Human hairs sprout from follicles, which contain stem cells that are sensitive to dietary changes (artificially coloured).Credit: Dr Keith Wheeler/SPL
A popular weight-loss regimen stunts hair growth, data collected from mice and humans suggest1. The study’s findings show that intermittent fasting, which involves short bouts of food deprivation, triggers a stress response that can inhibit or even kill hair-follicle stem cells, which give rise to hair.
The results, published in today in Cell, suggest that although short-term fasting can provide health benefits, such as increased lifespan in mice, not all tissue and cell types benefit.
“I was shocked to hear these results,” says Ömer Yilmaz, a stem-cell biologist at the Massachusetts Institute of Technology in Cambridge who was not involved in the study. “We’ve come to expect that fasting is going to be beneficial for most, if not all cell types and good for stem cells. This is the inverse of what we expected, and the finding seems to hold true in humans.”
Deliberate deprivation
During the past decade, intermittent fasting has become one of the most popular dieting regimens; by one count, about 12% of adults in the United States practised it in 2023. One of the most common forms is time-restricted eating, which involves eating only within a limited time frame each day.
Stem cells seem to be particularly vulnerable to changes in diet. For example, Yilmaz and his colleagues reported2 in August that stem cells in the guts of mice showed a burst of activity during post-fast feasting. This activity helped to repair damage in the animals’ intestines.
To learn whether dieting affects hair regrowth, which can be affected by stress, Bing Zhang, a regenerative biologist at Westlake University in Zhejiang, China, and his colleagues shaved mice and subjected them to one of two intermittent-fasting regimens: time-restricted eating and alternate-day fasting, in which animals fasted for 24 hours and then ate their normal diet for the following 24 hours. By the end of the three-month study, the dieting mice had not regrown as much hair as control animals that ate a similar number of calories, the authors found.
Hair regrowth over roughly 100 days was much quicker in mice allowed to eat whenever they wanted (top row) than in mice allowed to eat for only 8 hours per day (middle) or mice allowed to eat only every other day (bottom row).Credit: H. Chen et al./Cell
The researchers traced this effect to the death of hair-follicle stem cells. Further experiments showed that intermittent fasting kick-started communication between the adrenal glands, organs that produce stress hormones, and fat cells in the skin. This crosstalk caused skin fat cells to release molecules called fatty acids. The fatty acids disrupted the stem cells’ metabolism and caused damage that, in some cases, led to the stem cells’ death. Application of an antioxidant cream before and during the diet prevented stunting of hair growth, suggesting that this effect is not inevitable.
