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Truths and myths about nutrition during pregnancy

Truths and myths about nutrition during pregnancy

12 min read

There's no shortage of opinions about what you should and should not eat and drink while pregnant. If you’re confused by all the seemingly conflicting advice, you’re not alone. Nutrition is a relatively young science and our understanding of the role nutrients play in human physiology is rapidly evolving — hence the whole butter is bad, then butter is back confusion.

What we can agree on across the board is that nutrition during pregnancy matters. It matters for your health, from keeping your energy levels up to helping to prevent or manage gestational diabetes (which, in turn, reduces your lifelong risk for developing type 2 diabetes). What you eat matters equally for the healthy development of the baby-to-be — and for the health of that baby all the way into adulthood:

  • The birthing person's environmental exposures and nutrition status are believed to influence genetic expression in the fetus, which seems to play a role in determining adulthood risk for chronic conditions.
  • This fetal programming may even extend intergenerationally, meaning lifestyle choices while pregnant can influence the genetic expression, and thus the health, of future grandchildren. (Guess we need to replace the adage "you are what you eat" with "you are what your grandmother ate.")

With that powerful motivator in mind, let’s dive into what we can reasonably conclude from the existing research to clear up some of the confusion around myths like the concept of "eating for two" and complete abstinence from coffee, fish, and soft cheeses.

But first: Why is pregnancy nutrition so confusing?

Pregnancy nutrition is particularly prone to conflicting recs because we don’t have as many randomized controlled trials (RCTs), the gold-standard methodology for research that allows scientists to make cause-and-effect statements (like "smoking causes cancer"). These RCTs start with study participants who are as similar as possible in all demographic and lifestyle characteristics, and then randomly separated into an intervention group that receives a treatment (e.g., eats the food), and a control group that does not receive the treatment (e.g., does not eat the food).

In pregnancy, RCTs often become ethically questionable — it’s not exactly ethical to ask one group of pregnant people to binge drink so that the researchers can compare the health effects to a control group abstaining from alcohol. Thus, for almost every controversial topic in prenatal nutrition, from raw cheese and deli meats to caffeine and alcohol, we often don’t have the caliber of research needed for more definitive, universal recommendations.

We do, however, have enough observational research to make reasonably well-supported recommendations. Researchers can ask people to report on what they ate and drank while pregnant and glean a reasonable understanding of what it takes to grow a healthy baby. This observational research is what we'll use below to examine some of the more common pregnancy-nutrition myths — and highlighting what's ultimately the most important to pay attention to, nutritionally-speaking.

MYTH: You’re "eating for two."

Truth: It's important to focus instead on nourishing for two.  

In general, the American College of Obstetricians and Gynecologists (ACOG) and the Centers for Disease Control (CDC) recommend no additional calories during the first trimester, then an additional 300-400 calories per day during your second and third trimesters — but everyone's different. (For reference, 300-400 calories could mean a large apple with two tablespoons of peanut butter, two slices of whole grain toast with half of a medium avocado, or a cup of plain, nonfat Greek yogurt with half of a cup of granola.)

Talk to your healthcare provider about the exact amount of calories that's recommended for you, which will vary based on your starting weight, physical activity levels, how many fetuses you’re carrying, and other factors. OB-GYN and Modern Fertility medical advisor Dr. Eva Luo, MD, MBA explains that for some people, the expectation may be no weight gain at all — or even weight loss. But, again, everyone's different.

While the recommendation isn't to double the amount you eat, you do need significantly more nutrients for a healthy pregnancy (like iron and choline, for example).* Focus on nutrient-rich foods from all of the food groups: Build each meal around fruits, vegetables, whole grains, nuts, seeds, healthy fats, and lean meat and proteins (and don't forget the importance of a prenatal vitamin!).

MYTH: Any amount of coffee is unsafe.

Truth: 1-2 cups of coffee per day is considered safe.

This is one of the most controversial topics, as you’ll hear recommendations across the spectrum from no amount of caffeine is safe to it's okay to drink upwards of three cups of coffee per day. The reality is that we know that caffeine crosses the placenta, but from there, the effects are not fully understood. The primary concern cited about caffeine is the risk of miscarriage, which is likely only a concern for those consuming more than 300 mg of caffeine each day (that’s more than three cups of strong coffee).

