You might have already seen seaweed at your favorite sushi place. But have you ever wondered why it is used and if there are any health benefits to it? This post will show you 7 benefits of kelp and other seaweeds but also some downsides to these sea vegetables.
What is seaweed?
If you were wondering, no it doesn’t get you high. But there are many other benefits to it. So what are seaweeds like kelp or nori? Just like on land there are tons of different plants growing under water, including seaweed or algae (although they are not clearly classified as plants).
Edible seaweed can be divided into four categories:
- Brown algae (such as Kelp or Wakame)
- Red algae (such as Nori or Dulse)
- Green algae (such as Sea Lettuce)
- Blue-green algae (such as Spirulina)
These seaweeds have a long history in Asian countries where they play a major role in local cuisine. Only recently have they found their way into the Western cuisine. What are the reasons to include seaweed into our diet?
7 benefits of kelp and other seaweed
Kelp, nori and other seaweeds are very nutrient-dense because they are packed with dietary fiber, o-3 fatty acids, essential amino acids, iodine and vitamins A, B, C, and E.
1. Fiber and digestion
Similar to other plant foods seaweeds are a rich source of dietary fiber (25-75% dry weight). These polysaccharides, namely alginates, carrageenans, cellulose and agars found in kelp and other seaweeds aid digestion. Studies also indicate that these fibers increase gut health and that alginate, in particular, could help to fight obesity since it reduces the body’s fat uptake.
2. Protein and amino acid profile
In general, seaweed protein contains all essential amino acids and is high in glycine, arginine, alanine and glutamic acid. However, lysine and cystine contents are fairly limited. (Check out my post about lysine for high-lysine plant food alternatives) But although, most edible seaweeds provide a good source of protein the recommended serving sizes are too small to make up a good portion of your daily protein intake. 
3. Healthy fats
Kelp, Nori, and other seaweeds have a very low-fat content ranging from 1-5% of dry matter. The proportion of essential fatty acids such as omega-3 and omega-6 fatty acids is higher than that in terrestrial plants.  These types of fat help to raise healthy HDL cholesterol levels while lowering harmful LDL cholesterol levels. They furthermore have an anti-inflammatory effect which might reduce the risk of cardiovascular disease.
Both water-soluble vitamins such as vitamin B and C and lipid soluble vitamins such as vitamin A and E can be found in seaweed at varying levels. Some of the concentrations of vitamin A, E and C are even higher compared to their terrestrial counterparts. Some research indicates that a few seaweeds such as Chlorella contain vitamin B12, but in my opinion, studies are still too vague to rely on them as an essential source for vitamin B12.
5. Iodine and other minerals
Almost all of the minerals found in the ocean are also found in seaweed. That’s why Kelp, Nori, and other seaweeds are packed with minerals. The mineral content can vary between different seaweeds but generally, they contain considerably high amounts of iron, copper, magnesium, calcium and of course iodine. Most seaweeds are a primary source of iodine, and in some seaweed, iodine content even exceeds the RDA of 150 μg/day. However, iodine content in different seaweeds ranges from 16 μg/g to even 8000 μg/g. This not only depends on the type of seaweed but also varies on the geographic location the seaweed was harvested from. Generally, the highest iodine content is found in brown algae such as kelp or kombu, and in most instances, red and green algae such as nori have lower contents. These factors make seaweeds one of the best plant-based foods to fulfill iodine requirements of humans.
6. Reduction of cancer risks
Studies found out that seaweed also reduces the risk of certain cancers. In particular, research states that kelp, nori and other seaweeds have positive effects on the prevention of colorectal cancer and breast cancer. Especially diets high in red and processed meat, as well as low fiber intake, are associated with an increased risk of colorectal cancer. The fiber from seaweed enhances water binding in the gut and traps toxins and other cancerous material in the digested food. Another study attributed the lower rate of breast cancer in Japanese women compared to American women to the fact that brown seaweed intake contributes to lower hormone-dependent cancer rates.
As mentioned above seaweeds contain many different vitamins. These vitamins, especially vitamins E, C and carotenoids a precursor to vitamin A make seaweed a good source of antioxidant compounds. These compounds may help protect cell damage caused by free radicals and therefore may prevent diseases such as cancers and Alzheimer’s.
Kelp and other seaweeds, too healthy to be true?
Now that we have talked about the benefits of seaweed, let’s take a look at some of the downsides and potential risks of consuming excessive amounts of seaweed.
Heavy metals in seaweed
Since the sea for seaweed is like the soil for terrestrial plants the seaweed will absorb what is in the water may it be good or bad. Kelp, nori and other seaweeds can contain toxic metals such as lead, mercury, and arsenic. As with the nutrient content, this likely depends on the type of seaweed, where it is from, and the levels of toxic metals in the water. Two Korean studies of seaweeds confirmed a low probability of health risks from heavy metals found in seaweeds, whereas a Spanish study didn’t paint such a nice picture and states that more research has yet to be done. If you want to be safe, buy your seaweed from providers that publish regular lab tests.
Regardless of the provider, you should definitely stay away from hijiki. Several studies indicate that hijiki contains arsenic which exceeds safety limits. And the UK Food Standards Agency (FSA) even issued advice to consumers to avoid eating it.
Too much iodine?!
As the founder of toxicology Paracelsus put it:
All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy.
What is of special interest in this context is iodine for which seaweed is a primary source. As you can imagine too little iodine is harmful which can lead to thyroid disorders. But vice versa consuming excessive amounts of iodine is also harmful and no good for your thyroid.
As with most things in life, moderation is key here. You can include seaweeds with lower iodine contents such as nori, wakame or dulse a few times a week. For higher iodine seaweeds which are mostly found in brown seaweeds such as kelp or kombu, however, I would recommend to only consume once in a while.
Iodine intake in Asia and goitrogenic foods
What is furthermore interesting regarding this topic is that your thyroid might adapt to iodine levels. A study shows how people in Japan and Korea, which habitually include seaweeds into their diets, could be relatively immune to negative effects of high iodine intake, but one of these single seaweed-rich meals could already present health risks to unhabituated people in low-iodine consuming countries.
On the other hand, this might also be explained by the fact that Asian cuisines typically serve seaweed together with goitrogenic foods such as broccoli, cabbage, bok choi, and soy. The phytochemicals in these foods can inhibit iodine uptake by your thyroid gland.
This doesn’t mean Asian cultures don’t suffer from thyroid disorders. Transient hypothyroidism and iodine-induced goiter is common in Japan and can be reversed in most cases by restricting seaweed intake.
Keep in mind that the safe dose of iodine may depend on the kind of seaweed, but also the storage conditions, cooking methods, the climate where the person resides, the amount of physical exercise a person does, the presence of goitrogenic foods eaten with the meal, and the frequency of seaweed consumption.
So to conclude this post. Seaweed is great mainly for its iodine content as well as for other essential nutrients listed above. However, consuming excessive amounts of seaweeds can be harmful to the body since the maximum daily intake of iodine is reached with fairly small amounts.
Regarding most of the other essential nutrients mentioned above, serving sizes are often not large enough to get a decent boost.
Considering this information kelp, nori and other seaweeds, unfortunately, aren’t a realistic source of many vitamins, but their high iodine content makes them a good plant-based alternative to iodized salt and other iodine fortified foods for vegans.
I hope you enjoyed this post! If you did, feel free to share.
Peace and take care!
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