Shellfish: Why these nutrient-dense foods are beneficial during pregnancy

Recently, I posted an in-depth review of the benefits of consuming organ meats like liver to not only support prenatal health and fetal development but also to encourage nose-to-tail eating as a means of sustainable food consumption. 

Today, I want to shift the focus to a different kind of food that’s also nutrient-dense and sustainable, but can add some variety and may please a more fish-loving palate: shellfish!

Shellfish: Why these nutrient-dense foods are beneficial during pregnancy

You have probably heard a lot of “real food” nutritionists or practitioners talk about the benefits of eating seafood for inflammation reduction, brain health, and fetal development. Salmon is a beloved seafood that is touted for its health benefits, and it certainly has many. But I want to explore seafood beyond salmon and share a few nutrient-powerhouses you may not have expected. 

I’ll review what shellfish are, their nutritional composition and how that’s relevant to pregnancy, considerations regarding heavy metals and food safety, and provide some tips for incorporating them into your diet. 

First, let’s start with some definitions. 

What are shellfish?

Shellfish are somewhat aptly named – they are aquatic animals that have exoskeletons or “shells” and are the blanket term for a wide variety of seafood. Commonly known shellfish are creatures like shrimp, lobsters, and clams. While they are not technically fish (they are low on the food chain and eat a diet primarily of plankton), shellfish do contain many nutrients that we commonly associate with fish and marine life that are beneficial to pregnancy. 

There are two subclasses of shellfish: crustaceans and mollusks. Crustaceans typically have a hard shell and joints (i.e lobsters and crabs), whereas mollusks can either have a symmetrical body with a protruding head (i.e. octopuses and squids) or hard, hinged shells (i.e. clams and oysters). The hinged-shell organisms belong to a class of mollusks called bivalves.  

Bivalve shellfish are incredibly nutrient-dense in vitamins and minerals needed during pregnancy

If you’ve followed my work for a while, you know I’m a proponent of eating animal products, as they are chock-full of the micronutrients women need more of during pregnancy. The Global Alliance for Improved Nutrition (GAIN) recently identified the top food sources for women of reproductive age. They assessed concentrations of iron, folate, zinc, vitamin A, calcium, and vitamin B12 in common food sources. To no surprise, they found that organ meats like liver and bivalves — like clams, mussels, and oysters — were found to have very high densities of micronutrients important for reproduction. This makes sense, as we know that “65% of dietary zinc comes from animal products such as meat, poultry eggs, oysters, and other seafood.” And that’s just one micronutrient.

While all shellfish are nutritious, bivalve shellfish are particularly nutrient-dense. In the GAIN’s analysis, bivalves scored just as high in iron, zinc, and vitamin B12 for micronutrient density compared with organ meats. They scored higher than kidney and heart organs for nutrient-density of vitamin A and calcium. All in all, these small shellfish pack a big nutritional punch with each bite. Check out the tables below to get a picture of the nutritional value of shellfish.

When you compare the zinc, iron and B12 content of commonly eaten proteins like chicken breast to oysters, you can see that oysters are off-the-charts high in zinc and several other micronutrients (see the image below).

Here’s how oysters compare to chicken breast (3 ounce serving of each):

Here’s how oysters, clams, and mussels compare to one of the most nutrient-dense foods on the planet: beef liver (ounce per ounce):

How the nutrients in shellfish support prenatal health

Below, I’ll detail a handful of the nutrients in shellfish and how they support your health during pregnancy & your baby’s development. Keep in mind that the GAIN analysis did not assess all micronutrients, so I’ll highlight a few additional nutrients that are also found in meaningful concentrations in shellfish, including copper, selenium, DHA, and taurine.

ZINC — Zinc is an important micronutrient during pregnancy as zinc deficiencies are linked to higher odds of miscarriage, preterm delivery, stillbirth, neural tube defects, and more. Plus zinc deficiency during pregnancy can adversely affect the long-term health of the baby and may predispose them to a higher risk for chronic disease later in life.

VITAMIN B12 — The vitamin B12 content of shellfish also deserves special mention. The number one richest food source of vitamin B12 are clams. Yes, clams contain even more vitamin B12 per ounce than liver. During pregnancy, B12 is a key player in fetal development as it is required for a process called methylation. Methylation is involved in gene expression, cell differentiation, and organ formation (you may recall that folate is also crucial to methylation). Without enough B12, there is an increased risk for neural tube defects, miscarriage, and preterm delivery.

IRON, COPPER, VITAMIN A — Shellfish are an excellent source of bioavailable heme iron. Clams, in particular, boast over 4-fold more iron than an equivalent portion of beef liver. Along with iron, most types of shellfish contain a complementary mineral: copper. Copper doesn’t get much attention in mainstream nutrition, but it’s vital to the metabolism and transport of iron. In fact, many of the nutrients in shellfish assist in iron metabolism and may be helpful in the prevention/mitigation of anemia; this includes vitamin B12, vitamin A, and copper. If you are struggling with anemia or iron dysregulation — and especially if you don’t eat much animal protein — incorporating shellfish into your diet can help! The vitamin A content of shellfish relative to liver is modest, but still contributes to overall intake (if you have questions about the safety of vitamin A or liver during pregnancy, read this article!).

