Two different lists get merged constantly. One is 'foods that may affect your ability to conceive'. The other is 'foods that carry an infection or toxicity risk once you are pregnant'. They overlap, but they are not the same thing, and treating them as one produces a diet that is needlessly restrictive in some places and not careful enough in others.
- Trans fats have the clearest dietary association with ovulatory infertility — largely gone from supermarket food, still present in some fried and imported baked goods.
- Alcohol is the item with the strongest case for cutting: heavy intake reduces fertility, and no safe level is established in early pregnancy.
- Caffeine under about 200 mg a day is generally considered fine; the concern starts at consistently high intakes.
- High-mercury fish matters because mercury accumulates over months, so the time to stop is before conception, not after.
- Soy, dairy and gluten are the three most commonly avoided foods with the least supporting evidence.
Worth avoiding, with reasons
Ranked by the strength of the evidence behind the advice.
Alcohol
Heavy drinking measurably reduces fertility in both partners and raises miscarriage risk. Lower intakes are less clear-cut, but because you can be several weeks pregnant before knowing, and no safe level has been established for the developing embryo, cutting it out while trying is the position virtually every health body takes.
Trans fats
The Nurses' Health Study found a striking association between trans fat intake and ovulatory infertility — replacing a small fraction of energy from trans fats with unsaturated fat was linked to substantially lower risk. Look for 'partially hydrogenated' on labels, mostly in commercially fried food, some imported baked goods and cheap margarines.
High-mercury fish
Shark, swordfish, marlin, king mackerel, tilefish and bigeye tuna accumulate methylmercury, which is neurotoxic to a developing brain and clears from the body over months. That slow clearance is exactly why this belongs on a pre-conception list rather than a pregnancy one.
Very high caffeine
Under about 200 mg daily is widely considered acceptable. Consistently high intakes — above roughly 300 to 500 mg — have been associated with longer time to pregnancy and higher miscarriage risk in several cohorts, though confounding by nausea and by smoking complicates the picture.
Ultra-processed, high-glycaemic patterns
A dietary pattern heavy in refined carbohydrate and sugar-sweetened drinks is associated with insulin resistance, which matters a great deal in PCOS. This is about the overall pattern rather than any single food.
High-dose vitamin A (retinol)
Liver, liver pâté and retinol supplements can deliver enough preformed vitamin A to be teratogenic. Beta-carotene from vegetables is not a concern — the body regulates its conversion.
Where 200 mg of caffeine actually lands
Most people underestimate their intake by roughly one drink, mainly because of coffee-shop serving sizes.
| Drink | Typical caffeine | Notes |
|---|---|---|
| Instant coffee, 1 mug | ~100 mg | Two mugs reaches the ceiling |
| Filter coffee, 1 mug | ~140 mg | One and a half mugs reaches it |
| Coffee-shop large latte | ~150–200 mg | Often a whole day's allowance in one cup |
| Espresso, single shot | ~60–80 mg | Double shots are the hidden multiplier |
| Tea, 1 mug | ~75 mg | Green tea somewhat less |
| Cola, 330 ml | ~40 mg | Adds up quickly across a day |
| Energy drink, 250 ml | ~80 mg | Check the can; some are far higher |
| Dark chocolate, 50 g | ~25 mg | Minor unless you eat a lot |
Cutting soy, dairy and gluten while still drinking four coffees and a glass of wine is optimising the wrong end of the list.
Commonly avoided, poorly supported
Cutting these out has a real cost — less variety, more stress, and a diet that is harder to sustain — for very little demonstrated benefit.
Soy
The phytoestrogen worry comes from animal studies at doses far beyond normal human intake. Human data is mixed, and some studies find neutral or even favourable associations with fertility outcomes. Normal dietary amounts are not a demonstrated problem.
Dairy
Often cut out entirely on the assumption that hormones in milk are harmful. The observational data does not support avoidance, and one large cohort actually associated full-fat dairy with lower ovulatory infertility risk. Unpasteurised dairy is the real concern, and only for infection risk.
