Seaweed is one of nature’s most nutrient-rich and sustainable superfoods - and it’s rapidly earning its place in modern wellness routines. Naturally rich in the key nutrient iodine, seaweed supports thyroid health, sustained energy levels, hormonal balance, and cognitive function. Simple to incorporate into daily life, seaweed supplements offer an easy, effective way to support your health from within.
At Doctor Seaweed, we’ve spent years researching the benefits of Scottish seaweed and how different species vary nutritionally. One question we’re asked time and time again is: what’s the difference between seaweed and kelp?
The terms are often used interchangeably, but they’re not actually the same thing. Understanding the difference can help you make more informed choices when choosing seaweed supplements or iodine supplements.
What is seaweed?
Seaweed is a broad term used to describe thousands of species of marine algae that grow in oceans, lochs and coastal waters around the world. In fact, there are over 10,000 known species of seaweed, grouped into three main colour categories:
- Brown seaweed
- Red seaweed
- Green seaweed
Seaweed absorbs nutrients from seawater and uses sunlight to grow, making it naturally rich in key minerals, compounds, and antioxidants.
At Doctor Seaweed, we use specialise in a species called Ascophyllum nodosum - a brown seaweed traditionally known as knotted wrack or egg wrack. We sustainably harvest our organic Scottish seaweed from the pristine waters of the Outer Hebrides, where the clean environment and strong tidal conditions help create a nutrient-rich seaweed naturally high in iodine.
Our seaweed grows in the intertidal zone, meaning it is exposed to changing conditions between low and high tide every single day. Researchers believe these environmental stresses may contribute to the unique nutritional profile and antioxidant content found in this species.
You may also hear seaweed referred to as:
- Marine macroalgae
- Sea vegetables
- Ocean plants
These are simply different terms describing edible seaweed species used in food, wellness and supplements.
So, what is kelp?
Kelp is actually a type of seaweed - specifically, a subgroup of large brown seaweeds.
While all kelp is seaweed, not all seaweed is kelp.
Kelp species are generally much larger than other seaweeds and are typically found growing in nutrient-rich saltwater along rocky coastlines. Some species form huge underwater kelp forests that provide habitats for marine wildlife.
Popular kelp varieties include:
- Kombu
- Bull kelp
- Bladderwrack
- Laminaria species
One important thing to understand is that the term “kelp” is used differently around the world. In some countries, particularly North America, “kelp” is sometimes used to describe almost all brown seaweeds - even though scientifically that isn’t always accurate.
This is why checking the actual species name matters when choosing a seaweed supplement.
Seaweed vs kelp: the nutritional difference
Different species of seaweed can vary hugely in their nutritional content, particularly when it comes to iodine.
Brown seaweeds (including kelp) naturally contain higher iodine levels than red or green seaweeds. However, some kelp species can contain extremely high and inconsistent iodine concentrations, depending on where and how they are harvested.
That’s why sourcing and testing are so important.
At Doctor Seaweed, every batch of our organic Scottish seaweed is independently tested for iodine levels to ensure consistency, traceability and safety. Our supplements contain only 100% pure Hebridean Ascophyllum nodosum seaweed with no unnecessary fillers or binders.
When comparing seaweed supplements or iodine supplements, it’s important to look for:
- Clearly identified seaweed species
- Sustainable sourcing
- Traceable harvesting
- Batch testing for iodine levels
- Minimal ingredients
Why is iodine important?
Iodine is an essential mineral that supports:
- Healthy thyroid function
- Cognitive function
- Balanced metabolism
- Hair, skin & nail health
- Growth in children
Despite its vital role in overall health, iodine deficiency remains surprisingly common in the west - particularly among those who consume little seafood or dairy. Research suggests that up to 84% of women in the UK may not be getting enough iodine, while recent findings published in The Lancet highlighted that an estimated 5 billion people worldwide are iodine deficient. If this were vitamin D or calcium, it would be making headlines. Could you be deficient in essential iodine? Click here to take our 20 second quiz to find out.
This is one reason why seaweed supplements have become increasingly popular as a natural iodine source.
Our organic seaweed supplements provide a convenient way to support your daily iodine intake using sustainably harvested Scottish seaweed.
Dr Craig Rose PhD is a marine biologist and founder of Doctor Seaweed. His lifelong interest in seaweed and marine ecosystems inspired the creation of the brand. Pictured below on a dive trip, Craig is in his element exploring the underwater.
Why we use Scottish seaweed
Not all seaweed is created equal.
At Doctor Seaweed, we harvest our seaweed from the clean, mineral-rich waters surrounding the Scottish Outer Hebrides. Sustainability and traceability are central to everything we do, from harvesting to production.
Our seaweed is:
- Sustainably harvested
- Fully traceable
- Carefully tested for iodine content
- Naturally rich in minerals
- Suitable for vegan and plant-based diets
Because our supplements contain only pure seaweed, they offer a simple and natural alternative to synthetic iodine supplements.
What about spirulina - is that seaweed too?
Not quite.
Although spirulina is often grouped alongside seaweed supplements, it’s actually a type of cyanobacteria commonly referred to as blue-green algae.
Unlike seaweed:
- Spirulina grows in freshwater
- It is a microalgae, not a macroalgae
- It is not a brown seaweed or kelp species
Because of the similar “superfood” reputation, spirulina and seaweed are often confused - but they are very different organisms with different nutritional profiles. The same applies to sea moss - this is an extract rather than a seaweed food source.
