Seaweed Nutraceuticals and Functional Foods: Fucoidan, Fucoxanthin, Phlorotannins and Alginate

By Jayson Byles, forager & chef · September 2026 · reviewed September 2026

Seaweed nutraceuticals are food ingredients and supplements made from seaweed compounds that are sold for a health purpose rather than for flavour: fucoidan and fucoxanthin from the brown seaweeds, phlorotannins from the wracks, alginate and laminarin from the kelps, and whole-seaweed powders valued for iodine and fibre. This is a plain guide for the people who make them: what is in which Scottish species, where the human evidence really stands, what the law lets you say, and how to get clean, identified raw material. It is one of the other uses of seaweed we cut for on the Fife shore, and the one where the gap between laboratory promise and proof is widest.

What is in seaweed, and which species carries it

Seaweeds are not plants, and their chemistry is their own. Five families of compounds account for most of the nutraceutical interest.

• Fucoidan. A sulphated polysaccharide found only in brown seaweeds. On our shore that means the wracks (Fucus vesiculosus, Fucus serratus), sugar kelp (Saccharina latissima), oarweed (Laminaria digitata), dabberlocks (Alaria esculenta) and sea spaghetti (Himanthalia elongata). It is the compound behind most seaweed supplements.
• Fucoxanthin. The pigment that makes brown seaweed brown. Studied for body-weight and metabolic effects, with one or two small human trials and a great deal of animal work.
• Phlorotannins. The polyphenols that make the wracks taste the way they do. Antioxidant in the test tube, studied for glucose metabolism, and the richest source we cut is bladderwrack.
• Alginate and laminarin. The structural and storage polysaccharides of the kelps. Alginate is a soluble fibre that forms a gel in the stomach, which is why it has been studied for satiety and fat absorption; laminarin is studied as a prebiotic.
• Whole-seaweed nutrition. Dulse (Palmaria palmata) carries useful protein, iron, calcium and iodine with vitamins A to D. Every seaweed carries iodine, the kelps in very large amounts, and iodine is the one seaweed nutrient with authorised health claims attached.

What the human evidence shows

The honest summary is that the polysaccharides are well characterised, the animal work is extensive, and the human trials are small. That is not a reason to walk away; it is the reason to read the trials rather than the marketing.

Fucoidan. A 2022 systematic review of fucoidan alongside cancer treatment found four usable studies and no consensus. Since then the trials have got a little bigger and a little better. A 2025 randomised trial in Scientific Reports gave fucoidan to adults doing six weeks of resistance training and reported improved anaerobic performance and body composition against placebo; it is one trial, over six weeks, in trained volunteers. A UK remote study of a fucoidan supplement for gut health ran from September 2024 to August 2025 and is yet to report in full. The Mayo Clinic trial of fucoidan against chemotherapy-related fatigue is due to complete in 2027, and is the kind of study the field has lacked.

Fucoxanthin. The human record is mixed. One trial combining fucoxanthin with pomegranate-seed oil reported around 4.9 kg of weight loss over sixteen weeks; another, at 1 to 2 mg a day in Japanese adults, found no effect (reviewed here). A 2022 systematic review counted a single clinical trial in five years.

Alginate. The most British story in the field. Newcastle University showed in 2010 that alginate cut fat digestion by up to 75 per cent in a model gut, and in 2014 the bakery chain Greggs baked a bread with 4 per cent alginate for a human trial (Newcastle University). The effect is real as a soluble fibre; the size of the effect at a dose people will eat is the open question.

Phlorotannins. A Phase I safety trial of an Ecklonia cava phlorotannin extract has been registered, which tells you where the evidence sits: safety first, efficacy later. A 2024 review in Foods sets out Fucus vesiculosus extracts as functional-food ingredients, with the same caveat.

