Pregnancy diet: what to eat and which foods to avoid

How much weight should you gain during pregnancy?

It depends on your body mass index (BMI) before pregnancy, the relationship between your weight and height. The Sociedad Española de Ginecología y Obstetricia (SEGO) specifies ranges for a pregnancy with one baby [1]. See “Listeria in pregnancy”.

If you started at a healthy weight, the expected gain is 11.5 to 16 kg; with obesity, 5 to 9 kg [1]. If you are overweight, the range is 7 to 11.5 kg [2], and if you are underweight, 12.5 to 18 kg [2].

Weight gain is usually small in the first trimester, around 0.5 to 2 kg [2], and increases in the second and third. A healthy pregnant woman should not restrict energy intake to limit body fat, unless she has obesity or gains too much weight [1]. In that case, her care team will advise her.

Monitoring weight helps prevent complications such as gestational diabetes and pre-eclampsia. If you want to lose weight, do so before trying to conceive or after giving birth. You can find our weight-loss diet for that time.

What to eat in the first trimester if you feel nauseous

During the first twelve weeks, you need very little extra energy compared with before, but the quality of what you eat matters. Nausea, dizziness and aversions to certain smells are common. They are linked to hormonal changes and slower stomach emptying.

Spread your food across five or six small meals and choose mild foods. Have something dry before getting up, such as a rusk or toast, as this can ease early-morning dizziness. It is usually better to drink between meals than during them. Choose steaming, baking or boiling rather than frying or rich stews.

If your appetite is low, cold or warm dishes may be easier to tolerate than very hot or strongly scented foods. If you vomit so much that you cannot keep fluids down, do not wait; see the section on when to seek medical care.

How to meet your needs in the second and third trimesters

From week 13 onwards, your baby’s and placenta’s growth increases your needs. In the second and third trimesters, add 340 to 450 kcal a day to what you were eating [1]. You can do this without doubling portions: a handful of nuts, fruit with yoghurt, or a slightly larger serving of pulses or whole grains is enough.

Two discomforts are common at this stage. For constipation, the Organización Mundial de la Salud (OMS) recommends starting with dietary changes [3]. This means drinking more water, eating more fibre from vegetables, pulses, fruit and whole grains, and walking every day.

Heartburn can worsen because the uterus pushes the stomach upwards. Have dinner two or three hours before going to bed and avoid lying down just after eating. Cut back on foods that bother you; coffee, chocolate, citrus fruit and spicy foods are common triggers.

Which supplements are needed during pregnancy?

There are three nutrients to keep in mind. Folic acid is recommended from at least one month before pregnancy and throughout the first three months [1]. Your midwife or gynaecologist advises you on folic acid; your dietitian-nutritionist helps with the eating plan that accompanies it. It prevents neural tube defects, such as spina bifida. If you have previously had a pregnancy affected by one of these defects, your doctor will adjust the advice.

For iodine, use iodised salt and include dairy products and fish. During pregnancy and breastfeeding, your midwife or doctor will assess whether you need an iodine supplement [1].

The OMS recommends an iron supplement for all pregnant women [3]. In Spain, it is tailored to each person based on blood test results [1]. Check the supplement with your doctor or dietitian-nutritionist; do not start or stop it on your own.

Iron from food is better absorbed when you combine pulses, eggs or meat with foods rich in vitamin C, such as peppers or fresh fruit.

Which foods should you avoid during pregnancy?

Food-borne infections are uncommon, but some can affect the baby. The Agencia Española de Seguridad Alimentaria y Nutrición (AESAN) provides guidance on three risks: listeriosis, toxoplasmosis and mercury [4].

To reduce the risk of listeriosis, avoid raw milk and soft, fresh or blue cheeses unless the label says they are made with pasteurised milk [4]. The same applies to refrigerated pâtés and refrigerated smoked fish [4].

Take precautions against toxoplasmosis if you are not certain that you are immune. Do not assume that you have had the blood test. Avoid raw cured meats, such as cured ham, chorizo, salchichón or salami [4]. You can eat them cooked to 70 °C at the centre, for example in croquettes, pizzas or stews [4].

For fish, avoid four large species that accumulate mercury: swordfish, shark (including dogfish, mako and blue shark), bluefin tuna and pike [5]. For other fish, at least three portions a week are recommended, prioritising oily fish, which is rich in omega-3 [5]. Sardines, anchovies, mackerel, horse mackerel and salmon are good choices, as are hake and sole. If you need a DHA supplement during pregnancy or breastfeeding, your care team will assess this and your doctor or dietitian-nutritionist will advise you. Ask for advice before taking omega-3 supplements if you use anticoagulants or antiplatelet medicines.

Also avoid seaweed. Pregnant and breastfeeding women are advised not to eat it because of its high iodine content, particularly kombu [6]. There is no safe amount of alcohol for health (OMS): the less, the better. Avoid it completely during pregnancy, breastfeeding and childhood. Do not drink if you are going to drive or if your medication does not allow it.

Common mistakes we see in consultations

There are four things we hear in consultations almost every week. None is serious on its own, and all are easy to address.

Eating for two. You need very little extra energy in the first trimester, and after that one extra snack a day is enough. Eating twice as much can lead to weight gain that is then difficult to lose.

Dieting to avoid gaining weight. A weight-loss diet during pregnancy can deprive your baby of the energy and micronutrients they need. Your midwife monitors your weight at each appointment.

Avoiding all cheese and all fish out of fear. Cheeses made with pasteurised milk and most fish are safe, and provide calcium, iodine and omega-3. The list of foods to avoid is short and specific.

Assuming that natural means harmless. Many women take herbal teas for nausea or digestion without mentioning them. Do not take multivitamins or herbal preparations without checking first. Before taking a plant-based product with an active ingredient, ask your pharmacist or doctor, especially if you take medication or are pregnant.

Can you follow a vegetarian or vegan diet during pregnancy?

Yes. The US Academy of Nutrition and Dietetics considers a well-planned vegetarian or vegan diet suitable during pregnancy [7]. Vitamin B12 supplementation is essential on a vegan diet [7]. Check your vitamin B12 supplement with your doctor or dietitian-nutritionist. Plant foods do not provide it reliably, and a deficiency affects the baby’s neurological development [7].

You also need to keep an eye on protein, iron, zinc, iodine, calcium, vitamin D and omega-3 [7]. Planning your diet with a dietitian-nutritionist can help you combine pulses, grains, seeds, nuts and fortified foods without unnecessary supplements or deficiencies.