Does Diet Really Affect Fertility?

What the research actually found

The most quoted evidence comes from the Nurses' Health Study II, which followed more than 17,000 women trying to conceive over eight years. Women whose eating and lifestyle habits most closely matched what the researchers called a "fertility diet" pattern had a substantially lower risk of infertility caused by ovulation problems. ^[1]

That pattern was not exotic. It meant more monounsaturated fat and less trans fat, more protein from plants than from red meat, a lower glycaemic load, more full-fat rather than low-fat dairy, adequate iron, a multivitamin containing folic acid, and a healthy body weight with regular movement.

Two things matter here. First, this was an observational study, so it shows an association rather than proof that the diet caused the improvement. Second, it applied specifically to ovulatory infertility, which is only one cause among many. Diet was never shown to fix tubal, structural, or genetic causes.

The clearest single finding: trans fats and ovulation

If one dietary factor stands out, it is trans fat. In the same cohort, replacing just 2% of daily energy from carbohydrate with trans fat was associated with a 73% higher risk of ovulatory infertility. ^[2] That is a large signal from a small dietary change, and it is one of the few nutrition findings in this field that is genuinely striking.

Industrial trans fats are far less common in Sweden than they once were, but they still turn up in some fried foods, commercial baked goods, and certain processed snacks. Cutting them is one of the few pieces of fertility nutrition advice with real weight behind it.

Weight, insulin, and why ovulation stalls

Ovulation is exquisitely sensitive to metabolic signals. When insulin runs persistently high, the ovaries produce more androgens, which can disrupt the maturation and release of an egg. This is the central mechanism in PCOS, the most common cause of ovulation problems in women of reproductive age.

A 2024 systematic review and network meta-analysis of women with overweight or obesity found that combining exercise with dietary change was the most effective strategy for improving ovulation, lowering BMI, and improving the hormonal profile. ^[3] Worth noting: the strongest effects came from combined approaches, and the outcomes measured were ovulation and hormones, not live birth rates.

Being significantly underweight, or eating too little relative to training load, suppresses ovulation just as reliably. Fertility nutrition is not about eating less. It is about eating enough, and eating in a way that keeps blood sugar and insulin steady.

• Steady blood sugar beats restriction. Build meals around protein, fibre, and fat rather than cutting carbohydrates out.
• Under-eating stops ovulation too. Low energy availability is a common and under-recognised cause of missing periods.
• Modest weight change can be enough. Ovulation often returns before a goal weight is reached.
• For the mechanism in depth, see my guide to insulin resistance, weight, energy, and hormones.
• If you have PCOS, my article on why PCOS is being renamed PMOS explains what the diagnosis really describes.

Fertility is not only a woman's issue

Roughly half of fertility problems involve a male factor, and diet shows up in that research too. A systematic review of observational studies found that eating patterns rich in omega-3 fats, antioxidants such as vitamin C, vitamin E, selenium, zinc, and folate, and low in saturated and trans fats, were associated with better semen quality. ^[4]

One mechanism is oxidative stress, which can damage the DNA carried inside sperm. Sperm DNA fragmentation can affect conception, IVF success, and recurrent miscarriage even when a standard semen analysis looks completely normal. You can read more about this in Herafem's article on sperm DNA fragmentation.

A word of caution on supplements. A 2022 Cochrane review of antioxidants for male subfertility found the evidence too uncertain to draw firm conclusions: it may improve live birth and pregnancy rates, but the studies carried a serious risk of bias. ^[5] Antioxidant-rich food is a reasonable bet. Expensive antioxidant supplements are not a proven treatment.

What diet cannot fix

This is the part most fertility nutrition content leaves out. No diet will unblock a fallopian tube, reverse severe endometriosis, restore diminished ovarian reserve, or correct a chromosomal problem. Nutrition improves the terrain. It does not rebuild the anatomy.

If you are under 35 and have been trying for a year, or over 35 and have been trying for six months, that is the point to get a medical assessment rather than a new eating plan. The same applies at any age if your periods are irregular or absent, if you have had recurrent miscarriages, or if you suspect endometriosis or PCOS.

A medical assessment typically includes blood work, a review of your cycle, and, where relevant, a semen analysis for your partner. Medical investigation and nutrition work well side by side, and neither replaces the other.

What I actually recommend

Stripped of the noise, the evidence-based advice is unglamorous and mostly overlaps with ordinary healthy eating. That is not a disappointment. It means you do not need a special protocol, and you certainly do not need to buy anything.

• Eat a Mediterranean-style base. Vegetables, legumes, whole grains, olive oil, fish, and nuts underpin nearly every positive finding in this field. ^[6]
• Avoid trans fats. The single most consistent dietary risk factor for ovulatory infertility.
• Take folic acid before conceiving. The one supplement with genuinely strong evidence, and it protects the pregnancy as much as the conception.
• Eat enough. Chronic under-eating and low energy availability suppress ovulation.
• Include the male partner. Semen quality responds to diet, and sperm take about three months to develop.
• Don't wait on food to solve everything. Run nutrition changes alongside a medical assessment, not instead of one.
• For the wider hormonal picture, see my article on the hormone balance diet.

So, does diet really affect fertility? Yes, meaningfully, but modestly, and mostly through ovulation, insulin, and sperm quality. It shifts the odds rather than guaranteeing an outcome. Anyone selling you a fertility diet that promises more than that is selling you hope, not evidence.

As a registered dietitian specialising in women's hormonal and metabolic health, I help women build the steady, realistic eating patterns that support ovulation without slipping into restriction. If you'd like a plan built around your body and your diagnosis, book a free consultation, or read more about my PCOS nutrition support.