The iodine question

Iodine is the reason seaweed gets both praise and warnings. Adults need about 140 micrograms a day, according to the NHS, which also says that taking 0.5 mg or less a day of iodine supplements is unlikely to cause any harm. Brown seaweeds can hold thousands of milligrams per kilogram of dry weight. A 2023 University of Glasgow survey of UK seaweed foods found the range of products had more than doubled since 2015 and that the median single serving carried more than 400 micrograms of iodine, with some supplements above the tolerable upper level. The Committee on Toxicity advises particular caution with kelp and kombu around pregnancy and for infants. If you are formulating, the iodine content of your raw material is the first number to measure.

What you are allowed to say

The Great Britain Nutrition and Health Claims Register is the only list that matters. Iodine has authorised claims: it contributes to normal thyroid function, the normal production of thyroid hormones, normal cognitive function, normal energy-yielding metabolism, normal skin and the normal functioning of the nervous system, and they can only be used where a portion supplies at least 15 per cent of the reference intake. There are no authorised health claims for fucoidan, fucoxanthin, phlorotannins or laminarin at all, and none for weight loss, detoxing or treating thyroid conditions. Products that make them are advertising unlawfully under the CAP Code, and a claim that a food treats a disease can make it a medicine by presentation in the eyes of the MHRA.

Novel-food status is the other gate. Whole seaweeds with a history of consumption in Europe before 1997 are not novel: dulse, bladderwrack, oarweed, sugar kelp, sea lettuce, carrageen, sea spaghetti and dabberlocks are all on the list. An extract or isolate usually is novel and needs authorisation before sale. Fucoidan extracts from Undaria pinnatifida and Fucus vesiculosus are authorised in Great Britain at up to 250 mg a day; a fucoidan from another species, or a higher dose, would need its own application. The Food Standards Agency’s guidance covers the process.

Scotland’s place in this

The Scottish Government’s 2022 study of the sector put it at roughly £4 million of turnover and 59 jobs, small but growing, with bioactives modelled as the fastest-growing segment at 7 to 10 per cent a year. In January 2024 Oceanium in Oban launched a fucoidan ingredient at more than 75 per cent purity and a kelp fibre, made from farmed European kelp after a 79-tonne biorefinery run: proof that the extraction end of the chain now exists in Scotland. The Hebridean Seaweed Company supplies technical ingredients from Lewis, and the University of Glasgow’s human nutrition group is the UK authority on seaweed iodine. Scotland’s case against France and Portugal is clean water, cool seas and identity: a named species from a named shore, cut on a known date.

Wild harvesting is licensed. Anything beyond personal use on Crown foreshore or seabed needs a licence from Crown Estate Scotland, granted once NatureScot confirms no unacceptable environmental risk. We harvest under those rules; our plain guide to the law explains how the line between the pot and the trade works, and the history of seaweed in Scotland explains how a Fife shore came to be in this business in the first place.

What to ask a supplier

Whether you buy from us or anyone else, these are the questions that separate raw material you can build on from a bag of weed.

• Species, with the Latin name, and whether the batch is single-species.
• Which shore, and the date it was cut. Water quality follows from the first; freshness from the second.
• How it was harvested. Cut above the growing point on a rotation, or pulled. It matters for the bed and it matters for consistency next year; we cut, never pull.
• How it was handled: rinsed in clean seawater, chilled within hours, dried low and slow or hot and fast. Heat changes the chemistry, and fucoidan and phlorotannin content both move with the season.
• Whether batch testing is available: iodine, heavy metals, microbiology, and a certificate of analysis for the lot you receive.
• Whether what you intend to make is a novel food, and whether the claim you plan to make is on the register.

Getting seaweed for your project

We supply every species we harvest except laver: fresh, cut on the low tide and chilled the same day, in 5 kg lots; or dried in small bespoke batches as whole leaf, pieces or flakes. Every bag carries the species, the shore and the date. Batch testing and a certificate of analysis are available on request. We drop off by hand across the East Neuk and Fife, courier chilled across the UK, and ship dried seaweed further afield. For a first project, ask for a sample pack of what is in season and tell us what you are making; we will say what is at its best for your dates and what we would cut for it. If your interest is the pharmaceutical end, alginate dressings, raft antacids and the antiviral work, that story is on its own page: seaweed in medicine.