There are two major factors in the controversy around caffeine recommendations during pregnancy:

  • The available research has significant limitations: As discussed above, a lack of randomized controlled trials leaves us relying largely on people’s ability to remember how much caffeine they consumed and to report it accurately. This methodology is flawed not only because of poor memory, but also because of societal pressure bias, in which people who believe a behavior is bad, like drinking coffee, will underreport their usage.
  • The research on caffeine is also complicated by the nausea issue: Nausea in the first trimester (aka morning sickness) is, for reasons not well understood, associated with decreased risk of miscarriage. The catch with nausea is that it can also make you averse to coffee. People who have had previous births report the first telltale of a recurrent pregnancy, before noticing a missed period, is the return of their aversion to coffee. This makes the data reporting an association between coffee consumption and higher risk of miscarriage difficult to interpret — if people felt well enough to drink two or more cups of coffee, how do we know if it was the lack of nausea (also referred to as weak placenta signaling) or the coffee itself that caused the miscarriage?

Digging through the literature with these caveats in mind, here's what researchers have found:

  • Some prospective studies, meaning research that asks people to track their intake as they go rather than relying on memory, report no association between caffeine and miscarriage risk (see here and here).
  • Others report that the risk of miscarriage only jumps up after exceeding 300 mg of caffeine per day.

Building on the second bullet from above, just as many (if not more) studies have shown a dose-response risk, indicating that the more caffeine you consume in early pregnancy, the higher the risk of miscarriage:

  • One systematic review reported a 7% increase in miscarriage risk for each 100 mg increase in daily caffeine consumption.
  • A systematic review in 2017 suggested that miscarriage was 37% more likely among pregnant women who consumed 300 mg caffeine per day, while pregnant people drinking 600 mg per day caffeine had an almost 2.5 times increased risk for miscarriage.
  • One finding that is consistent is that 200 mg per day of caffeine or less poses very little risk of miscarriage. ACOG states that less than 200 mg per day of caffeine “does not appear to” cause miscarriages or preterm birth. This means you can safely enjoy 1-2 cups (depending on how strong you take it) of coffee per day.

For reference, here are the approximate amounts of caffeine in different beverages, as  reported by Mayo Clinic and the Journal of American Dietetic Association (though these numbers vary significantly based on how strongly the coffee or tea is brewed):

  • 8 oz of coffee: 96-150 mg (though a Starbucks 8 oz brewed coffee has closer to 160 mg of caffeine)
  • An espresso shot: 64 mg
  • A 16 oz latte: 100 mg
  • 8 oz of black tea: 28-60 mg
  • 8 oz of green tea: 20-30 mg
  • ½ a teaspoon of matcha: 35 mg
  • 8 oz of decaf coffee: 2 mg

If you love your morning coffee or tea, you don’t have to cut it out completely in the name of pregnancy. Just replace that second or third cup with something less caffeinated, like green tea, matcha, or a decaf latte.

MYTH: Fish is not safe in pregnancy.

Truth: It’s safe to eat 2-3 servings of low-mercury fish each week.

When it comes to fish, there are two main concerns: the risk of food poisoning from raw fish and the risk of heavy metal toxicity (specifically from methyl mercury). These concerns, however, do not justify cutting out fish entirely. Fish are good sources of lean protein, and depending on the variety, they can also be rich sources of many nutrients that are especially essential during pregnancy but challenging to get from other foods. These nutrients include vitamin D, omega-3 fatty acids, and calcium. In my professional opinion, the benefits of eating fish outweigh the risks — if you can make informed choices about which fish to eat.

Potential risk 1: Food poisoning

Raw fish (think sushi or sashimi) can carry two potentially harmful bacteria: salmonella and campylobacter. Although salmonella and campylobacter can make you seriously sick, the risk of contracting these foodborne illnesses is no greater during pregnancy than during other times in your life. If you were to get food poisoning while pregnant, it wouldn't be fun (and you'd want to take extra care not to get too dehydrated ) — but the bacteria itself poses minimal risk to the fetus.

