Food to Avoid During Pregnancy
Kelsey McLaughlin, PhD
Pregnant women commonly wonder if there are certain foods that could impact the health of the baby and pregnancy.
Keep reading to learn which foods pregnant women should avoid and the science behind these recommendations.
Importance of food safety during pregnancy
The growing fetus gets its nutrients from the pregnant mother. The umbilical cord attaches the fetus and the pregnant woman and nutrients in the mother’s blood pass through the placenta into the baby’s blood stream. The blood of the mother and the blood of the developing fetus never come into direct contact.
Therefore, any substances that are in the mother’s blood can be introduced into the baby’s system. Pregnant women are recommended to increase certain nutrients in their diet to support the growth and development of the fetus. On the other hand, pregnant women should also avoid certain foods that could cause harm to the fetus.
Foods recommended during pregnancy
As the baby grows and pregnancy progresses, pregnant women gain weight (discussed in more detail here).
Health Canada encourages pregnant women to following a healthy eating pattern during pregnancy, with high levels of vegetables, fruits, whole grains, low fat milk, fish, lean meats and unsaturated oils.
Despite the common saying that pregnant women are ‘eating for two’, pregnant women need ‘just a little more food’ to meet additional needs of pregnancy. Pregnant women within the normal BMI range only need to add an additional 100 calories to their diet per day, which is approximately the amount of an additional granola bar per day. For the second half of pregnancy, this increases to an additional 300 calories per day.
Let's talk about specific health concerns that doctors have for pregnant women that relate to specific foods.
Risk of Listeria Infection
Listeria is a type of bacteria that can contaminate food, causing food poisoning (also called listeriosis).
Listeria infection can have serious health impacts for pregnant women and the growing fetus, and can be more serious than for the non-pregnant population. It is estimated that pregnant women are at 20x greater risk of listeria infection than the general population. Doctors usually test if a pregnant woman has a listeria infection through a blood test.
Pregnant women who contract listeriosis usually develop a mild flu-like illness, with fever and headache. However, a listeria infection in the pregnant woman can be transferred through the placenta to the developing fetus and the impacts of listeria infection are more severe for the developing fetus, with an overall fetal fatality of 20-30%. The fetus’ immune system may not be fully developed enough to fight off the listeria bacteria.
In addition to fetal loss, listeriosis in pregnant women is also associated increased risk of illness in the newborn, such as meningitis and sepsis in newborns. Of infants born to pregnant mothers infected with listeria, just over 60% completely recovered. If listeriosis is detected in the pregnant women and treated with antibiotics, the impacts of fetal health can be prevented.
High cooking temperatures kill the listeria bacteria in food. Food that is ready-to-eat without further cooking or food that is unprocessed are at risk of listeria contamination.
Pregnant women should avoid:
Unpasteurized foods: unpasteurized dairy products, cheeses and fruit juices / ciders
Pre-packed foods: fruit or vegetables salads, deli meats, prepared meals
Raw or uncooked foods: raw sprouts, meats, poultry, seafood (e.g. sushi), shellfish and eggs
Refrigerated foods that do not require further cooking: pâtés, meat spreads and smoked seafood
Soft cheeses: feta, brie, camembert, blue-veined, Mexican-style cheeses
Health Canada recommends that, in addition to avoiding these food products, pregnant women should minimize their risk of food poisoning through careful cleaning of foods, kitchen equipment and reusable grocery bags, separate foods, cook food to a safe internal temperature and promptly chill food and leftovers to an adequate temperature.
High Mercury Levels
Omega-3 (alpha-linolenic acid) and omega-6 (linoleic acid) fatty acids are referred to as essential fatty acids, meaning that they must be consumed in your diet. Our bodies do not make these fatty acids on their own. The body requires a proper balance of omega-3 and omega-6 levels to support a variety of functions, including complex cell signaling.
Pregnant women are recommended to consume proper amounts of fatty acids in their diets, as omega-3 is critical to support the fetal brain and eye development.
Health Canada encourages pregnant women to consume fish during pregnancy (at least 150 grams of cooked fish per week), as fish are an excellent source of omega-3 fatty acids. Fish are also high in protein, as well as vitamins and minerals, including Vitamin D.
However, it is important to choose fish that are low in mercury and other contaminants. Mercury can build up in fish through exposure to their environment and from the prey they eat – therefore, fish that are larger in size and are predatory have increased mercury levels. When pregnant women consume these types of fish, the organic form of mercury, known as methyl mercury, can cross the placenta and enter the fetus’ blood stream. Methyl mercury can have damaging effects on the fetus’ central nervous system. Scientists have shown that high mercury levels in the pregnant woman’s blood is associated with long-term impacts on the child’s health, including cognitive development.
Health Canada recommends that pregnant women:
Limit the consumption of predatory fish that contain higher levels of methyl mercury to no more than 150 grams per month, including fresh and frozen tuna, shark, swordfish, marlin, orange roughy and escolar
Limit intake of canned (white) albacore tuna to no more than 300 grams per week
High Vitamin A Levels
Health Canada recommends a healthy diet during pregnancy that includes fruits and vegetables with high levels of beneficial vitamins and minerals to support fetal growth and development. Vitamin A is critical to support fetal development, including development of the eyes, bones, teeth, hair and immune system. Vitamin A is found in dark green and orange vegetables and fruits.
As pregnancy progresses, there is an increasing demand for Vitamin A. However, high levels of Vitamin A are associated with birth defects, especially if consumed early in pregnancy. These defects most commonly involve the fetus’ nervous system and cardiovascular system, and is associated with miscarriage.
It is therefore recommended that Canadian pregnant women:
Avoid Vitamin A or fish liver oil supplements
Limit food products high in Vitamin A levels, including liver and liver products
Avoid prenatal supplements that contain more than 10,000 international units of preformed Vitamin A (including acetate, succinate, palmitate)
Can Pregnant Women Eat Sushi?
The answer to this question depends on the type of sushi consumed!
Pregnant women are recommended to avoid raw fish, raw shellfish and smoked seafood, due to concerns regarding listeria infection. In addition, pregnant women should avoid certain types of fish due to mercury levels.
Canadian sources recommend fully cooked and freshly prepared seafood, meat or egg dishes during pregnancy, as well as vegetable-based options.
More generally, pregnant women in Canada are recommended to:
Avoid alcohol consumption
Limit caffeine to moderate intake
Avoid herbal supplements, unless specifically identified as safe for pregnant women
Avoid the artificial sweetener cyclamate, amino acid supplements, soy supplements and limit flaxseed and flaxseed oils
Healthy eating habits that include high levels of vegetables, fruits, whole grains, low-fat milk, fish, lean meats and unsaturated oils are recommended to support a healthy pregnancy. Pregnant women are recommended to avoid food that could increase the risk for listeria infection and have negative impacts on fetal development through high levels of mercury and Vitamin A. Health Canada has additional resources with recommendations for safe food shopping, storage and cooking during pregnancy.
Every woman and every pregnancy is unique. Pregnant women should speak to their healthcare provider to ensure maternal and fetal safety. This article is meant to provide readers with current information and opinions. All medical and treatment decisions should be discussed with your healthcare provider.