Intermittent fasting (IF), a popular dietary trend embraced by over 10% of U.S. adults in 2023, has been celebrated for its potential metabolic benefits, including fat loss and improved cardiovascular health. However, emerging research highlights a previously unrecognized drawback: its impact on hair growth. This article explores the science behind IF’s metabolic switch, its documented health advantages, and new findings from both animal and human studies indicating that IF may suppress hair follicle regeneration. By examining the mechanisms linking fasting to oxidative stress and hair follicle stem cell apoptosis, this piece aims to provide a balanced view of IF’s benefits and risks, empowering readers to make informed decisions about adopting such diets.
Intermittent fasting operates on the principle of metabolic switching. Normally, the body relies on glucose and liver glycogen for energy. When food intake is restricted—whether through daily fasting windows (e.g., 16:8 method) or alternate-day fasting—the body depletes glycogen stores and shifts to ketone metabolism, utilizing fatty acids for energy. This transition, studied extensively in rodents and humans, is associated with:
- Fat mobilization: Enhanced breakdown of adipose tissue into free fatty acids (FFAs) and ketones like β-hydroxybutyrate.
- Muscle preservation: Ketones help maintain muscle mass by sparing amino acids, a key advantage over continuous caloric restriction .
- Cellular adaptation: Activation of signaling pathways like AMPK and SIRT1, promoting mitochondrial health, autophagy, and stress resistance .
Proponents of IF highlight its potential to improve body composition, reduce insulin resistance, and lower risks of metabolic diseases . For instance, human trials show IF can decrease visceral fat, fasting glucose, and LDL cholesterol while preserving lean mass in overweight individuals .
While IF’s metabolic benefits are well-documented, a recent study by Prof. Bing Zhang’s team at Westlake University reveals a surprising downside: inhibited hair regrowth. Using mouse models, researchers compared two IF protocols—16:8 fasting and alternate-day fasting—against ad libitum feeding. Key findings included:
- Delayed hair regeneration: Normal mice regrew hair within 30 days post-shaving, while IF-fed mice showed incomplete regrowth even after 90 days .
- Stem cell apoptosis: IF triggered oxidative stress in hair follicle stem cells (HFSCs), leading to their death. The metabolic shift to ketone production increased FFAs around hair follicles, which HFSCs cannot metabolize efficiently. This imbalance generated reactive oxygen species (ROS), causing DNA damage and apoptosis .
Intermittent fasting may inhibit hair follicle regrowth
In a small human clinical trial involving 49 healthy volunteers, 18-hour daily fasting induced mild HFSC apoptosis. While human hair regrowth was not completely halted, it slowed by ~18% compared to non-fasting controls . Notably, the effect was less severe in humans due to slower metabolism and longer hair growth cycles, but the mechanism mirrored findings in mice.
The interplay between IF and hair health revolves around organ communication and metabolic stress:
-
Free Fatty Acids (FFAs) and Oxidative Stress:
During ketone metabolism, FFAs accumulate in tissues, including the skin. HFSCs lack the enzymes to process excess FFAs, leading to ROS buildup and mitochondrial dysfunction .
-
Stem Cell Dormancy vs. Death:
Normally, HFSCs cycle between quiescence and activation. IF disrupts this rhythm, pushing cells toward apoptosis instead of reactivation, as observed in shaved mice where HFSCs failed to exit dormancy .
-
Potential Mitigation:
Topical antioxidants (e.g., vitamin C, glutathione) reduced ROS levels in IF-treated mice, partially restoring hair growth. This suggests targeted interventions may alleviate IF-related hair loss .
The study’s authors stress that their goal is not to demonize IF but to highlight its dual effects. While IF can aid weight loss and metabolic health, individuals must weigh these benefits against potential side effects, especially hair thinning in genetically predisposed populations. Key considerations include:
- Individual Variability: Hair loss risk may depend on genetics, fasting duration, and overall nutrition.
- Moderation: Shorter fasting windows (e.g., 12:12) or periodic fasting (2 days/week) might minimize stress on HFSCs.
- Antioxidant Support: Diets rich in fruits, vegetables, or supplements (e.g., N-acetylcysteine) could counteract oxidative damage during fasting .
As with any dietary intervention, consulting healthcare professionals is crucial, particularly for those with pre-existing hair conditions or nutritional deficiencies.
Conclusion
Intermittent fasting offers compelling benefits for metabolic health, but its impact on hair growth underscores the importance of a holistic approach to wellness. By understanding how IF influences both energy metabolism and tissue-specific stem cells, individuals can tailor fasting protocols to their goals while mitigating risks. Future research, including larger human trials, will further clarify IF’s long-term effects on hair and overall health.
References
1. Chen, H. et al. Intermittent fasting triggers interorgan communication to suppress hair follicle regeneration. Cell. 2025. DOI: https://www.cell.com/cell/abstract/S0092-8674(24)01311-4
2. Anton, S. D. et al. Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting. Obesity (Silver Spring). 2017. DOI: 10.1002/oby.22065
3. Imada, S. et al. Fasting can reduce weight — but also hair growth. Nature. 2024. DOI: https://doi.org/10.1038/d41586-024-04084-9
4. Mattson, M. P. et al. Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine. 2020. DOI: 10.1056/NEJMra1905136
