Intermittent Fasting Slowed Hair Regrowth by 18% in a Small Human Trial: What the Research Shows

Intermittent Fasting Slowed Hair Regrowth by 18% in a Small Human Trial: What the Research Shows

Medical disclaimer: This article summarises published research for informational purposes only. It is not medical advice and is not a substitute for guidance from a qualified health professional. Always consult your doctor before starting any fasting protocol, especially if you have an existing health condition or take medication.

Study at a Glance

What This Study Looked At

Researchers set out to understand how intermittent fasting affects hair follicle stem cells — the cells responsible for regrowing hair. The bulk of the study was conducted in mice, but the team also ran a small randomized clinical trial in humans to check whether the same effect on hair regrowth speed shows up outside of a mouse model. If you're curious how fasting interacts with other visible signs of aging, see fasting and hair regrowth in women.

Who Was Studied

Participant profile: 49 healthy young adults, split across the three groups described above.

How the 18:6 protocol worked in this study: Participants in the time-restricted eating group confined all eating to a 6-hour daily window and fasted for the remaining 18 hours, for the roughly 10–12 day study period.

Researchers shaved a small patch of scalp on each participant at the start of the trial and tracked how quickly hair regrew in that patch over the study period, using this as the primary measure of hair follicle activity.

What the Researchers Found

Hair Regrowth Speed

• The time-restricted eating group showed an 18% reduction in the speed of hair regrowth on the shaved scalp patch compared with the control group.
• Regrown hairs in the fasting group tended to be thinner in diameter than those in the control group.

What Did Not Change

• Overall hair shaft density did not show a significant difference between groups — the effect showed up in regrowth speed and hair thickness, not in the number of hairs present.

The Proposed Mechanism (From the Mouse Data)

The mouse portion of the study found that intermittent fasting triggers communication between the adrenal glands and adipocytes (fat cells) in the skin, causing a rapid release of free fatty acids into the tissue surrounding hair follicles. This raised oxidative stress (reactive oxygen species) in activated hair follicle stem cells, leading to cell damage and, in mice, apoptosis (cell death) of a portion of those stem cells. The researchers propose this same interorgan signaling pathway, acting more mildly, explains the slower regrowth and thinner hair seen in the human fasting group — since humans have a much lower metabolic rate than mice, the effect on hair follicle stem cells was correspondingly milder.

What the Researchers Concluded

The authors concluded that commonly used intermittent fasting regimens can inhibit hair follicle regeneration, primarily through oxidative damage to activated hair follicle stem cells driven by fasting-triggered fat-cell signaling — and that while this effect is severe in mice, it appears as a milder, measurable slowing of hair regrowth speed in humans.

What This Means If You Fast

• A modest effect, not hair loss. The human data showed slower regrowth and thinner hairs over a 10–12 day window — this is not the same as hair falling out, and overall hair density was unchanged.
• Mice are not humans. The dramatic stem-cell apoptosis seen in mice does not translate one-to-one to people; the researchers themselves note the effect in humans was substantially milder, likely because of humans' slower metabolic rate.
• Timing may matter if you're actively regrowing hair. If you're recovering from postpartum shedding, treating hair loss, or otherwise prioritizing hair regrowth right now, it may be worth discussing your fasting schedule with a doctor or dermatologist. See does fasting improve skin for women? for a related discussion of fasting's visible effects.
• This is one short-term study. Ten to twelve days is a small fraction of a normal hair growth cycle, which runs over months — long-term effects on actual hair loss or thickness remain unknown.
• It doesn't cancel out fasting's other evidence. This finding sits alongside a large body of research on fasting and metabolic health; it's a data point on one specific outcome, not a reason to abandon intermittent fasting broadly.

Study Limitations

• The core mechanistic findings come from mice, not humans — the human data is a smaller, secondary confirmatory arm within the same paper.
• The human sample size was small (49 participants split across three groups) and the study ran for only about 10–12 days.
• Hair regrowth was measured on a single shaved scalp patch, which may not reflect real-world, whole-scalp hair loss or thinning.
• The study population was drawn from a single research center in China; effects may vary across different ages, hair types, and health backgrounds.
• No long-term follow-up was reported, so whether the slower regrowth persists, reverses, or compounds over months of sustained fasting is unknown.

Source

Chen H, Liu C, Cui S, et al. (2024). Intermittent fasting triggers interorgan communication to suppress hair follicle regeneration. Cell. PMID: 39674178

Frequently Asked Questions

Does intermittent fasting cause hair loss?

Not according to this study — hair shaft density was unchanged. What the researchers found was slower hair regrowth and thinner regrown hairs, not hairs falling out.

How much does intermittent fasting slow hair growth?

In this trial, the 18:6 time-restricted eating group regrew hair about 18% slower than the control group over roughly 10–12 days.

Is intermittent fasting hair thinning permanent?

The study didn't test this — it only tracked regrowth over about 10–12 days. Whether the effect persists, reverses, or builds up over months of sustained fasting is unknown.

Why does fasting affect hair follicles at all?

The mouse data suggests fasting triggers a chain reaction between the adrenal glands and fat cells in the skin, releasing free fatty acids near hair follicles that raise oxidative stress in the stem cells responsible for regrowth.

Should I stop intermittent fasting if I'm worried about hair thinning?

This single small study isn't a reason to stop fasting on its own, but if you're actively working on hair regrowth or noticing thinning, it's worth raising with a doctor or dermatologist who can look at your specific situation.

Related Research and Articles

• Fasting and hair regrowth in women
• Intermittent fasting and hair loss in women
• Fasting and collagen production in women's skin
• Iron levels and intermittent fasting for women
• The biggest intermittent fasting myths, debunked

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