If you choose to take the minimal risk by eating raw fish, follow common-sense food-safety precautions (i.e., opt for the sushi at a well-reviewed restaurant rather than the gas station).  Raw or cooked, avoid fish that has been sitting out at room temp for more than four hours.

Two other notes of caution:

  1. Raw shellfish, like oysters and clams, carry an additional risk of toxoplasmosis — an illness transmitted by a parasite that can have serious impacts on the fetus. While pregnant, cooking your oysters and clams is the safer route.
  2. Traditional lox is cold-smoked, a process that cures the fish in temperatures too low to kill the harmful bacteria. The result is an additional risk of listeria poisoning, which can be very dangerous to you and the growing baby-to-be. If you get smoked or cured salmon, make sure the label reads "high heat" or "hot smoked" to avoid this risk.

Potential risk 2: Mercury toxicity

Mercury is a heavy metal that can accumulate in our bodies and, in cases of over-exposure, can cause neurological damage. Researchers have found that higher mercury levels in the expecting parent may result in slightly lower IQ scores in their children.

Rather than taking this information and cutting out fish altogether, keep in mind that not all varieties of fish have high levels of mercury.If you want to eat fish, you can avoid the high-mercury varieties (see the Natural Resources Defense Council’s table). Here are some general rules of thumb:

  • Avoid larger fish that are higher up on the food chain: These larger swimmers accumulate more mercury as they eat smaller fish, and include less-common options like shark or tilefish, as well as more common ones like swordfish, grouper, albacore, or ahi tuna.
  • Opt for smaller fish instead: Smaller fish, like sardines, anchovies, herring, and king mackerel are very low in mercury. You can also find brands of canned tuna, such as Safe Catch and Wild Planet, that specify sustainable fishing practices and "low-mercury" content in the tuna.

Having assessed these benefits and risks, ACOG, the Environmental Protection Agency and the Federal Drug Administration all recommend that pregnant people eat 2-3 servings of low-mercury fish each week, limiting tuna to one serving per week, and avoiding high-mercury varieties.

Another consideration when thinking about whether or not to eat fish while pregnant is that many fish have brain-building DHA (an essential omega-3 fatty acid), which may counteract any risk of harm from heavy metal exposure. If you prefer to avoid fish, you can also get DHA from algae-based supplements (like the Modern Fertility Prenatal Multivitamin).

One type of fish has a health halo because it's low in mercury and rich in DHA: salmon!

MYTH: Soft cheese isn't safe either.

Truth: Avoid raw cheese — soft cheese is fine if it’s pasteurized.

The concern with soft cheeses is listeria poisoning. Although relatively rare, affecting about 1 in 8,000 pregnancies each year, listeria can be very dangerous for you and a developing fetus. But, as cheese ages, this can stave off the risk of listeria (hence the myth to only eat hard cheese and to avoid soft cheese). However, aging is not sufficient to eliminate the listeria risk if raw milk is used. Your ticket to safety is understanding that listeria is killed by pasteurization, a process that heats foods to a temperature lethal to bacteria. Pasteurization is the safest bet, whether the cheese is soft or hard.

You also may have heard warnings about European cheeses, but the origin of the cheese doesn’t matter — whether they come from France or Wisconsin, the important distinction is the pasteurization of those dairy products.

"Are you guaranteed to get listeria if you accidentally eat some pasteurized cheese? No — but your risk is higher," explains Dr. Luo. (This is also why washing fruits and veggies is so important.)

Now that we've covered the myths, what's most important to know about pregnancy nutrition?

