The effect of obesity interventions on male fertility: a systematic review and meta-analysis

Losing weight may help sperm quality, but the method matters—and most of the evidence is weak

Journal: Human Reproduction Update | Published: 2026-03-01 | Type: Systematic Review, Meta-Analysis | PMID: 41065428 Authors: Peel A, Lyons H, Tully CA, Vincent AD, Jesudason D, Wittert G, McPherson NO (Freemason Centre of Male Health and Wellbeing / Robinson Research Institute, University of Adelaide) Funding/COI: Not disclosed

Summary

This systematic review pooled 32 studies examining whether obesity interventions—lifestyle changes, pharmacotherapy, or bariatric surgery—improve semen quality or fertility outcomes in men with obesity. The headline finding is a split verdict: lifestyle interventions (diet and exercise) showed modest improvements in sperm morphology and progressive motility in pre-post analyses, while bariatric surgery produced no clinically meaningful changes despite more drastic weight loss. Pharmacotherapy data (metformin, liraglutide) were too sparse to evaluate. The authors themselves rate the certainty of evidence as low across nearly all modalities.

Claims

• Lifestyle interventions (10 studies, 5 RCTs): fixed-effect meta-analysis found improvements in normal sperm morphology (mean difference +0.59%, 95% CI [0.23, 0.94]) and progressive motility (+10.56% [8.97, 12.15]) in pre-post analyses
• Bariatric surgery (18 studies, 1 RCT): random-effects meta-analysis of pre-post outcomes found no clinically significant changes in semen parameters or sperm DNA damage
• RCT-specific finding: fixed- and random-effects meta-analysis of RCTs only found no differences in sperm parameters between intervention and control arms across any intervention modality
• Pharmacotherapy (5 studies): insufficient data to draw conclusions on metformin or liraglutide effects on fertility
• Conception rates and assisted reproduction outcomes were "limited across all modalities"—virtually no studies measured the outcome that actually matters

Study Quality

This is a well-conducted systematic review with pre-registered protocol (PROSPERO CRD42022349665) and broad multi-database search through December 2024. The authors are appropriately conservative about their findings, explicitly rating evidence certainty as low and conducting both fixed- and random-effects models. The decision to separate RCT-derived estimates from pre-post quasi-experimental data is methodologically sound—and that separation is where the review quietly buries its most important finding.

The lifestyle intervention improvements come from pre-post analyses, not from the RCT comparison arms. When the authors ran RCT-only meta-analyses, no intervention showed a statistically significant difference from control. Pre-post designs cannot rule out regression to the mean, seasonal variation in semen quality, or the Hawthorne effect. The 0.59% improvement in normal morphology, while statistically significant by confidence interval, is also clinically small—Kruger strict criteria set normal morphology at ≥4%, making a 0.59% shift of uncertain reproductive consequence.

Red Flags

• The RCT evidence—the most reliable signal here—showed no effect from any intervention; the lifestyle improvements are pre-post artifact candidates
• 12 of 18 bariatric surgery studies were quasi-experimental; the sole bariatric RCT had a sample size that "limits interpretability" (their words)
• Conception rates and live birth rates—the outcomes patients actually care about—were measured in almost no studies; semen analysis is a surrogate, not an endpoint
• Funding and conflicts of interest are not disclosed for this paper, which is a reporting failure for a review published in a flagship reproductive medicine journal
• GLP-1 agonists (the current dominant obesity pharmacotherapy) are barely represented—the review mostly captures metformin and liraglutide, with the review authors themselves flagging the GLP-1 data gap
• Included studies span a wide heterogeneity of interventions, populations, and follow-up durations, limiting comparability

Strengths

• Pre-registered protocol with broad search across five databases
• Methodologically honest: authors explicitly label evidence certainty as low and distinguish RCT from pre-post findings
• Meta-regression attempted to assess dose-response (weight lost vs. semen improvement) where data allowed
• Covers all major intervention modalities in one review, mapping the full evidence gap
• Identifies concrete research priorities: RCTs measuring conception rates, GLP-1 agonist studies, adequate follow-up durations

Verdict

Read this review to understand what we don't know about obesity and male fertility, not what we do. The RCT evidence—which actually controls for confounding—showed no intervention moved sperm parameters significantly. The lifestyle improvements that generate the optimistic framing in the abstract come from pre-post designs that can't rule out natural variation. Bariatric surgery producing no benefit despite massive weight loss is genuinely interesting and suggests the sperm damage from obesity isn't purely mediated by adiposity. The methodological transparency here is commendable, but the evidence base it summarizes is thin, quasi-experimental, and focused on surrogates. A well-designed multicenter RCT measuring live birth rates is what this field needs; this review confirms no one has done it yet.