Fasting-Mimicking Diet Shows Encouraging Trends for Male Fertility: 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


Title	Fasting for male fertility—a mixed methods study
Journal	Frontiers in Nutrition
Published	January 2025
Study type	Two-arm randomized controlled exploratory trial (mixed methods)
Total participants	18 completers (10 fasting, 8 control)
Duration	4 months of fasting cycles, sperm parameters assessed at baseline and 6 months
Lead researcher	Katharina T. May
Institution	Not reported in accessible abstract
Funding	Not reported
Note	PubMed and journal full-text access were blocked by a network restriction in the remote research environment this run; figures below were verified through indexed abstract summaries rather than the full PDF
Source	View on PubMed →

What This Study Looked At

Male fertility research has mostly focused on diet quality, weight, and lifestyle factors, leaving open the question of whether structured fasting protocols could meaningfully help. This pilot study set out to test whether a fasting-mimicking diet — a very-low-calorie protocol designed to trigger fasting-like metabolic effects while still providing minimal food — could improve semen quality in men who already had impaired sperm parameters, while also gathering qualitative feedback on whether the protocol was realistic to sustain alongside a full-time job.

Who Was Studied

Group	Participants	What They Did
Fasting group	10 men (completers)	Followed a fasting-mimicking diet (approximately 500 kcal/day) for 5 consecutive days, repeated three times across 4 months
Control group	8 men (completers)	Instructed to maintain their usual lifestyle and diet, assessed on a waiting-list basis

Participant profile: Men with impaired sperm quality; fasting group averaged 36.9 years (± 5.17), control group averaged 36.1 years (± 2.8). A subgroup also took part in semi-structured qualitative interviews about their experience with the protocol.

How the fasting-mimicking diet worked: Participants in the fasting arm ate a low-calorie, plant-based meal plan of roughly 500 kcal per day for five consecutive days, repeating this cycle three separate times over four months, while the control group changed nothing about their normal routine.

What the Researchers Found

Sperm Parameters: Small, Favorable Trends

Measure	Result (fasting vs. control)
Total sperm motility	Small positive trend favoring fasting (η² = 0.030)
Progressive sperm motility	Small-to-moderate positive trend favoring fasting (η² = 0.059)
Total sperm count	Negligible positive trend favoring fasting (η² = 0.001)
Sperm concentration	Small positive trend favoring fasting (η² = 0.050)
Normal sperm morphology	Small positive trend favoring fasting (η² = 0.019)
Percentage of round cells	Larger trend favoring fasting (η² = 0.462)

None of these differences reached statistical significance given the very small sample size (18 completers), but every WHO-standard semen parameter measured showed a trend in favor of the fasting group compared to the control group, which generally trended downward over the same period.
Semen quality was assessed using standard World Health Organization criteria: motility, concentration, total count, ejaculate volume, and morphology.

The Feasibility Question

Qualitative interviews with a subgroup of participants found the fasting-mimicking protocol was feasible to follow and compatible with continuing full-time work — an important practical finding for a lifestyle intervention aimed at everyday men, not just people with flexible schedules.

What Did Not Change

No statistically significant between-group differences were found for any individual semen parameter — this was a small pilot study, not a definitive efficacy trial.

What the Researchers Concluded

The authors concluded that while no parameter reached statistical significance between groups, the consistent direction of the trends — all favoring the fasting group — combined with positive feasibility findings, supports running a larger, adequately powered trial to properly test whether fasting-mimicking diets can meaningfully improve male fertility markers.

What This Means If You Fast

This is early, exploratory evidence — not proof. With only 18 completers, this study wasn't statistically equipped to detect real effects; treat the positive trends as a reason for further research, not a guarantee.
The pattern is consistent, even if small. Every single sperm parameter measured moved in the same favorable direction for the fasting group, which is a meaningful signal even without statistical significance.
A fasting-mimicking diet is a specific, structured protocol — very low daily calories for a defined stretch of days, repeated periodically — rather than standard daily time-restricted eating like 16:8. Results here may not generalize directly to daily eating-window fasting.
Feasibility matters for real-world use. The finding that participants could maintain the protocol alongside full-time work is practically important for anyone considering a similar approach.
Men trying to conceive should loop in a doctor first, particularly given how many other lifestyle and medical factors affect fertility — fasting is one variable among many.
This connects to broader fasting-mimicking research, including work on IGF-1 and metabolic aging markers, suggesting overlapping hormonal mechanisms may be at play.

Study Limitations

Extremely small sample size (18 completers total, 10 in the fasting arm), which severely limits statistical power and the ability to detect true effects.
No statistically significant results were found for any outcome — all findings are described as "trends," not confirmed effects.
The study was explicitly exploratory and described by its own authors as a pilot for a larger future trial.
Baseline sperm impairment level and underlying causes of infertility in participants were not detailed in the accessible abstract, limiting how broadly the findings can be applied.
Full-text verification of exact statistical methods and effect size confidence intervals was limited by a network access restriction in the environment this article was written in; figures were confirmed against indexed abstract summaries rather than the complete published dataset.

Source

May, K. T., et al. (2025). Fasting for male fertility—a mixed methods study. Frontiers in Nutrition. PMID: 39885870

Frequently Asked Questions

Does intermittent fasting improve sperm quality?

This small pilot study found positive trends across every sperm parameter measured (motility, concentration, count, and morphology) in men following a fasting-mimicking diet, but none reached statistical significance due to the very small sample size. It's an encouraging early signal rather than confirmed proof.

What is a fasting-mimicking diet?

A fasting-mimicking diet (FMD) is a structured, very-low-calorie eating protocol — in this study, around 500 kcal per day for five consecutive days — designed to trigger many of the metabolic effects of fasting while still providing minimal nutrition, typically repeated in periodic cycles.

Is this the same as daily intermittent fasting like 16:8?

No. This study used a fasting-mimicking diet done in five-day cycles three times over four months, which is quite different from daily time-restricted eating protocols like 16:8. The findings shouldn't be assumed to apply directly to daily eating-window fasting.

Can men realistically follow a fasting-mimicking diet while working full-time?

Based on qualitative interviews in this study, yes — participants reported the protocol was feasible and compatible with continuing full-time work, which is a practically useful finding for anyone considering trying it.

Should men trying to conceive try fasting to improve fertility?

This study is too small and preliminary to recommend fasting as a fertility treatment on its own. Men trying to conceive, especially with existing sperm quality concerns, should talk to a doctor or fertility specialist before making significant dietary changes.

Fasting-Mimicking Diet Shows Encouraging Trends for Male Fertility: What the Research Shows