Eat less to live longer… but with less hair? This is the difficult choice that could be faced by all those who wish to improve their health by following an intermittent fast. Several studies, notably in animal models, have shown that this approach of food restriction, where one only eats for a few hours of the day, could be beneficial. It would protect the heart, and could decrease the risk of metabolic diseases.
However, a new study has just shown that intermittent fasting could also have less desirable effects… particularly for hair. Researchers from Zheijang University in China have shown in mice and humans that this dietary restriction affects follicular stem cells, considerably slowing down the hair regrowth. These results were published on December 13, 2024 in the journal Cellular.
Hair regrowth is disrupted due to dietary restriction
To find out if intermittent fasting could have any impact on hair regrowth, the researchers shaved mice and then fed them two types of food restriction: intermittent fasting, where the mice had access to food for only eight hours, and were required to fast for the remaining 16 hours; total fasting every other day; and a control group with a normal diet (ad libitum). Thirty days after being shaved, the normally fed mice had already regained most of their hair. But this was not the case for the other two groups. Worse: after three months, their hair still had not grown back completely.
To find out if this effect also occurred in humans, the authors analyzed the impact of intermittent fasting in 49 healthy adults, who had to fast for 18 hours every day, for 10 days. In them, hair regrowth slowed by about 18 % compared to participants without any dietary restrictions. Confirming that intermittent fasting also has repercussions on human capillarity, even if they seem less than those observed in mice.
Activation of hair stem cells depends on their environment
Hair regeneration occurs during the third phase of the hair life cycle. During this phase, called telogen, the old hair breaks off and falls out, and is then replaced by a new hair follicle, which will produce a new hair during the first phase, called anagen. This requires the activation of a follicular stem cell. The activation of these stem cells depends in part on its cellular environment, which can change depending on the physiology of the individual.
However, diet can cause physiological changes and therefore have an impact on the activation of these follicular stem cells. Indeed, the authors have shown that these two types of dietary restriction (fasting for a few hours and fasting every other day) lead to the release of fatty acids by the skin's fat cells. Because, subjected to the stress caused by the lack of food, the metabolism adapts by burning more of its fat reserves. But some of this fat then accumulates around the follicular stem cells, modifying their environment.
This change in the environment of cells causes oxidative stress
This accumulation of fatty acids resulted in an increase in oxidative stress in these stem cells, causing more cell death. But this loss of hair cells is not inevitable. The authors of this work managed to avoid it by increasing the antioxidant defenses of these cells. Importantly, enhancing the antioxidant capabilities of follicular stem cells may significantly decrease the inhibitory effect of intermittent fasting on follicle regeneration, which could help find ways to avoid this impact on human hair regrowth.", the authors say. Until we figure out how to reduce this oxidative stress, your hair may be paying the price for the fast.