How and why to eat seaweed: nutritional benefitspitfallshow to usesources

What exactly is seaweed?

Seaweed is an informal term for multi-celled algal organisms that grow in salt water. Whereas single-celled organisms such as chlorella are known as microalgae, seaweed is known as macroalgae. It’s generally grouped by colour:

  • Brown: kelp (e.g. arame, kombu, wakame), fucales (e.g. bladderwrack, hijiki, sea spaghetti)
  • Red: dulse, laver (a.k.a. nori), Irish moss
  • Green: sea lettuce, sea greens

Seaweed can be found along most of the coastline of the British Isles. It grows quickly, making it very sustainable, and it can take up nutrients over its entire surface. Whereas some types of kelp in the Pacific can grow up to 50 metres tall, the UK equivalent reaches about 3 metres (1).

Edible seaweed is usually associated with Asian countries, especially Japan, where it’s been eaten for 6,000 years. But it was actually part of the UK and Irish diets for at least 4,000 years, commonly eaten in coastal regions until the early 20th century. (2)

Nowadays it’s seeing a revival in the West, not only as a wrapping for sushi in every high-street supermarket, but also prized for its savoury umame flavour in cooking.

seaweed on coast

Nutritional values of seaweed

Seaweed is very good at absorbing nutrients from its habitat. It can potentially provide the full spectrum of minerals the body needs – in higher concentrations than are found in vegetables. It’s especially high in iodine and potassium, as well as having good levels of calcium, iron and magnesium.

It contains good quality protein, covering a spectrum of amino acids, is high in fibre, and contains omega oils. However, the levels of these nutrients will be pretty low in a standard serving size.

Many claim seaweed is a good source of B vitamins. This is tricky, as levels can easily be reduced or destroyed in processing. B6, for example, is sensitive to air and UV light. Cooking can also further reduce B vitamins.

Nutritional values of seaweed should be taken with a big pinch of sea salt 🙂 Due to environmental factors such as location, freshness, time of year, the way it’s dried and stored, there will be significant variations. The following figures are just provided for interest.

Seaweed – nutritional values

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Further health benefits of seaweed

1. Gut bacteria

Seaweed is emerging as a significant prebiotic (4). It contains certain types of fibre and carbohydrate that the human body can’t digest, but which our gut bacteria can feed on, thus strengthening our digestive health and general wellbeing.

2. Toxins

In the same way as seaweed is good at absorbing nutrients, it’s also good at absorbing toxins. This can be a good thing when ingested, as it can help soak up heavy metals such as lead and cadmium that we absorb from the environment (see Pitfall #2 below).

3. Heart health

Research has shown seaweed to be beneficial in lowering blood pressure and improving heart health (5).

4. Cancer

Nutrients known as fucoidans, found in brown seaweeds, can help fight cancer (6). Seaweed also contains lignans, which may help specifically against hormonal cancers (7).

5. Neurological disease & arthritis

Fucoidans also have anti-inflammatory properties, helpful in treating neurological disorders such as Alzheimer’s and Parkinson’s (8), as well as arthritis (9).

5. Diabetes

Seaweed can be beneficial in regulating blood glucose levels, so may be helpful against diabetes (10).

6. Thyroid function

Iodine deficiency is on the rise worldwide, leading to underactive thyroid problems, as well as a range of developmental problems in children (11). Contaminants such as perchlorate – found in water and food supplies – can block the absorption of this important mineral (12).

Those eating the average UK diet probably get enough iodine (13) – for example most table salt is fortified with it – but on a health-conscious diet it’s actually a little more complicated.

