Ascophyllum nodosum

BotanicalSeaweed

What is it

Ascophyllum nodosum (Atlantic kelp, knotted wrack) is a brown seaweed harvested primarily from the North Atlantic. It is rich in iodine, alginate (soluble fiber), fucoidan, and polyphenols. Used in supplements for iodine support, weight management, and as a source of trace minerals.

Evidence for 2 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Iodine source

Strong Evidence

Natural source of iodine.

Postprandial glycemic control

Limited Evidence

Small studies of A. nodosum extracts show modest reductions in post-meal blood glucose.

How it works

Like other brown seaweeds, A. nodosum provides iodine for thyroid function. Its high alginate content forms a viscous gel in the stomach that may slow gastric emptying, modestly reduce post-meal blood glucose, and enhance satiety. Some weight management studies of A. nodosum extracts (combined with grape seed extract in the InSea2 formulation) have shown modest reductions in carbohydrate absorption.

Dosage

Variable. Iodine content per serving can range widely. Standardized extracts (e.g., InSea2) are dosed at 500 mg/day in clinical trials.

When and how to take it

Per product instructions. For glycemic effects, taken before meals.

1 commercial form

Compare the main delivery options and what they’re best suited for.

A. nodosum extract

Used in weight management formulations.

Standardized for polyphenol or alginate content.

Safety

Same iodine cautions as other kelps. Alginate may modestly reduce mineral absorption when taken with meals. Heavy metal accumulation concerns - choose tested sources.

Who should be cautious

Same as kelp - caution in thyroid autoimmune disease, pregnancy, and iodine excess.

Interactions

Iodine interactions (thyroid medications, lithium). Alginate may bind minerals.

Frequently asked questions

Is Ascophyllum nodosum the same as kelp?⌄

It is one species of kelp. Different kelp species have different iodine and bioactive content.

References

Ascophyllum nodosum on Wikidata — Wikidata link

Ascophyllum nodosum on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Ascophyllum nodosum (PubMed search) — PubMed link

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.