Many benefits are known for intermittent fasting, as it can help lose weight while improving metabolic health by using the body’s fat for energy. However, not all organs or cells respond to fasting similarly. A recent report in the Cell has shown that intermittent fasting can reduce hair growth in humans and mice. This is mainly due to the death of hair follicle stem cells (HFSCs), not allowing their growth and differentiation to new hair follicles.
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Human study
49 healthy young adults including both males and females were enrolled in the study in China (clinical trial – NCT05800730). They were randomized into three groups: (a) 18/6 time-restricted diet – 18h of fasting with 6 h of feeding, (b) energy-restricted diet – 1200-1500 kcal/day, and (c) control group with normal diet. Hair growth was measured by shaving a 1 cm2 region on the scalp and observing new hair after 3 days. They found that both time-restricted and energy-restricted diets reduced hair growth by 18% compared to the control group. The new regrown hair were shorter and thinner in diameter.
Mice study
Similar to humans, mice on intermittent fasting also had reduced hair growth after shaving. This was due to apoptosis of the hair follicle stem cells (HFSCs). Interestingly, they found that HFSCs get activated after shaving but when encountered fasting undergo apoptosis to save nutrients for essential body functions. Repetitive activation and apoptosis of HFSCs ultimately led to reduced hair growth.
Figure: Summary of the study. Made in bioRender
Mechanistically, they ruled out the involvement of circadian rhythm or mTORC1-mediated nutrient sensing mechanism in hair loss. They found that lipid oxidation caused the HFSCs apoptosis. As inhibiting lipolysis reduced their apoptosis, and hair growth became normal during fasting. Lipolysis produced reactive oxygen species that caused apoptosis of HFSCs. Finally, to connect the dots they found that intermittent fasting-induced stress hormones – cortisol and epinephrine – led to lipolysis in HFSCs. Strikingly, mice without adrenal glands were resistant to intermittent fasting-induced hair loss. Encouragingly, hair loss was prevented by applying antioxidant vitamin E cream to the skin, indicating that it can be treated when fasting.
Caveats of the study
- The study did not examine similarities or differences between age- and fasting-induced apoptosis of HFSCs. It would be interesting to determine the mechanistic insights.
- The authors did not test the lipolysis in human hair follicles due to technical challenges.
- The effect of intermittent fasting-induced hair loss was not studied in obese or metabolically unhealthy individuals.
- Long-term effects of intermittent fasting on hair growth and hair shaft density were not evaluated.
