Health benefits of seaweed: Edible varieties and where to buy it

Author: Rosie Martin

Read Time:   |  4th October 2022

Seaweed has been used been used as a food source for millennia but has surged in popularity in recent years thanks to its myriad of health benefits. Here we dive in to learn more about the health benefits of seaweed and why you should consider adding it to your vegan diet...

Edible seaweed, often referred to as sea vegetables, refers to marine algae that can be consumed by humans. Although seaweed has been utilised as a food source for millennia, it has regained popularity in recent decades for use in dishes such as salads, sushi, and snacks.

Edible seaweeds can be categorised based on their chemical and nutritional make-up. The main categories are red, brown, and green algae, as well as single-celled microalgae you may have heard of such as chlorella or spirulina1. 

Is seaweed good for you?

Sea vegetables are a low-energy, nutrient-rich plant food. Seaweed contains good levels of dietary fibre, plant-based protein, vitamins, and minerals, as well as bioactive plant compounds that support health over and above the nutrients they contain.

Seaweed has been found to contain high levels of polyphenolic compounds including catechin, and gallic acid.

Polyphenols provide health benefits through antioxidant, anti-cancer, anti-viral and anti-inflammatory properties that contribute to reduced risk of heart disease, death from cancer and a longer life expectancy2. 

Fibre is an over-looked and under-consumed component of plant food. Seaweed provides both soluble and insoluble forms that promote beneficial gut bacteria, add faecal bulk and reduce transit time, making them crucial for good gut health.

Seaweed is a high-fibre food and can contain between 29g and 62g of fibre per 100g of dry weight; a range that is higher than many terrestrial fruits and vegetables3.

Although protein content varies, seaweed can contain up to 47% protein based on dry weight4. Nori, a type of red seaweed, generally provides the most. The protein content of seaweed varies across the season however, and how well humans can absorb and use this protein remains unclear3. 

Seaweed is packed with health benefits because it contains high levels of dietary fibre, plant-based protein, vitamins, and minerals. Image credit: Darren Lehane vis Getty Images

Seaweed is packed with health benefits because it contains high levels of dietary fibre, plant-based protein, vitamins, and minerals. Image credit: Darren Lehane vis Getty Images

Sea vegetables are a low-fat food, with a fatty acid content of around 1-5% of dry weight. The main types of fatty acids found in seaweed are polyunsaturated, with a beneficial ratio of around 1:1 omega-3 to omega-63. Seaweed also contains the beneficial omega-3s eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Fish are readily promoted as good sources of these EPA and DHA fatty acids however they obtain these through consumption of seaweed. Going back to the original source by taking algae-derived omega-3 supplementation provides a sustainable alternative.

Seaweed contains high levels of minerals which can contribute up to 36% of its dry weight. The level of minerals in seaweed depends on the marine environment in which it grows3. Seaweed can be particularly high in calcium, iron, copper, magnesium, and iodine.

What are the benefits of seaweed for vegans in particular?

Seaweed may be a particularly beneficial food to include as part of a vegan diet due to the omega-3 fatty acids and iodine it contains.

Those on a vegan diet can obtain the omega-3 fatty acid alpha-linolenic acid (ALA) from walnuts and flaxseeds, which can then be converted into the previously mentioned EPA and DHA in our bodies.

Unfortunately, this process may be slow, and so using algae-based supplements may be a wise decision for those on a vegan diet.

Iodine is an often-forgotten nutrient, despite high levels of deficiency found in many population groups. Young girls and pregnant women are particularly at risk, which is concerning as iodine is crucial for the development of a baby’s brain through pregnancy6.

Seaweed is a rich source of iodine, however it is important understand the best types of seaweed to consume, as having too much can have health issues of its own; pregnant women are not recommended to consume seaweed more than once a week for this reason6. 

Pregnant women are recommended to consume seaweed no more than once a week because it is so rich in iodine. Image credit: d3sign via Getty Images

Pregnant women are recommended to consume seaweed no more than once a week because it is so rich in iodine. Image credit: d3sign via Getty Images

To make matters more complicated, the iodine content varies between the same seaweed growing in different areas, the iodine content is often not stated on food packaging, and we don’t have a clear answer as to how much of the iodine is absorbed by the body. This is an area in which we await further research.

Having said this, dried nori is one of the most common types of seaweed available in the UK. Based on current data, nori provides around 42µg of iodine per 2g sheet, which is roughly a third of the recommended intake.

Kelp on the other hand could provide 1327µg of iodine in just one gram, which is over twice the upper safe limit7. An easy alternative to navigate this area, particularly if you don’t consume seaweed, is to take a daily non-seaweed supplement of 150µg to cover your daily iodine needs.

Is seaweed a vegetable?

Biologically speaking, plants and algae are different types of living organisms, but in terms of their use in nutrition, they can be considered a type of sea vegetable.

Which types of seaweed are edible/should you cook with?

There are many types of edible seaweed. The most common ones you may find in the supermarkets or on restaurant menus are nori, kombu, wakame, dulse, Irish moss, and sea lettuce.

You can try adding seaweed to your diet today by making this delicious tofish recipe with chips, a vegan take on the classic fish and chips.

If you forage for you own seaweed, ensure you go with an expert so you are certain that you only consume seaweed that is safe.

What is crispy seaweed? Is it seaweed?

Despite the misleading name, the Asian side dish ‘crispy seaweed’ is made using spring greens or kale rather than seaweed.

Despite its name, crispy seaweed is actually made from spring greens or kale. Image credit: Quanthem via Getty Images

Despite its name, crispy seaweed is actually made from spring greens or kale. Image credit: Quanthem via Getty Images

What else should we consider when adding seaweed into our diet?

There is ongoing research into the potential high levels of heavy metals such as inorganic arsenic, mercury and cadmium in seaweed that may be detrimental to health.

At the current time, the UK Food Standards Agency advise against consuming hijiki seaweed due to high levels of inorganic arsenic that may increase risk of cancer8.

Where to buy seaweed

Seaweed is becoming increasingly available on the UK market as an ingredient in snacks, sushi, and even formed into noodles. It is best to find those with the nutritional content stated on the packet, however this is often more difficult to find. Aim to buy seaweed or seaweed products that have been sustainably and responsibly harvested.

Seaweed can be an excellent addition to the diet. Just be careful to choose the right type and consume in small to moderate quantities. Sea vegetables can bring a delicious savoury or ‘umami’ taste of the sea into your vegan dinners, without harming any sea creatures in the process.

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Written by

Rosie Martin

Rosie is a plant-based registered dietitian working in the NHS as Employee Health & Wellness Dietitian for NHS staff. As a former zoologist working in animal welfare, Rosie turned to a vegan diet in 2014. Having studied and experienced the physical and psychological benefits of a diet based on whole plant food, Rosie now works to support others embrace a plant-based diet for human, planetary and animal health through her business, Rosemary Nutrition & Dietetics. Rosie is also a board member of Plant Based Health Professionals UK.

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