SELENIUM — Seafood is one of the richest sources of selenium in our diet, and shellfish are no exception. Selenium has a wide range of functions in the human body, including supporting thyroid health, immune function, synthesis of DNA, detoxification, and fertility. Deficiency in selenium reduces levels of the liver’s major detoxification enzyme, glutathione, resulting in increased oxidative stress and impaired detoxification. Oxidative stress is a known contributor to poor egg and sperm quality. Low selenium status in pregnancy is a risk factor for miscarriage, low birth weight, and numerous pregnancy complications.

DHA — In addition to high concentrations of several vitamins and minerals, bivalve shellfish are rich in omega-3 fatty acids, including DHA, which is necessary for fetal brain and vision development. Shellfish typically feast on plankton, a concentrated source of DHA, which makes bivalves incredibly omega-3 dense  (“you are what you eat, right?”). In fact, the DHA content of many farmed and wild mussels, clams, and oysters is actually comparable to salmon, one of the most well-known omega-3 sources. If you’ve ever found yourself in a salmon rut (I know I’ve been there), know that there is an omega-3 equivalent in these delicious shellfish. 

TAURINE — Taurine, an amino acid, is another nutrient that bivalve shellfish are packed with. During pregnancy, taurine is a major contributor to normal fetal beta-cell development (pancreas), insulin action, brain development, eye development, reproduction, normal growth and development (especially bone growth), and antioxidant activity. Under normal physiological conditions, it is assumed that humans can make enough taurine from other amino acids to meet their needs. However, during pregnancy, taurine needs increase dramatically in order to provide sufficient amounts to the growing fetus making it “conditionally essential.” After birth, newborns also cannot synthesize adequate amounts of taurine and must rely on amounts found in breastmilk or formula. Naturally, this increased demand for taurine makes it ideal to obtain this nutrient from food. Bivalve shellfish (in addition to other seafood and organ meats) are a great option for sourcing this nutrient. 

Also be aware that taurine is only found in animal foods. If you otherwise don’t eat much (or any meat) or abstain from animal foods entirely for ethical reasons, there are some vegans who will make an exception to eat bivalve shellfish because they do not contain a central nervous system and therefore cannot experience pain. While the body can synthesize some taurine, this process is dependent upon vitamin B12, as outlined here. This means that deficiency in vitamin B12 — common on vegetarian, and especially vegan diets — can result in low taurine levels. Animal studies show that this scenario of low B12 and taurine can predispose animals to growth problems and osteoporosis. 

With all of the nutritional perks of shellfish, there’s good reasons to incorporate them into your diet! Although I’ve highlighted the prenatal benefits of including shellfish, many benefits can be extended into other life phases, including preconception/fertility and postpartum recovery. 

Do shellfish contain dangerous contaminants? What about heavy metals, like mercury and cadmium?

At this point, you might be thinking, “wait a second, aren’t you supposed to limit the amount of seafood consumed during pregnancy to avoid mercury?” 

This is a great question and one that I dive deep into in Chapter 3 of Real Food for Pregnancy. Many women are told not to consume fish or to limit it to no more than 12 ounces of fish per week out of fear that it will result in potentially toxic levels of mercury that could harm fetal brain development. While there are some fish that certainly should be avoided due to their mercury levels, they are typically very large fish like swordfish and king mackerel. In fact, the size of the fish is one of the best predictors of mercury levels. 

In short, 12 ounces of low-mercury seafood is perfectly safe and highly recommended to meet your nutrient requirements. Bivalves are considered small, low in mercury, and can safely be consumed while pregnant.

If you like shellfish, consider having 3-6 ounces of your weekly seafood intake from shellfish.

Now, one heavy metal that you may have also heard about is cadmium. Some fear that because shellfish can be a source of cadmium, it is not safe to consume. If you’ve ever seen a “Prop 65” warning on canned oysters, this is likely why. Proposition 65 is a very stringent California regulation on products sold in the state that may contain chemicals that could cause cancer, birth defects or other reproductive harm. It certainly sounds scary to read, but Prop 65 has an incredibly low threshold.

Although cadmium is found in shellfish, there have been some reassuring data published on its absorption and metabolism. Research indicates that 99% of cadmium ingested from shellfish is excreted. One study found that in women who ate shellfish once or more per week compared to women who ate a diet low in shellfish, their blood concentrations of cadmium were no different. Despite the shellfish group consuming twice as much cadmium per week compared to those in the low shellfish diet, there were no statistically significant differences in cadmium concentrations in the blood levels of the two groups. Additionally, researchers measured the amount of cadmium in their stool and found low average absorption of dietary cadmium. 

