You fast 16 hours a day for your fitness, your blood sugar, or simply because it fits your schedule. Millions of men now do it, from athletes to office workers who skip breakfast. But early this year, a study published in the scientific journal Cell raised a less pleasant question: can fasting slow down your hair growth?
We previously wrote that intermittent fasting in itself does not have to be a problem for your hair, as long as you get enough calories within your eating window. This still largely holds true, but the new study uncovers a mechanism that is independent of how much you eat. Below, you can read what exactly was found, and what you can do with that information.
What the study did
Researchers from Peking University published their findings in January 2025 in Cell. They subjected mice to common fasting regimens, including a pattern similar to 16:8, and monitored what happened to their hair follicles after their fur was shaved.
The mice that fasted regrew their fur significantly slower than the mice that could eat normally. After ninety days, the fasting mice had only partially regrown their fur, while the control group had largely recovered within thirty days.
To check if this also applies to humans, the researchers then followed a group of healthy adults who fasted eighteen hours a day. Their hair growth rate was, on average, 18 percent lower afterward than in a group that ate normally. This was a relatively small study, but the direction of the effect was consistent with what they observed in mice.
The mechanism: free fatty acids under pressure
So there was an effect. What makes the study truly worthwhile is how that effect arises. The researchers expected fasting to work through the known pathway: fewer calories, fewer building blocks, slower recovery. That turned out not to be the explanation.
What they found was a communication between your adrenal glands and the adipose tissue under your skin. During a fasting period, your body switches from glucose to fat as fuel. This releases free fatty acids from the fat cells around your hair follicles. In small amounts, this is not a problem, but with the fasting regimens studied, these fatty acids were released in a peak, directly into the immediate vicinity of the hair follicle stem cells.
These stem cells are the engine behind new hair growth. They appeared to have difficulty processing the sudden wave of free fatty acids. The result was oxidative damage and, in some cells, cell death. Less active stem cells mean a slower hair cycle.
What this study also showed: the effect was independent of calorie restriction, independent of your biorhythm, and independent of the known mTORC1 pathway that much nutritional research typically delves into. It was specifically the timing and the peak in free fatty acids that made the difference, not how much you ate in total.
Does this mean fasting is bad for your hair?
Not by definition, and certainly not as an established fact for everyone. A few things to put into perspective.
It is an animal study with an additional human experiment of limited scope. Eighteen percent slower hair growth is measurable, but it's not baldness, and it doesn't say anything about what happens if you eat normally again after a few months. In the mice, recovery did occur, just more slowly.
The study looked at hair growth rate, not whether your hair actually falls out. Slower growing hair follicles are different from follicles that stop growing or miniaturize, as is the case with hereditary hair loss. If you are already sensitive to DHT, it is plausible that an extra brake on your hair cycle does not help, but it has not been shown that fasting causes or accelerates hereditary hair loss in the same way that DHT does.
Who is this relevant for?
Especially for men who are already noticing their hair thinning and who also follow a strict fasting regimen, such as OMAD (one meal a day) or a longer window than 16:8. The longer and stricter the fasting pattern, the larger the peak in free fatty acids is likely to be.
For men without visible hair loss who occasionally stick to a 16:8 schedule, it's unlikely that this will make a noticeable difference. Your hair follicles will then experience relatively few of these peaks, and your normal eating pattern during the other hours of the day probably compensates for some of the pressure.
What you can do if you still want to fast
You don't have to stop immediately if you benefit from intermittent fasting for your weight or blood values. A few adjustments that make sense according to the logic of this research are:
- Keep your fasting window short. 14:10 or 16:8 gives your body less time to build up large peaks of free fatty acids than 20:4 or OMAD.
- Eat enough protein and healthy fats within your eating window, so your body doesn't have to rely extra on its own fat reserves.
- Build in pause days if you notice your hair thinning. A few days of normal eating per week can relieve the pressure on your hair follicles without completely abandoning your fasting routine.
- Do not combine strict fasting with a low-calorie diet. These two things together put extra pressure on your body, and we have already written that crash diets can trigger telogen effluvium.
Can a serum counteract this mechanism?
Not directly. A serum does not interfere with the free fatty acids in your adipose tissue or the communication between your adrenal glands and your skin. That is an internal process that you mainly address with your fasting schedule itself.
