These days it’s hard to miss the packs of crunchy seaweed snacks, umami seasonings, and sushi rolls. Seaweed has skyrocketed as a food trend over the past few years, and for good reason.
The nautical leafy green vegetable is a budget-friendly snack choice, ups the flavor ante in meals, and is rich in essential vitamins and minerals- especially those important for healthy fetal growth development.
But can there be too much of a good thing while pregnant?
Seaweeds are a rich source of nutrients such as iodine, making them a good choice during pregnancy. However, some varieties of seaweeds may contain an excess of iodine and should be eaten in moderation when you’re pregnant.
From the nori used for wrapping sushi and the green variety found in salads to chewy brown seaweed used in soups, read on to find out which types of seaweeds are safe, when and how to eat them, as well as, how much seaweed you can eat safely when pregnant.
Is Seaweed Safe During Pregnancy?
“Seaweed” is a fairly generic term that refers to marine algae, regardless of color or official sub-type of the species (source: American Scientist).
Seaweed is generally considered safe for consumption during pregnancy. Even though seaweeds can have many nutritional benefits for pregnant women, some types of seaweed should only be eaten in moderation.
The seaweed we see sold in stores is categorized based on the official scientific plant family which it belongs to, rather than its color – but you’ll need to know which is which in order to eat it safely during pregnancy.
Here’s a guide to each type, and how safe they are to eat when pregnant:
Brown seaweed is the main type to watch out for during pregnancy, as it has a much higher iodine content compared to red and green types. Examples of brown seaweeds are:
- Arame (also called ‘sea oak’)
- Wakame (see ‘seaweed salad’ later in this article)
- Kombu – often used to make Japanese Dashi stock
- Hijiki – which may also have higher than normal levels of arsenic (source: IJMS).
Although iodine is certainly needed during pregnancy, too much iodine can lead to poor thyroid function, which can lead to poor fetal thyroid function as well (source: Nature Reviews Endocrinology).
For this reason, both the British Dietetic Association and Food Standards Australia/New Zealand recommend that pregnant women eat no more than one (1) ¼-cup serving (around 32g) of brown seaweed per week (source: BDA, FSA/NZ).
How you prepare seaweed can also impact how much iodine you consume, as boiling seaweeds such as kelp can reduce the amount of iodine by up to 90%, though this is transferred to the stock it’s boiled in (source: TRJ).
Kelp, in particular, has higher amounts of iodine than other kinds of seaweed. Pregnant women should steer clear of supplements containing kelp (source: NCBI). Kelp in foods can still be eaten up to once a week.
Red seaweed is one you might come across often, even though it looks green! Red seaweed includes:
- Nori – the flat sheets that are used for making sushi and onigiri.
- Dulse – a chewy reddish-brown seaweed used in stews and soups
- Purple laver
- Irish moss
Bear in mind that green nori is either red seaweed with food coloring or a green seaweed, pretending to be nori!
Red seaweeds are safe during pregnancy and can be eaten more often than brown seaweed. It also has many benefits in pregnancy, which we’ll cover later in this article.
Green seaweed includes:
- Ulva or sea-lettuce – usually used to make salads and soups
- Sea grapes
- “green caviar” – just a nickname, it’s not actually caviar
Like red seaweed, green seaweed is also pregnancy-safe and can offer several benefits for pregnant women (source: PMC).
The Benefits of Eating Seaweed During Pregnancy
With an abundance of health benefits, seaweed is a great addition to your diet during pregnancy (source: PubMed).
The protein present in some seaweeds, such as spirulina and chlorella, contains all of the essential amino acids (source: NCBI).
Seaweed is an excellent source of vitamin B12, which is especially crucial if you’re vegan or vegetarian as it’s one of the few non-animal sources (source: Nutrients Journal).
Seaweed is a good source of several minerals, including calcium, copper, iodine, magnesium, phosphorus, potassium, and zinc (source: Food and Nutrition).
The iodine level in seaweed, mainly brown seaweed, helps promote healthy thyroid activity, while the iron is essential for hemoglobin production during pregnancy (source: PMC).
As previously mentioned, brown seaweed is best limited to once a week, though the iodine it contains is still essential during pregnancy.
