Intermittent fasting leaves us hairless

The researchers of the Westlake University in Zhejian (China), to determine if the same thing happened in humans, they carried out a small clinical trial with 49 healthy young adults. Thus, they showed that a time-restricted diet involving 18 hours of fasting per day reduced the average speed of hair growth by 18% compared to controls, but larger studies are needed to verify this effect given the small size of the study sample and its short duration (10 days).

“We don’t want to scare people away from intermittent fasting because it is associated with many beneficial effects; It’s just important to note that it may have some unwanted effects,” says lead author and stem cell biologist Bing Zhang.

In addition to its metabolic benefits, previous studies have shown that fasting can improve the stress resistance of stem cells associated with blood, intestinal and muscle tissue, but little is known about how it affects peripheral tissues such as skin and hair. .

Zhang’s team hypothesized that fasting might also be beneficial for skin tissue regeneration, the process by which old, damaged cells are replaced.

To test this, they examined hair growth in mice that had been shaved and subjected to different intermittent fasting regimens. Some mice were fed a time-restricted feeding (TRF) schedule involving 8 hours of food access and 16 hours of fasting each day, while other mice were subjected to alternate-day feeding. .

HE surprised upon discovering that fasting inhibited hair regeneration. While control mice that had unlimited access to food had regained most of their hair after 30 days, mice that followed both intermittent fasting regimens showed only partial hair growth after 96 days.

Stress

The team showed that this inhibition of hair growth occurs because hair follicle stem cells (HFSCs) cannot cope with the oxidative stress associated with the switch from glucose to fat use. HFSCs go through phases of activity and inactivity, and hair growth depends on these cells becoming activated. While HFSCs from control mice began to activate around day 20 after shaving and remained active until their hair grew back, activated HFSCs from intermittent fasting mice underwent apoptosis (programmed cell death) for prolonged periods. fasting

Using genetic engineering methods, the team showed that this fasting-induced apoptosis was driven by an increased concentration of free fatty acids near the hair follicles, causing an accumulation of harmful oxygen radical species within the HFSCs. Free fatty acids also caused human HFSCs to undergo apoptosis in vitro.

“During fasting, adipose tissue begins to release free fatty acids, and these fatty acids enter the HFSCs that have recently been activated, but these stem cells do not have the proper machinery to use them,” says Zhang.

In comparison, epidermal stem cells, which are responsible for maintaining the epidermal skin barrier, were not affected by intermittent fasting. The main difference between these types of stem cells is that epidermal stem cells have a greater antioxidant capacity. When the team tested whether antioxidants could mitigate the effects of fasting on hair growth, they showed that both topical application of vitamin E and genetic upregulation of antioxidant capacity helped high-fructose stem cells survive fasting.

“The human population is very heterogeneous, so the effects may be different for different people,” says Zhang. Mice also have a very high metabolic rate compared to humans.so fasting and metabolic change have a more severe effect on mouse HFSCs. We see a milder effect in humans: there are still apoptotic stem cells, but many HFSCs survive. Therefore, there is still hair regrowth; “It’s just a little slower than usual.”

In future work, the researchers plan to collaborate with local hospitals to investigate how fasting affects other types of stem cells in the skin and other body systems.