Most prenatal nutrition conversation focuses on supplements — folic acid, iron, DHA (all covered in our separate articles). But supplements exist to fill gaps in an otherwise adequate diet. The evidence on whole-diet patterns during pregnancy is equally important and, for most women, has a larger impact on pregnancy outcomes than any single supplement.
Dietary patterns: the Mediterranean diet evidence
The strongest evidence for a specific dietary pattern during pregnancy comes from research on the Mediterranean diet — characterised by high intake of fruits, vegetables, whole grains, legumes, nuts, olive oil, and fish, with moderate dairy and limited processed foods and added sugars.
A 2017 RCT by Assaf-Balut and colleagues found that a Mediterranean diet supplemented with extra virgin olive oil and pistachios reduced the incidence of gestational diabetes by 35% compared to standard dietary advice.1 Subsequent observational studies have associated Mediterranean-style eating during pregnancy with reduced risk of pre-eclampsia, small-for-gestational-age birth, and preterm birth, though the evidence from RCTs on these outcomes is still developing.2
The US Dietary Guidelines for Americans 2020–2025 recommend a balanced eating pattern during pregnancy that aligns closely with Mediterranean principles: emphasis on whole grains, varied protein sources (including seafood 2–3 times per week), fruits, vegetables, and healthy fats, with limited added sugars, saturated fat, and sodium.2
Calorie needs: smaller than you think
Pregnancy increases calorie requirements — but not by as much as the cultural narrative suggests. ACOG guidance: no additional calories are needed in the first trimester. An additional 340 calories per day are recommended in the second trimester, and approximately 450 calories per day in the third trimester.3 For context, 340 calories is roughly a small sandwich or a bowl of yoghurt with fruit and nuts — not a second meal.
Caffeine
Current guidelines from ACOG and NICE recommend limiting caffeine intake to 200 mg per day during pregnancy — approximately one 350ml cup of filter coffee or two cups of tea.3 4 The evidence linking moderate caffeine intake (under 200 mg) to adverse pregnancy outcomes is inconsistent, but higher intakes have been associated in observational studies with increased risk of miscarriage, low birthweight, and small-for-gestational-age birth. A 2020 review by James (BMJ Evidence-Based Medicine) argued that no safe level of caffeine consumption during pregnancy could be established, though this conclusion has been contested and current guidelines maintain the 200 mg threshold.5
Food safety
The food safety restrictions during pregnancy are based on specific infection risks, not general caution. The key pathogens and the foods that carry them:
Listeria monocytogenes: Can cause listeriosis, which is associated with miscarriage, stillbirth, and neonatal infection. Avoid unpasteurised milk and soft cheeses made from it, pre-prepared salads and sandwiches from delicatessen counters, smoked fish (unless cooked), and pâté. The risk is from ready-to-eat foods that are stored at refrigeration temperature for extended periods.6
Toxoplasma gondii: Can cause congenital toxoplasmosis. Avoid raw or undercooked meat, unwashed fruits and vegetables, and contact with cat litter (or wear gloves if unavoidable). Cooking meat to a safe internal temperature (at least 70°C throughout) kills the parasite.6
Salmonella: Avoid raw or undercooked eggs (unless they carry the Lion mark in the UK, indicating vaccination of the flock) and raw or undercooked poultry.6
Mercury in fish: Avoid high-mercury fish (shark, swordfish, king mackerel, tilefish, marlin). Limit tuna to no more than 2 steaks or 4 medium cans per week. Low-mercury fish (salmon, sardines, anchovies, trout) are actively encouraged — 2–3 servings per week for omega-3 and protein.2
Weight gain
ACOG recommends weight gain targets based on pre-pregnancy BMI: 12.5–18 kg for underweight women (BMI below 18.5), 11.5–16 kg for normal weight (BMI 18.5–24.9), 7–11.5 kg for overweight (BMI 25–29.9), and 5–9 kg for obesity (BMI 30 or above).3 These are guidelines, not mandates — individual variation exists, and weight monitoring should be discussed with your provider in the context of your overall health, not treated as a pass/fail metric.
What this means in practice
Nutrition during pregnancy is a pattern, not a performance. The evidence supports eating a varied, whole-food-focused diet with adequate protein, healthy fats, and micronutrient-dense foods. It supports limiting caffeine and avoiding specific high-risk foods. It does not support restrictive eating, diet culture anxiety, or the idea that a single food choice will determine your baby's health.
If your diet is broadly aligned with Mediterranean or whole-food principles, you are covering the major evidence-based bases. Supplements fill specific gaps — they do not replace the foundation.
