4 myths about prenatal nutrition

Prenatal nutrition photoPhoto © AdobeStock

It seems like everyone has advice for a newly pregnant woman about prenatal nutrition — what she should, or should not, be eating. These are perhaps the most common:

“You should be eating for two!”

“You are what you eat!”

“The baby will take what he or she needs, don’t worry!”

“Pregnancy is the only time you get to eat whatever you want – enjoy it!”

But which of these “common wisdom” tidbits about prenatal nutrition should you believe? Here we look at four common pregnancy nutrition myths that should finally be put to rest.

1. “Eating for two” means you should be eating twice as many calories as before you were pregnant.

It’s true that expectant mothers are “eating for two”. But remember, one of those two is very small! According to the National Institutes of Health, most women need only about 300 calories a day more during last six months of pregnancy than they did before they were pregnant. Because 300 calories a day is really not very much food, it is important to make sure those 300 calories are packed with vitamins and other nutrients that the growing baby needs.

Good nutrition choices during pregnancy include:

  • Protein: meat, poultry, fish, eggs, beans and peas, peanut butter, and nuts.
  • Vegetables: fresh, frozen, or canned with no added salt.
  • Fruits: fresh, frozen, or canned without added sugars.
  • Dairy products: milk, cheese and yogurt.
  • Healthful fats: avocados, nuts and seeds, olive oil, canola oil.
  • Whole grains: breads, cereals, pastas, and brown rice.

2. The baby will take any nutrients he or she needs from your body, so it doesn’t really matter what you eat when you are pregnant.

There is a shred of truth in this statement. For example, if the mother’s diet lacks calcium, the baby will leach calcium out of the mother’s bones (which puts the mother at risk of later developing weak bones and osteoporosis). But there are only so many nutrients that a mother’s body can store. During pregnancy, a diet high in empty calories (soda, candy, muffins, cookies, other baked goods, ice cream, desserts, chips, French fries, etc.) will not provide nutrients to the baby or the mother, and both will suffer health problems as a result.

There are several critical types of nutrients that women should make sure to include in their diet during pregnancy:

  • Folate and folic acid — Folate is a B vitamin that helps prevent serious abnormalities of the brain and spinal cord. The added form of folate found in supplements and fortified foods is called folic acid. Having enough folic acid in the diet helps protect the baby’s brain and spinal cord, and lowers the risk of premature birth. Women need 400 to 800 micrograms a day of folate or folic acid before conception and throughout pregnancy. It is important to make sure that there is enough folic acid in the diet before conception, because very important brain and spinal cord development happen within the first few weeks of pregnancy, often before the woman realizes she is pregnant. Good sources of folate and folic acid are fortified cereals, leafy green vegetables, citrus fruits, and dried beans and peas.
  • Calcium – Calcium is a mineral that is needed for strong bones and teeth. It is also needed for the heart, muscles, and nervous system to work normally. Pregnant women need 1,000 milligrams a day, and pregnant teenagers need 1,300 milligrams a day. Good sources of calcium include dairy products, broccoli, kale, and some fortified fruit juices and breakfast cereals.
  • Vitamin D – Sometimes called the “sunshine vitamin”, vitamin D works together with calcium to build bones and teeth. It is also needed for a healthy immune system and normal nerve and muscle function. Pregnant women need 600 international units (IU) a day. There are not many good dietary sources of vitamin D other than fatty fish, like salmon. It is also in fortified milk and orange juice. The body makes vitamin D when skin is exposed to sunlight; however too much sun exposure increases the risk of skin cancer. Some doctors suggest 10-20 minutes of sun exposure on the hands and arms each day without using sunscreen. Other doctors may recommend using a vitamin D supplement. Talk to your doctor about the right approach for you.
  • Iron – Iron is a mineral that is needed for healthy red blood cells that can carry oxygen around the body. Too little iron causes anemia, which can leave the mother feeling tired, weak, and depressed. It also puts the baby at risk of low birthweight and premature birth. Pregnant women need about 27 milligrams daily. Good sources of iron include red meat, poultry, fish, beans, vegetables, and iron-fortified breakfast cereals.
  • Protein – The developing baby needs protein to build strong muscles and to grow normally. Pregnant women need at least 71 grams daily. Good sources of protein include meat, poultry, fish, eggs, beans, nuts, and seeds.

3. It does not matter how much weight you gain when you are pregnant; the baby will be fine.

We have all heard stories of women who were so nauseated during pregnancy that they actually lost weight, and still had healthy babies. Other times we hear of women who gain a lot of weight – 50, 60, or more pounds – and also have healthy babies. It seems like the baby should be fine no matter how little or much weight the mother gains. While there are exceptions to the rule, in general, gaining too little or too much weight in pregnancy can be bad for both mom and baby.