Adequate iodine intake helps prevent neurological impairment in the developing baby and positively impacts the baby’s cognitive skills (source: WHO). Brown seaweeds also have anti-inflammatory properties that help reduce joint and muscle pain (source: PMC).
Seaweeds are also excellent sources of fiber, which is known for helping with common pregnancy ailments such as constipation and other digestive problems (Source: Gut Microbes Journal).
A study conducted on Japanese women confirmed that seaweed consumption during pregnancy could reduce the risk of depressive symptoms in women to a considerable extent (source: PMC).
How Much Mercury is in Seaweed?
Overall, the amount of mercury in seaweed is quite low, and therefore shouldn’t be a concern during pregnancy.
That said, the amount of mercury in seaweed varies depending on the type of seaweed it is. For example, a study in Nature found that mercury levels are significantly lower in red seaweeds than brown ones (source: Nature Journal).
Organic seaweed contained the least amount of mercury and other toxic elements, so you might want to choose organic seaweed throughout pregnancy.
Another 2010 study tested 426 samples of store-bought edible seaweed for their mercury content. The research found the average mercury content of food-grade seaweed was 0.01 mg/kg dry weight.
Compare this to the 0.126 mg/kg average mercury in canned light tuna, which the FDA recommends 2-3 servings per week for pregnant women (source: FDA)
The verdict? Seaweed does contain mercury, but still less than the acceptable level in a serving of canned light tuna.
The overall mercury levels in seaweed are, according to WHO, safe for human consumption, even in places like Korea, where seaweed is consumed daily (Source: PubMed.gov).
That means that even if you eat a LOT of seaweed, you wouldn’t ingest enough mercury to impose any significant health risks for you and your baby.
As an aside, certain seaweeds such as hijiki and kombu contain traces of arsenic (source: IJMS) but, again, these are usually not in high enough levels to be of concern during pregnancy, though you may choose to avoid them.
Can Pregnant Women Eat Seaweed Salad?
Seaweed salads can be a good addition to your pregnancy diet because of the abundance of nutrients they provide.
Seaweed salads are usually made with wakame, though some use hijiki, kelp, ogonori, or red dulse seaweed. Amongst these, the first three belong to the category of brown seaweeds – the ones that should be eaten moderately when pregnant (source: BMJ).
This means that it’s probably best to eat seaweed salad a maximum of once a week during pregnancy if it’s made with one of these seaweeds.
Seaweed salad is not only low in calories, but it’s also a great source of vitamins A, B, C, E, and K. In fact, seaweed salad is one of the few vegetarian foods rich in vitamin B12 (source: PubMed).
If you’re pregnant and follow a plant-based diet, seaweed salad can have extra benefits, as it offers almost six grams of protein in each eight-ounce raw serving, along with a healthy dose of folate (15% DRI), which is crucial for expectant women (source: NutritionData).
It would also be a great source of fatty acids for pregnant women following a plant-based diet, as most Omega-3 supplements are fish-oil based.
However, bear in mind that seaweed salad can also be very high in sodium. 1 cup of seaweed salad can give as much as half the RDA for your sodium intake: 900-1200 mg (source: NutritionData), so check this if you’re following a low sodium diet.
Seaweed Dishes and Pregnancy Safety
It can be challenging to identify the type of seaweed that packaged seaweed snacks are made from.
In most cases, the packaging just says “seaweed”, which is unfortunately not very helpful if you are a pregnant woman trying to watch out for brown seaweed!
Roasted seaweed sheets and crisps are usually either nori, dulse, or kombu. If you aren’t sure, it can be a good idea to limit your snacking to once a week.
Popular brands like Annie Chun’s are made from nori. The gimMe Organic brand also has a wide range of acceptable nori sheets and seaweed snacks, many of which are also gluten-free.
Seaweed snacks are safe for pregnant women to consume; the only reason you may need to moderate your intake is if your medical professional has recommended a low-sodium diet.
Seaweed naturally contains sodium (as does nearly every food in the world), but added salt could lead to high blood pressure, especially if you are already considered “at risk”.
