Sea Vegetables | Oceans of Nutrients

WRITTEN BY TRANG TRAN AND DR. SWATHI

Southeast Asian countries such as Korea, Japan, and parts of China consume the greatest proportion of seaweed, also known as marine algae. Although seaweed is gaining popularity in Western countries, the majority of seaweed is used in the manufacture of gelling agents in the food, pharmaceutical, and cosmetic industries. 

Seaweeds are classified into three types based on their pigment content: red algae, brown algae, and green algae. Similar to terrestrial plants, marine algae are also rich in carbohydrates, proteins, lipids, and vitamins.

What are the types of sea vegetables?

In short, a few types are wakame, agar, nori, kombu, and dulse. Let's dive in.

Wakame

The traditional Japanese diet consists of wakame, which is typically consumed with noodles, soups, salads, or pickles. Not only does wakame exhibit blood-pressure lowering effects as mentioned previously, but it also helps prevent metabolic disorders when given as a supplement in clinical trials. Alginate, the primary dietary fiber in  wakame, has been reported to reduce glucose uptake. Dried wakame typically comes in the form of strips that are shriveled up.

Agar

Agar is composed of two polysaccharides, namely, agarose and agaropectin. It is soluble in hot water, and the solution forms a gel at around 32-40 °C, which then does not melt below 85 °C. With similar uses as carrageenans, agar is often used as a stabilizing agent or gelling agent and for maintaining viscosity. Commercially, agar is available as powder or flakes. 

Nori

Also known as purple laver, nori, in its dried form contains numerous nutrients including vitamin B12, which is the sole vitamin absent from plant-derived food sources. Thus, nori appears to be a suitable source of B12 for vegetarians. However, the bioavailability of B12 in nori is unclear. Nori is generally used to make sushi or rice balls in Japan. Another way of eating nori is to add it to vegetable soup. Dried nori sheets are commercially available and become crispy after being toasted or roasted.

Kombu

Kombu is a type of kelp that is used in making dashi (soup stock) as well as a seasoning for rice. Notably, it is added to beans when cooking to help reduce gas. It is available as dry, pickled, or fresh.

Dulse

Dulse resembles a red leafy lettuce and possesses a salty taste. It is typically available as dried, flaked, or as a powder or part of seasoning mixes. One of our favorite uses of dulse is in this recipe for a showstopping vegan caesar salad.

What are the health benefits of seaweed?

Heart health 

The carotenoid fucoxanthin found in wakame, which is a brown seaweed, was shown to reduce blood pressure and stroke risk factors in rat models. Apart from reducing blood pressure, fucoxanthin may also help with weight management by upregulating the process of fat breakdown. Through its antioxidant activity, fucoxanthin may also have potential as a food preservative for meat. In a study involving individuals with diabetes, agar (a type of carbohydrate from red seaweed that is used as a gelling agent) consumption in addition to conventional diet and exercise routine for 12 weeks significantly reduced body weight, body mass index, and total cholesterol levels when compared with diet and exercise alone.

Furthermore, fucoidan extracted from brown seaweeds has shown blood thinning properties that may help prevent cardiovascular disease. Moreover, laminarin isolated from brown seaweeds have been reported to exhibit antioxidant, anti-inflammatory, as well as blood thinning properties.

Because seaweeds contain good sources of long-chain omega-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), they may have beneficial properties relevant to heart disease.

Digestive health

Compared to terrestrial vegetables, seaweeds have a similar or slightly elevated levels of total fiber. Fibers can increase feelings of satiety and aid digestive transit through bulking capacity. In fact, nori (which belongs in the red seaweeds category and are the ones that are used in sushi) contains slightly more fiber than bananas in direct weight comparisons although the amount consumed in the diet would be lower. Compared to brown rice, kombu (a type of brown seaweed) shows a higher level of total fiber; kombu also has a balance of soluble and insoluble fibers.

Additionally, storage polysaccharides (carbohydrates) such as alginates, carrageenans, and agar from seaweed serve as prebiotic (also known as food for the beneficial gut bacteria).

Anti-cancer

Nori contains a bioactive molecule called porphyrin that was attributed to lowering the probability of breast cancer.

Bone health

Because minerals are gathered from seawater, this makes seaweed rich in minerals such as calcium, magnesium, sodium, phosphorus, zinc, and iodide. A higher intake of foods containing seaweed has been associated with adequate calcium intake to prevent osteoporosis in Korean postmenopausal women. Interestingly, the calcium content of kombu exceeds that of whole milk on a weight/weight basis. However, seaweeds also accumulate undesirable minerals from the environment, raising safety concerns for human consumption.

Are sea vegetables safe?

Given that a 5-g portion of kombu can provide up to 0.35 g of salt and 0.26 g of sodium, whereas dulse can provide up to 0.27 g of salt and 0.15 g of sodium, it is important to have small portion sizes of seaweed to prevent excessive salt intake. 

Seaweed is also rich in iodine and several studies have shown that high consumption of iodine-containing seaweeds can interfere with normal thyroid function, causing both hyperthyroidism and hypothyroidism.

Another concern with seaweed consumption is exposure to heavy metals (e.g., arsenic, aluminum, cadmium, lead, rubidium, silicon, strontium, and tin) due to contamination caused by industry and poor sewage systems. 

The bottom line

Seaweeds are marine aquatic vegetables that are rich in nutrients, containing bioactive compounds and  omega-3 fatty acids that contribute to heart health. The high fiber content provides digestive health benefits, and the high mineral content contributes to bone health. Due to the salt and iodine content and the possible exposure to heavy metals, seaweed should be consumed in moderation. There are different kinds of edible seaweeds, each with various culinary uses.

 

References: 

1. Bito T, Teng F, Watanabe F. Bioactive Compounds of Edible Purple Laver Porphyra sp. (Nori). J Agric Food Chem. 2017;65(49):10685-10692. doi:10.1021/acs.jafc.7b04688
2. Brown ES, Allsopp PJ, Magee PJ, et al. Seaweed and human health. Nutr Rev. 2014;72(3):205-216. doi:10.1111/nure.12091
3. Cherry P, O'Hara C, Magee PJ, et al. Risks and benefits of consuming edible seaweeds. Nutr Rev. 2019;77(5):307-329. doi:10.1093/nutrit/nuy066
4. Lozano Muñoz I, Díaz NF. Minerals in edible seaweed: health benefits and food safety issues [published online ahead of print, 2020 Nov 18]. Crit Rev Food Sci Nutr. 2020;1-16. doi:10.1080/10408398.2020.1844637
5. Rajapakse N, Kim SK. Nutritional and digestive health benefits of seaweed. Adv Food Nutr Res. 2011;64:17-28. doi:10.1016/B978-0-12-387669-0.00002-8
6. Tanna B, Mishra A. Nutraceutical Potential of Seaweed Polysaccharides: Structure, Bioactivity, Safety, and Toxicity. Compr Rev Food Sci Food Saf. 2019;18(3):817-831. doi:10.1111/1541-4337.12441
7. Yoshinaga K, Mitamura R. Effects of Undaria pinnatifida (Wakame) on Postprandial Glycemia and Insulin Levels in Humans: a Randomized Crossover Trial. Plant Foods Hum Nutr. 2019;74(4):461-467. doi:10.1007/s11130-019-00763-5

 

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This article was edited by Dr. Swathi and was written by Element Apothec Scientific Communications Intern, Trang Tran. She is a Doctor of Pharmacy (PharmD) student at Oregon State University and Oregon Health & Science University College of Pharmacy in Portland, Oregon.