A diet rich in zinc and selenium (and other minerals) seems to protect against cadmium accumulation in the body (which thankfully oysters and other shellfish contain in ample quantities). Like all foods, you have to weigh the risk/benefit and only you can decide what you’re comfortable with. You can argue toxins for avoidance of many foods, like rice or chicken & arsenic, acrylamides & browned potatoes/starches, etc. Every food has trade offs.

To me, the nutrient density of shellfish and high content of beneficial minerals that offsets concerns about heavy metal exposure.

Food safety: Can you eat raw shellfish or raw oysters in pregnancy?

In Real Food for Pregnancy, I discuss the controversy around consuming raw seafood during pregnancy. Oftentimes the benefits of raw seafood outweigh the risks (see chapter 4). However, raw shellfish does carry higher risks of food poisoning.

Out of all foodborne illness cases in the U.S. related to seafood, 75% are from the consumption of raw shellfish. Unless you’re 100% certain that the raw oysters you’re getting are super fresh and have been handled properly, you’re better off eating cooked shellfish.

Again, this is a personal risk:benefit decision that you can make for yourself. Having lived in some of the major shellfish harvesting areas in the country, I know plenty of people who consume raw shellfish regularly without ever getting sick (probably because they are so fresh and haven’t traveled thousands of miles before being consumed). Like all food safety decisions, no choice is black and white. How the food is grown, raised, harvested, and handled prior to consumption is paramount.

Many of you who do not live coastally have asked me about canned smoked oysters. If you are eating canned oysters, it is OK to consume them straight from the can without reheating since the canning process uses sufficient heat to kill any bacteria or other microbes. Any blanket food safety recommendations over smoked seafood consumption in pregnancy are technically related to raw smoked seafood, not canned smoked seafood. Again, I cover the relative “riskiness” of consuming raw seafood in chapter 4 of Real Food for Pregnancy.

Tips for including more shellfish in the diet

By now, I hope you’ve seen how incredibly nutrient-dense and beneficial shellfish can be for you and your growing baby. But if shellfish are not currently part of your regular diet, if you don’t live somewhere with access to fresh seafood, or if you’ve never tried them before, you may be feeling a little lost on where to start to incorporate shellfish into your diet. 

First off, let me reassure you that eating shellfish does not have to be an everyday food (much like liver). 

One to two servings (3-6 ounces) per week is enough to reap the nutritional benefits of shellfish. If you live in a place where seafood restaurants or fish markets are common, plan a date out and order shellfish or try a new recipe and make it yourself! 

Meals/snack ideas that contain shellfish:

• Clam chowder (it’s very easy to make using canned clams)
• Steamed clams
• Mussels with broth
• Seafood stew or curry
• Seafood paella
• Canned oysters (see below)

If you live somewhere more land-locked, or if you’re looking for quick ways to incorporate shellfish into your diet as a snack or meal, consider purchasing canned, smoked oysters. The flavor is rich & smokey and the texture is soft (very different from raw oysters, but I think both are delicious). Next time you see some at the store, pick up a can. My favorite is one by Crown Prince where the oysters are canned in olive oil – yum! (No affiliation, I just link this brand.) I find these at Trader Joe’s, but some health food stores may have them, too. Canned shellfish is delicious straight out of the package or you can eat them on top of a plantain chip or cracker with a little cream cheese. Check out this Instagram post to see how I do it.

If you cannot find smoked oysters canned in good quality oil, yes, I think they’re still worth eating if they’re canned in vegetable/soy oil. Just drain the extra oil/blot on a paper towel. Don’t let nutritional perfection keep you away. Although I don’t encourage lots of refined vegetable oils (see Ch 4 of ​​Real Food for Pregnancy to understand why), half a gram of residual omega-6 fat will not kill you, my friend.

Another option is to check the frozen section of your grocery store. There are often packages of pre-cooked, de-shelled mussels and clams, which can be added to curry, soup, or a pasta dish. They simply need to be reheated, so it’s a very quick addition to meals. The flavor and texture isn’t quite as good as restaurant mussels, but it’ll do in a pinch.

Summary

• Shellfish are creatures like shrimp, lobsters, and clams that contain many nutrients that are beneficial to pregnancy 
• Clams, oysters, and mussels are a type of shellfish called bivalves that are particularly nutrient-dense in zinc, iron, vitamin B12, and several other nutrients.
• Bivalve shellfish are comparable in nutrient density to organ meats like liver, kidney, and heart. 
• Bivalve shellfish are also rich in omega-3 fatty acids and taurine, two nutrients that are critical to fetal development, particularly fetal brain development
• Shellfish are lower in mercury than larger aquatic animals, and while they do contain cadmium, studies have shown that the limited absorption of cadmium from shellfish makes them safe to eat in moderation. 
• During pregnancy, there are food safety considerations with shellfish consumed raw. 
• You can include more shellfish in your diet by eating more clam chowder, steamed clams, or seafood stew. Or, choose canned oysters for a quick and easy snack or meal. 

Until next time,

Lily

PS – Will you be having shellfish for dinner? I think I will! Let me know your favorite ways to eat shellfish in the comments below.

 

References

 

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