Intermittent Fasting Can Lead To This Unwanted Side Effect

Intermittent fasting has gained attention for its potential benefits, such as improving metabolic health and supporting weight loss. However, a recent study suggests that this eating pattern might have an unintended side effect—slowing down hair growth.

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Published on Dec. 13 in Cell Press, the study conducted by researchers from Westlake University in Zhejiang, China, examined the effects of intermittent fasting on hair regeneration. The team found that while fasting improved metabolic health in mice, it also led to slower hair regrowth compared to mice that had constant access to food. The same results were observed in a small clinical trial involving human participants.

Lead researcher Bing Zhang and his team focused on how fasting might impact skin and hair cells—a topic that had not been explored in depth before. To investigate, they shaved a group of mice and subjected them to various fasting regimens. Some mice were on a time-restricted feeding (TRF) schedule, eating for eight hours each day and fasting for the remaining 16 hours, while others followed an alternate-day feeding (ADF) pattern.

The findings were striking. After 96 days, the mice on both intermittent fasting schedules had only partial hair regrowth while mice with unrestricted access to food regrew most of their fur within just 30 days. The researchers were surprised by this slower rate of hair regrowth under fasting conditions.

Further analysis revealed that intermittent fasting appears to selectively reduce the activity of hair follicle stem cells (HFSCs), which are crucial for hair regeneration. This reduction in stem cell activity may be the reason for the delayed hair growth observed in the fasting mice.

“We don’t want to scare people away from practicing intermittent fasting because it is associated with a lot of beneficial effects — it’s just important to be aware that it might have some unintended effects,” Zhang said of the findings. 

The mice who had trouble regrowing hair experienced cell death in their hair follicles, the study noted.

In the mice that experienced slower hair regrowth, researchers discovered that the activated hair follicle stem cells (HFSCs) underwent apoptosis (programmed cell death) during prolonged fasting periods. Through genetic engineering techniques, the team identified that this fasting-induced cell death was linked to elevated levels of free fatty acids near the hair follicles. According to Zhang, these fatty acids triggered the accumulation of harmful reactive oxygen species (ROS) within the HFSCs, leading to their apoptosis. In lab tests, they also observed that free fatty acids caused human HFSCs to undergo apoptosis in vitro, further confirming the mechanism at play.

“During fasting, adipose tissue starts to release free fatty acids, and these fatty acids enter the HFSCs that were recently activated, but these stem cells don’t have the right machinery to use them,” Zhang added. 

While intermittent fasting may slow down hair regeneration, it offers several health benefits.

According to Healthline, intermittent fasting can help lower blood pressure, improve insulin sensitivity, and reduce cholesterol levels. A 2009 study of 16 obese men and women found that intermittent fasting led to a 6% reduction in blood pressure over just eight weeks. The same study also showed significant reductions in LDL cholesterol (down 25%) and triglycerides (down 32%), contributing to weight loss.

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For women, intermittent fasting may also positively impact menstrual health. A small 2021 study examined 18 women aged 18-31 with PCOS over six weeks. Participants saw notable improvements in menstrual cycle regularity and reductions in body fat, along with other health benefits. However, women should approach intermittent fasting with caution, as prolonged fasting may disrupt hormonal balance, according to registered dietitian Julia Zumpano.

“Fasting can make estrogen and progesterone take a nose-dive,” Zumpano told the Cleveland Clinic. 

Estrogen and progesterone levels fluctuate throughout your menstrual cycle, and this hormonal regulation is largely controlled by gonadotropin-releasing hormone (GnRH). However, GnRH is highly sensitive to environmental factors, and practices like fasting can interfere with its ability to release the necessary signals for stimulating estrogen and progesterone production. When these hormone levels drop, it can lead to a range of symptoms, such as changes in your menstrual cycle, including missed periods, as well as increased mood swings, irritability, hot flashes, night sweats, headaches, and even heart palpitations.

So, it’s important to proceed with caution and be mindful when adopting this unique eating method.

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