Let's start with the guidelines from the leading body of OB-GYNs. ACOG recommends making sure you're getting the following nutrients during pregnancy:

  • Folate (aka folic acid or methylfolate) to support fetal neural tube (brain and spinal cord) development*
  • Iron to form red blood cells and hemoglobin — the protein in your blood that transports oxygen from your lungs throughout the body*
  • Choline to support fetal neurodevelopment*
  • Omega-3 fatty acids (DHA and EPA) to help develop the fetal brain and retina*
  • Vitamin C to promote the growth of all connective tissue (skin, joints, etc.) and a healthy immune system*
  • Vitamin A to support fetal eye development and good vision, as well as a healthy immune system*
  • Vitamin B-6 to boost your energy while you're pregnant*
  • Vitamin B-12 to help keep the central nervous system on track*
  • Iodine to help with developing a healthy fetal brain and maintaining thyroid health*
  • Calcium to help with strong bones and teeths
  • Vitamin D3 to promote bone health and improve immune function for you and the fetus*

If you’re vegetarian or vegan, the list of nutrients to pay attention to grows longer: Vegetarians often aren't getting enough iron, zinc, omega-3 fatty acids, vitamin D, choline, and B vitamins from food alone — and vegans are sometimes deficient in calcium as well. (Read up on other key nutritional considerations when you're vegetarian or vegan here.)

How can you increase your body's reserves of these key nutrients? Through balanced eating and taking a prenatal supplement. When I say "balanced eating," I mean healthy eating from a variety of food groups — not a so-called "pregnancy diet." In practice, this looks like eating:

  • Tons of fresh fruits and vegetables (8-10 servings a day)
  • Whole grains (like brown rice or bread) over white when possible
  • A good amount of plant-based quality protein (e.g., lentils, beans, quinoa, seeds, legumes, or soy)
  • Low-mercury, cold-water fatty fish for the vitamin D and for the omega-3s (if you eat fish)
  • Nutrient-dense eggs (including the yolk!)

Dr. Luo's advice for getting enough healthy foods during pregnancy? "I suggest eating a colorful plate of food. Not all brown/yellow. We want to see some green and all of the vibrant colors of fruits out there!"

While I'm all about taking a food-first approach, many nutrients essential for a healthy pregnancy aren't readily available from food alone (like vitamin D, choline, and DHA). That's where prenatal vitamins come in: If a prenatal has a good assortment of the nutrients recommended for pregnancy, including 400 micrograms (mcg) of folate, it can help you bridge the gap between low intake from food and higher nutrient demands.

The Modern Fertility Prenatal Multivitamin

​​The Modern Fertility Prenatal Multivitamin is designed to support your body before, during, and after pregnancy (whether or not you're chestfeeding/breastfeeding). It includes all of ACOG's recommended nutrients except for calcium — which many prenatals don't include because it can block the absorption of iron and supplementation maxes out at ~500 mg. Both of these factors can make it difficult to put calcium alongside other nutrients in a prenatal. Instead, the Prenatal Multi has a calcium booster: vitamin D.*

On top of 10 ACOG-recommended nutrients, the Prenatal Multi also has zinc (which can be up to 50% deficient in vegetarians) and biotin (which a third of pregnant people are deficient in).

The bottom line: Pregnancy nutrition doesn't have to be complicated

What you eat during pregnancy doesn't have to be radically different from any other adult's version of balanced eating. What's most important is following food-safety precautions, keeping caffeine to 1-2 cups per day, eating low-mercury fish twice per week (or taking a DHA supplement), choosing pasteurized cheese over unpasteurized, and eating a variety of nutritious foods. "For those that really want to dive into the literature," adds Dr. Luo, "I actually recommend Emily Oster's Expecting Better. She provides a very easy-to-read review of the available literature."

Whether you're currently pregnant, trying to get pregnant, or a few years out from thinking about kids, the free online Modern Community is here for you with real-talk support for wherever you're at — and your online space for unfiltered convos about all things women's health. Join today to connect with other people with ovaries who are on the same wavelength you are.

*This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This article was medically reviewed by Dr. Eva Marie Luo, MD, MBA, OB-GYN at Beth Israel Deaconess Medical Center and Clinical Lead for Value at the Center for Healthcare Delivery Science at Beth Israel Deaconess Medical Center.

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Anna Bohnengel, MS, RD, LD

Anna, MS, RD, LD is co-founder of Alavita Nutrition. With clinical training from the NIH, she teaches women how to nourish themselves so they can take control of their health. alavitanutrition.com

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