Limu moui is a brown seaweed from the South Pacific, and it is the ingredient LIMU Original was built around. We sell that drink, so this is not a neutral account, but the facts below are ones you can check.
One clarification before anything else, because our own marketing has blurred it: Tonga is where limu moui grows and where this product came from, and the current blend is not drawn from Tongan waters alone. The sourcing was diversified before the brand changed hands, which we set out in what happened to LIMU.
An old food, in a specific place
Limu moui grows in the waters around the Kingdom of Tonga, in the South Pacific. It is usually identified as Sphaerotrichia divaricata. It grows in broad underwater fields, closer in character to a kelp bed than to the stringy weed you step over on a beach.
People in Tonga have eaten it for something on the order of a thousand years, both as food and as a traditional remedy. That is a long safety record of the informal kind, and it is worth exactly what informal safety records are worth: useful context, not evidence of a specific effect.
What is in it
Seaweed is nutritionally dense in a way that surprises people used to thinking of vegetables as land plants. Limu moui contains vitamins, minerals, amino acids, fatty acids, sterols and a group of complex carbohydrates that includes the one it is best known for.
The genuinely interesting part is not any single nutrient. It is that seaweed takes up trace minerals directly from seawater, which is itself a fairly complete mineral solution. A land plant can only offer what is in the soil it grew in, and a great deal of farmland has been growing the same crops for a long time.
How it is harvested
The growth rate is the thing that makes this sustainable rather than merely marketed as sustainable. In good conditions limu moui adds up to two feet a day, on nothing but sunlight and seawater.
Harvesting is done by trimming. Roughly three quarters of the plant is taken and a quarter is left anchored to the sea floor, so the plant regrows rather than being removed. The Tongan government regulates the practice, which is the part that matters: a harvesting rule nobody enforces is a marketing line.
The compound it is known for
Brown seaweeds contain fucoidan, a sulfated polysaccharide, and limu moui is one of the species used commercially to obtain it.
There is a large research literature on fucoidan. You can see it yourself on PubMed rather than take our summary of it, and we would rather you did. The short version is that the volume of work is real and unusual, and that the great majority of it is laboratory and animal research rather than trials in people. We go through what that means in our full guide to fucoidan.
What we are not going to do is list what those studies looked at. On a page selling seaweed, a list of paper titles is an argument dressed as a bibliography, and this article used to end with one.
The honest problem with seaweed
Most people outside coastal Asia and the Pacific have no habit of eating it and do not much like the taste. That is the actual barrier, and it is why seaweed mostly reaches Western diets as a supplement, a powder or a drink rather than as a vegetable.
It is also a fair reason to be sceptical of anyone selling you a seaweed product: the reason it is a supplement is partly nutritional and partly that the food itself is a hard sell.
If you want the wider picture, we wrote Seaweed 101 on what is and is not established about seaweed generally.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
More on this subject: Fucoidan & Seaweed