Restricting salt during pregnancy isn’t necessary for most women, but it’s wise to follow the Dietary Guidelines for Americans and keep sodium consumption under 2,300 mg/day. Seaweed snacks are VERY easy to overconsume, so bear this in mind.
Seaweed in Soup
Seaweed is most commonly found in miso soup and other similar Asian dishes.
The amount of seaweed in soup is usually pretty small, so it’s usually safe to eat during pregnancy. This is usually green seaweed, but can sometimes be brown seaweed such as kelp.
Miso soup has many health benefits, including folic acid, and fermented ingredients, which are beneficial for the gut.
If you’re a fan of miso soup, then you’ll probably be interested in our guide to the benefits of miso soup during pregnancy.
Seaweed in Sushi
The seaweed used in sushi (like hand rolls, maki or temaki) is almost always nori, and is therefore safe during pregnancy.
Nori, or sushi seaweed, is also very nutritious, without the same high levels of iodeine that brown seaweed has.
Tip: If you plan to eat sushi during pregnancy then you’ll want to check out our safety guide to sushi when you’re pregnant – it’s got everything you need, including a ‘safe’ menu list.
Roasted seaweed is often just another name for nori sheets (used in sushi, as described above) or seaweed snacks, which were also covered earlier in this article. Most roasted seaweed is therefore safe for pregnant women.
Aonori is its powdered form, used as a condiment for flavoring traditional Japanese dishes like okonomiyaki (pancakes) and yakisoba (buckwheat noodles).
If it’s flavored – as many roasted sheets of nori are – then again, check the sodium content if you have to watch your salt intake, as many flavorings/powders increase this even further.
Dried Seaweed (seaweed sprinkles)
Furikake (Japanese for “sprinkle over) seasoning is usually added to steamed rice, avocado, or anything else that could use a flavor boost.
It’s made from a mixture of dried crushed seaweed (usually nori, kelp or dulse), sesame seeds, salt, and other herbs or spices. Seaweed sprinkles are safe to consume during pregnancy.
It’s a great way to flavor dishes that might need a little more depth, and not to mention looks very social-media worthy when sprinkled over a perfect avo toast.
The only reason to avoid this seasoning is if there is an ingredient to which you might be allergic; if you are concerned about that, check the label or skip it.
If you are trying to limit salt, check the sodium content or double-check with your medical provider that it’s safe to consume; however, the amount that you would eat is probably not high enough to be a concern for either iodine or sodium.
The brand Numami stocks organic kelp or wakame flakes that are grown in the Atlantic and are USDA-certified. They are freeze-dried rather than fried in oil and salt.
Kombu and wakame are usually eaten raw if they’re in a seaweed salad. Keep in mind that kombu and wakame are brown seaweeds, so eat them in moderation during pregnancy.
Most other seaweed is eaten after it’s been dried or roasted. However, it is safe to eat fresh, raw marine seaweed during pregnancy, with a few limitations.
Like any food that is often foraged, you’ll need to be sure of both the seaweed’s identity and its source. It’s also important to make sure that the water that the seaweed has been living in is not contaminated with chemicals or high levels of heavy metals.
If there is a question about the source of the raw seaweed, it might be best to skip it.
However, if you are sure that it’s coming from a trusted area, raw seaweed is a fantastic wrap for sandwiches or even a substitute for cabbage in a cabbage roll.
Other ways to incorporate raw seaweed would be as a substitute for lettuce or as an addition to a salad.
Although called crispy seaweed, this food is not seaweed at all, but deep-fried greens such as kale or cabbage.
It’s a popular Chinese dish, often garnished with sesame seeds, Chinese five-spice powder, chili or simply sprinkled with salt.
You don’t have to check for heavy metals or iodine with crispy seaweed, though it’s a good idea to limit deep-fried foods for general health reasons.
The only reason to avoid this dish during pregnancy is if there is a vegetable to which you are allergic, or don’t tend to care to eat.
Overall, seaweed packs a nutritious punch and can definitely be a valuable part of your diet during pregnancy. Knowing the type of seaweed you’re eating is a good precaution, as you should enjoy brown seaweed in moderation, limiting to ¼-cup (around 32g) each week to avoid excess iodine.