Gluten
Undiagnosed coeliac disease is genuinely associated with subfertility and recurrent loss — which is an argument for getting tested, not for cutting gluten out blind. Removing it before testing makes the diagnosis harder.
All fish
Some people avoid fish entirely after hearing about mercury. Oily fish is one of the best sources of omega-3 and vitamin D and is actively recommended — two portions a week of low-mercury varieties like salmon, sardines and trout.
The separate list: once you might be pregnant
These are infection and toxicity risks to the pregnancy rather than fertility issues. They become relevant from the moment conception is possible — which, if you are trying, is every cycle:
- Unpasteurised milk and soft mould-ripened cheeses such as brie and camembert, plus soft blue cheeses — listeria risk.
- Pâté of all kinds, including vegetable pâté — listeria, plus high vitamin A in liver-based versions.
- Raw or undercooked meat and cured meats such as prosciutto and salami — toxoplasmosis risk.
- Raw or lightly cooked eggs, unless they carry a recognised food-safety mark such as the British Lion stamp.
- Raw shellfish, and smoked fish that has not been thoroughly cooked.
- Liver and liver products, because of preformed vitamin A.
- Any unwashed salad or vegetables carrying soil residue.
The pattern matters more than the list
Build the pattern, then stop reading lists
Study after study lands on the same eating pattern rather than on individual villains: plenty of vegetables and fruit, whole grains instead of refined ones, legumes, fish, olive oil, nuts, and less processed meat and sugar. It is the Mediterranean pattern under various names, and it consistently associates with better fertility outcomes and better pregnancy outcomes.
That is a more useful frame than a list of prohibitions. A diet built on avoidance gets more restrictive each time someone mentions a new suspect food, and it eventually becomes another source of stress in a process that already has enough. Cut the four items that have evidence behind them, build the pattern, and stop there.
When to ask for help
Worth raising with a clinician or dietitian:
- A history of digestive symptoms, unexplained anaemia or unexplained infertility — ask about coeliac testing before removing gluten.
- Following a vegan diet while trying to conceive, which needs planned B12, iron, iodine and omega-3.
- Any eating pattern that has caused periods to become light, irregular or absent.
- A BMI under 19 or over 30 alongside cycle irregularity.
If something feels wrong and it is not on this list, that is still a reason to call. Lists like this are a floor, not a ceiling.
Questions about diet
Can I drink alcohol while trying to conceive?
The safest answer is no, from the point in each cycle where conception is possible. Heavy drinking clearly reduces fertility; lower intakes are less certain. The reason most guidance says to stop entirely is that you can be several weeks pregnant before you know it, and no safe level has been established for the embryo.
How much coffee is safe when trying to get pregnant?
Up to about 200 mg of caffeine a day — roughly two mugs of instant coffee, or one large coffee-shop drink — is the commonly used ceiling, and it is the same limit advised in pregnancy. Remember tea, cola, energy drinks and chocolate count toward it.
Does soy really lower fertility?
Normal dietary amounts have not been shown to. The concern originates in animal studies using doses far above human intake. Human data is mixed and includes neutral and favourable findings.
Should I stop eating fish because of mercury?
No — swap types rather than stopping. Avoid shark, swordfish, marlin, king mackerel and bigeye tuna. Keep eating salmon, sardines, trout and mackerel, which are recommended at about two portions a week for omega-3 and vitamin D.
Does a low-carb diet help fertility?
It can help if you have PCOS with insulin resistance, where reducing refined carbohydrate improves ovulation. For someone ovulating normally there is no evidence that carbohydrate restriction improves conception rates, and very low intakes can disrupt cycles.
Sources
Guidance bodies and peer-reviewed literature used while writing this guide.
- Foods to avoid in pregnancy — NHS
- Dietary fatty acid intakes and the risk of ovulatory infertility — American Journal of Clinical Nutrition
- Diet and fertility: a review — American Journal of Obstetrics and Gynecology
This guide is general information, not medical advice, and it cannot account for your history. See our medical disclaimer and editorial policy.