What a serum can help with is supporting the hair follicle itself when it is under extra pressure. The Hairborn Growth Serum contains, among other things, Redensyl and caffeine, which stimulate blood circulation to the scalp and support the growth phase of your hair. This does not change what happens in your adipose tissue during fasting, but it can help keep your hair follicles in a better starting position. If you use a derma roller with it, maintain the usual ten hours between rolling and applying serum for the best results.
In short
A study from Cell (January 2025) showed that intermittent fasting in mice and, to a lesser extent, in humans can slow down hair growth. The cause lies in a peak of free fatty acids around the hair follicle stem cells during fasting, regardless of how many calories you eat. This concerns delayed growth, not proven baldness, and the effect appears to be greater with stricter regimens such as OMAD than with a moderate 16:8 pattern. If you notice your hair is already thinning, a shorter fasting window or an occasional pause day is a reasonable precautionary measure.
Frequently asked questions
Does intermittent fasting cause hair loss?
Intermittent fasting does not cause hair loss in the sense of bald spots, but according to a study from Cell (2025), it can slow down your hair growth rate. In mice, fasting caused a peak in free fatty acids around the hair follicle stem cells, which significantly slowed hair growth after shaving. In humans, the effect was smaller: an average of 18 percent slower hair growth with eighteen hours of fasting per day.
Was this research only done on mice, or also on humans?
The research was done on both. The main experiment was on mice, where fasting noticeably slowed hair growth after shaving due to damage to hair follicle stem cells. The researchers then also tested the effect on a small group of healthy adults who fasted eighteen hours a day, and observed a similar, slightly smaller delay in hair growth rate there.
Does it matter if I fast 16:8 or for a longer period like OMAD?
Probably, although this was not tested one-to-one in the study. The longer and stricter your fasting window, the greater the peak in free fatty acids around your hair follicles is likely to be, because your body relies on fat burning for longer. A moderate regimen like 16:8 gives your body more hours per day to stay outside that peak than OMAD or a window of twenty hours or more.
Will my hair growth recover if I stop fasting?
In the mice in the study, hair growth did recover, just slower than in the control group that had never fasted. There is no reason to assume that the effect in humans is permanent, as the mechanism revolves around temporary damage to stem cells during an active fasting period. As soon as you eat normally again, your hair follicles get a chance to recover.
Does the number of calories I eat play a role, apart from fasting?
No, that's precisely what's striking about this study. The researchers explicitly ruled out calorie restriction as an explanation and found that the effect was mainly due to the timing of eating and the associated peak in free fatty acids, not the total amount of calories. So you can eat enough and still trigger this mechanism, purely by the way you distribute your meals throughout the day.
Is this the same mechanism as with crash diets or extreme weight loss?
No, it's a different mechanism, although both can lead to increased hair loss. Crash diets and rapid weight loss are mainly associated with telogen effluvium, where hair follicles massively enter the resting phase due to a lack of calories or building blocks. The mechanism from the fasting study works through free fatty acids that damage hair follicle stem cells, regardless of whether you eat enough in total.
Should I stop intermittent fasting if I already have thinning hair?
Not necessarily, but it is a reason to critically review your schedule. Consider a shorter fasting window, such as 14:10 instead of 16:8 or OMAD, and possibly include days without fasting. If your hair loss is already clearly visible, it is in any case wise to have the underlying cause checked before blaming everything on your diet.
What are free fatty acids and why are they relevant to my hair follicles?
Free fatty acids are fat molecules that are released from your fat cells when your body switches from glucose to fat as fuel, which happens during fasting. Around your hair follicles, these fatty acids can increase sharply in a short time, and the stem cells that drive new hair growth appeared to have difficulty processing that peak in the study. This led to oxidative damage and some of the stem cells were lost as a result.
Does this also apply to longer fasting periods such as 24 hours or more?
The study primarily tested regimens around eighteen hours, so less is directly known about longer periods such as 24 hours or multi-day fasting. Based on the mechanism, a peak in free fatty acids that lasts longer the longer you fast, it is plausible that longer fasting periods are more likely to have a greater effect. Hard evidence for those specific regimens is currently still lacking.
Can a hair serum compensate for the effects of fasting on my hair follicles?
A serum does not intervene in the free fatty acids or the underlying communication between your adrenal glands and adipose tissue, so it does not counteract the mechanism itself. What a serum with Redensyl and caffeine, such as the Hairborn Growth Serum, can do is support blood flow to your scalp and stimulate the growth phase of existing follicles. View it as external support, not as a solution to what happens internally during fasting.