Sources

The figures and findings above come from these sources; the reviews are open access.

• Understanding the potential scale for seaweed-based industries in Scotland (Scottish Government, 2022)
• Licensing of wild seaweed harvesting (Crown Estate Scotland)
• Iodine (NHS)
• Great Britain nutrition and health claims register (Department of Health and Social Care)
• Food: health claims (Advertising Standards Authority)
• Guidance Note 8: a guide to what is a medicinal product (MHRA)
• Novel food authorisation: fucoidan extracts (Food Standards Agency)
• Novel foods authorisation guidance (Food Standards Agency)
• Statement on excess iodine intake around pregnancy (Committee on Toxicity, 2022)
• Seaweed products on the UK market and their iodine content (British Food Journal, 2023)
• Fucoidan supplementation with resistance training: randomised trial (Scientific Reports, 2025)
• Fucoidan supplement and gut health, UK remote study (ISRCTN, 2024)
• Fucoidan for preventing chemotherapy-related fatigue, Mayo Clinic trial (ClinicalTrials.gov)
• Effectiveness of fucoidan as supplemental therapy in cancer patients: systematic review (2022)
• Systematic review of marine algae-derived fucoxanthin (2022)
• Fucoxanthin: human trials reviewed (2017)
• Alginate bread trial (Newcastle University, 2014)
• Phase I safety trial of Ecklonia cava phlorotannins (ClinicalTrials.gov)
• Fucus vesiculosus extracts as functional food ingredients (Foods, 2024)
• Bioactives from brown algae, 2014 to 2024 (ChemBioEng Reviews, 2025)
• Oceanium biorefinery and fucoidan launch (Oceanium, 2024)
• Nutritional value and bioactive properties of dulse, knotted wrack and carrageen (Life, 2024)
• Risks and benefits of consuming edible seaweeds (Nutrition Reviews, 2019)

Questions we get asked

Which seaweed has the most fucoidan?

Fucoidan is a brown-seaweed compound. In Scottish waters the wracks (Fucus species), sugar kelp, oarweed, dabberlocks and sea spaghetti all carry it; content varies with species, season and the part of the plant, so a sample tested for your intended extraction is worth more than a general figure.

What is a seaweed nutraceutical?

A food ingredient or supplement made from a seaweed compound and sold for a health purpose rather than flavour: fucoidan and fucoxanthin from brown seaweeds, phlorotannins from the wracks, alginate fibre from the kelps, or whole-seaweed powders for iodine. In Great Britain only authorised claims may be attached to any of them.

Is fucoidan a novel food in the UK?

Extracts of fucoidan from Undaria pinnatifida and Fucus vesiculosus are authorised novel foods in Great Britain at up to 250 mg a day. Fucoidan from another species, or at a higher dose, would need its own authorisation from the Food Standards Agency before sale. Whole seaweeds with a pre-1997 history of consumption are not novel.

Can I buy raw seaweed for extraction in the UK?

Yes. We supply identified, hand-cut Scottish species fresh in 5 kg lots or dried in small bespoke batches, with the species, shore and harvest date recorded, and batch testing or a certificate of analysis available on request.

What health claims can a seaweed product make?

Only claims on the Great Britain Nutrition and Health Claims Register. Iodine has authorised claims for normal thyroid function, cognitive function, energy-yielding metabolism, skin and nervous system, where a portion supplies at least 15 per cent of the reference intake. Fucoidan, fucoxanthin and phlorotannins have no authorised claims.

This is a guide to the ingredient, not medical or regulatory advice. For claims, novel-food status and product authorisation, talk to the Food Standards Agency or a regulatory adviser before you launch.