  • If you’re on a low-sodium diet, you won’t be getting much iodine from salt. If you’re using sea salt or Himalaya salt instead of regular table salt, it will only have naturally occurring iodine, present only in small amounts.
  • Research shows that vegans are especially likely to be deficient (14). Iodine is naturally present in fish – originally from the algae they eat – and it’s also used in milk production. Vegans obviously will not benefit from either of these sources. It’s possible to get iodine from fresh vegetables, but the amount largely depends on the quality of the soil they’re grown in.
  • The added complication is that iodine levels can be further reduced by goitrogens, present in raw brassicas such as broccoli, cabbage and kale, as well as soy and flax – all common in a plant-based diet. While cooking reduces goitrogens, it also reduces iodine levels, so if you’re looking to seaweed as a source of iodine, it needs to be eaten raw (see Pitfall #1 below).


Pitfalls of seaweed

While it has many health benefits, seaweed is a powerful ingredient, to be used with care. Please seek advice from a health practitioner if you have an existing medical condition. Even if your health is good, it’s best to start with a small amount of cooked seaweed a couple of times a week, before increasing servings or incorporating it raw.

1. Thyroid function (again)

Too much iodine can have a negative effect on thyroid function. Not only can it lead to the thyroid becoming over-active, but also, strangely, could actually make an under-active thyroid worse in some cases (15).

2. Toxins (again)

As mentioned above, seaweed can be a great detoxifier, binding to heavy metals and other toxins in the body. By the same token, it may already have absorbed toxins and even radioactive material from the sea before it’s harvested. It’s therefore very important to use reliable sources.

3. Kidney function

Those with kidney disorders may have trouble regulating potassium in the blood. As seaweed is high in potassium, it’s probably best avoided.

4. Arsenic

Seaweed can contain small amounts of naturally-occurring arsenic, but in most types it’s negligible. The only type that might contain significant amounts is thought to be hijiki (16). Some may say that if the amount was significant, there would be wide-spread arsenic poisoning in countries like Japan and Korea 🙂 But actually it could be that if you’re brought up eating it, your body learns to cope with it. Research has shown that some have more of an adverse reaction to it than others (17).

5. Sodium

Due to its salty habitat, seaweed is naturally high in sodium, so take care if you need to limit your intake. Many commercial snacks, such as individual packs of nori, also have salt added.

cornwall ocean

How to use seaweed

  • It’s probably most familiar as toasted laver (nori) – the wrapping for sushi rolls. Nori is also widely available in snack form.
  • Dried dulse can be eaten as a snack on its own, but it’s rather an acquired taste – some liken it to bacon.
  • Adding dried flakes to soups, curries or stews in cooking gives a lovely savoury boost, and enriches the flavour of other ingredients. Earthy types like kombu and dulse are especially good for this use.
  • Dried flakes can also be sprinkled on salads or added to your smoothie mix. You may want to go for lighter types in this case, such as sea greens.
  • Some types can be used as gluten-free, low-carb alternatives to pasta – e.g. sea spaghetti, or kelp sheets in lasagne.
  • If you’re brave, you can just rehydrate dried seaweed and eat it as a salad, but the texture can be quite challenging if you’re not used to it. Again, lighter types are best for this use. To make it more palatable, try adding savoury flavours such as spring onion, tamari, miso and toasted sesame.
  • Adding a strip of kombu to the water when boiling beans and pulses helps to reduce digestive problems such as gas and bloating.
  • In South Wales, laver bread – a mixture of laver and oats – is traditionally served with breakfast.
  • You could add dried flakes to bread dough before baking.
  • Agar agar is a great gelatin substitute in cooking and baking.
  • Irish moss can be used as a thickener for soups and sauces.
  • If you want the benefits of seaweed, but really can’t handle the flavour or texture, kelp extract can also be bought in supplement form.
  • If you’re growing your own organic vegetables, liquid seaweed is a great fertiliser. It’s rich in potassium, magnesium and trace elements. These not only help the plant grow, but also boost its nutritional value. We use Vitax Organic Liquid Seaweed.

Where to get seaweed

We love The Cornish Seaweed Company. All their products are certified organic and sustainably sourced.

If you live near a pure enough stretch of sea, you could have a go at foraging for your own, and eating it fresh. You’ll find some tips on UK varieties at

Got any tips or questions of your own about eating seaweed? Leave us a comment below, we’d love to hear from you.


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