Women who gain too little weight during pregnancy are more likely to have a premature baby (born before 37 weeks of pregnancy) or a baby with low birthweight (less than 5 pounds, 8 ounces). Premature or low birthweight babies are more likely to have breathing problems, bleeding in the brain, heart problems, vision loss, hearing loss, and problems with the intestines. These conditions usually arrive in the first weeks of life. As they grow up, low birthweight babies are at higher risk of diabetes, heart disease, high blood pressure, and obesity. Premature babies are also at risk of behavior problems (attention deficit hyperactivity disorder and anxiety), cerebral palsy, and autism.

Gaining too much weight is concerning as well. Like women who gain too little weight, women who gain too much weight are at risk of having a premature baby. They are also at risk of having a baby that weighs more than 8 pounds, 13 ounces (called fetal macrosomia). This increases the rate of problems during labor and the need for a cesarean birth. In the long term, big babies are at high risk of developing obesity, diabetes, high blood pressure, and heart disease, sometimes as young as age 9 or 10.

According to the National Institutes of Health, weight gain in pregnancy should be gradual, with most of the weight gained in the last trimester. In general, women should gain about 2 to 4 pounds total during the first trimester, and 3 to 4 pounds per month for the second and third trimesters.

Women whose body weight falls into the overweight or obese category before pregnancy should gain less, and women who are underweight before pregnancy begins should gain more.

The following table gives pregnancy weight gain guidelines from the American College of Obstetricians and Gynecologists:

Pre-Pregnancy Weight Category Body Mass Index Healthy Total Weight Gain in Pregnancy
Underweight Less than 18.5 28 to 40 pounds
Normal weight 18.5 to 24.9 25 to 35 pounds
Overweight 25.0 to 29.9 15 to 25 pounds
Obese 30.0 and over 11 to 20 pounds

4. The placenta protects the baby against infection or other harmful substances that might be found in food.

A common misconception is that the baby is completely protected from infection by the placenta. The folk wisdom says that a mother might get sick from bad food, but the baby will be safe. This is simply not true. Many species of bacteria can cross the placenta and affect the developing baby, including E. coli, Listeria, Salmonella, Campylobacter, and Vibrio. Certain substances, like mercury, can easily cross the placenta as well, and can be very toxic to the baby’s growing brain.

To protect the baby, doctors advise that woman stay away from foods that have a higher risk of containing bacteria, parasites, or harmful substances. These include:

  • Unpasteurized milk, and soft cheeses made from unpasteurized milk, such as brie, feta, camembert, roquefort, queso blanco, and queso fresco.
  • Raw eggs or anything with raw eggs, such as cookie dough, brownie/cake batter, homemade eggnog, or homemade mayonnaise.
  • Fish that contain high levels of mercury, such as king mackerel, marlin, orange roughy, shark, swordfish, tilefish, and tuna.
  • Raw or undercooked meat, such as steaks or chops cooked rare, or ground meat with any “pink” left in it.
  • Paté or meat spreads that are refrigerated at the store. Eat canned versions instead, which are safe.
  • Raw fish, such as sushi made with raw fish.
  • Raw shellfish, such as oysters or clams.
  • Smoked seafood that is refrigerated at the store. Eat canned versions instead, which are safe.
  • Unpasteurized juice or cider. It is safe to drink these beverages if they are first heated to a boil for a full minute before drinking.
  • Store-bought salads, such as egg salad, tuna salad, chicken salad, ham salad, pasta salad, and potato salad. Make these salads at home instead with fresh ingredients.
  • Raw or undercooked sprouts, such as alfalfa, clover, mung bean, and radish.
  • Hot dogs, luncheon meats, cold cuts, fermented or dry sausage, and other deli-style meat and poultry. These can be eaten, but must be reheated until they are steaming in order to kill possible bacteria.

Further reading

American College of Obstetricians and Gynecologists. Weight gain during pregnancy.

Foodsafety.gov. Checklist of foods to avoid during pregnancy.

March of Dimes. Low birthweight.

March of Dimes. Long-term health effects of premature birth.

Mayo Clinic. Pregnancy diet: focus on these essential nutrients.

U.S. National Library of Medicine. Medline Plus. Pregnancy and nutrition.

About the Author

Jillian Lokere
Jillian is a science/medical writer who specializes in communicating complex scientific and medical ideas in a meaningful and engaging way. She holds a master's degree in biomedical science from Harvard University and a bachelor's degree in biological science from Stanford University. In addition, Jillian conducted two years of doctoral-level research in the Department of Genetics as part of Harvard's Biological and Biomedical Sciences program. She has more than 13 years of experience in writing about the life sciences and medicine.