team hypothesized that fasting might enhance skin tissue regeneration, given its beneficial effects in other tissues. The results, however, revealed a surprising downside for hair follicle stem cells (HFSCs), which are critical for hair regrowth.
The researchers conducted their experiments on mice, dividing them into groups with different fasting regimens. One group followed a time-restricted feeding (TRF) schedule, where they ate for 8 hours and fasted for 16 hours daily. Another group was subjected to alternate-day feeding (ADF), where they ate one day and fasted the next. A control group had continuous access to food. To measure hair regrowth, the researchers shaved the mice and observed their hair regeneration over time.
The results showed a stark difference in hair growth between the groups. Control mice, which ate freely, regrew most of their hair within 30 days. In contrast, mice on intermittent fasting regimens displayed only partial hair regrowth even after 96 days. This suggested a significant delay in the hair regeneration process due to fasting.
To understand the cause, the researchers turned their attention to HFSCs, which are responsible for cycling between periods of dormancy and activity to enable hair growth. These stem cells were unable to handle the oxidative stress associated with the metabolic switch from glucose to fat during fasting. This metabolic shift led to a build-up of harmful reactive oxygen species (ROS), causing the HFSCs to undergo apoptosis, or programmed cell death. By comparison, HFSCs in the control mice became active around day 20 post-shaving and remained so until hair regrowth was complete.
The researchers identified the culprit behind the fasting-induced damage: free fatty acids. During fasting, adipose tissue releases these fatty acids, which accumulate near the hair follicles. When absorbed by HFSCs, the fatty acids overwhelmed the cells, triggering oxidative damage. Zhang explained that HFSCs lack the necessary mechanisms to efficiently utilize these fatty acids, making them vulnerable to damage during extended fasting periods.
Interestingly, the effects of fasting were specific to HFSCs. Epidermal stem cells, which are responsible for maintaining the skin barrier, remained unaffected. The team attributed this difference to the higher antioxidant capacity of epidermal stem cells, which helps them neutralize oxidative stress more effectively. To explore potential solutions, the researchers tested whether antioxidants could protect HFSCs during fasting. Both the topical application of vitamin E and genetic enhancements to increase antioxidant capacity significantly improved HFSC survival and hair regrowth.
To investigate whether similar effects occur in humans, Zhang’s team conducted a small clinical trial involving 49 healthy young adults. Participants followed an 18-hour fasting regimen each day for 10 days. The study found that hair growth speed decreased by 18% in the fasting group compared to controls. However, the researchers cautioned that the human effects were much milder than those observed in mice, likely due to differences in metabolic rates and hair growth patterns between the two species. Humans have slower metabolic rates, which means the metabolic switching induced by fasting is less extreme. Additionally, while some human HFSCs underwent apoptosis, many survived, enabling continued—albeit slower—hair regrowth.
Given the small sample size and short duration of the clinical trial, Zhang emphasized the need for larger, more diverse studies to confirm these findings. He noted that individual differences in metabolism, genetics, and lifestyle could influence the extent of fasting’s effects on hair growth in humans.
The study raises intriguing questions about how fasting might impact other types of stem cells and tissue regeneration processes. Zhang and his team plan to collaborate with hospitals to explore these broader implications. They aim to investigate how fasting affects skin wound healing and the regeneration of other tissues, as well as identify metabolites that could enhance HFSC survival and promote hair growth during fasting.
While intermittent fasting remains a valuable tool for improving overall health, this research highlights the importance of understanding its broader physiological effects. For those concerned about hair health, incorporating antioxidant-rich foods or topical treatments may help mitigate potential downsides. Zhang’s work underscores the complex interplay between diet, metabolism, and tissue regeneration, paving the way for a more nuanced approach to fasting and its long-term effects on the body.
Source: Cell Press