The more seaweed we eat, the healthier the sea gets

Seaweed absorbs excess seawater nutrients and is a super healthy vegetable

16-Feb-2022 - Denmark

When you think of seaweed, you may conjure up images of smelly, brown accumulations on the beach or unpleasant tickling sensations on your belly skin during a swim. But these are far from the images that Susan Løvstad Holdt sees in her mind’s eye.


“Seaweed contains lots of interesting substances. It’s a fantastic resource, and we need more of it,” says Susan with great enthusiasm.

Susan Løvstad Holdt is Associate Professor at DTU Food and has worked with seaweed since 2003. I catch up with her at one of the Danes’ favourite summer events, a festival—in this case a seaweed festival—which unfolds over three days in July in the beautiful Anneberg Culture Park in Nykøbing Sjælland. Here, Susan disseminates her knowledge about seaweed together with Danish food producers, restaurants, artists, and other seaweed enthusiasts.

Vegetable of the sea

Less than ten years ago, hardly any Danes knew that you could eat seaweed. It could—at a pinch—be used to bind the rice together in a maki roll ordered in a sushi restaurant. And environment, sustainability, and climate were not issues associated with seaweed.

The situation is completely different now, and if it were up to Susan—in less than ten years from now—we will all have seaweed as a completely natural food in our kitchen in line with carrots and tomatoes. But why should we incorporate seaweed in our daily household? According to Susan, there are many good reasons for this, not least from a sustainability perspective:

“We don’t need to fertilize the seaweed because it absorbs some of the nutritive salts that water environment plans would like to reduce in the sea. We don’t use fresh water during the cultivation, and we don’t use any land for the cultivation.”

And seaweed is super healthy with its contents of vitamins, minerals, and antioxidants—to name but a few of the nutrients contained in seaweed.

“Seaweed is the vegetable of the sea,” states Susan Løvstad Holdt.

Danish Knowledge Centre for Seaweed

DTU Food Institute participates in the dissemination collaboration known as Danish Knowledge Centre for Seaweed. Here, researchers from DTU and the University of Copenhagen are engaged in a collaboration with the firm Danish Seaweed, the interest organisation National Centre for Local Foods, Geopark Odsherred, and Anneberg Culture Park.

The purpose of the knowledge centre is to collect and disseminate knowledge about seaweed and to create a network for researchers and entrepreneurs with focus on seaweed as a raw material. The overall goal is to create a basis for sustainable seaweed production in Denmark. And the goal for Susan Løvstad Holdt’s involvement in the knowledge centre is clear:

“Having your finger on the pulse and being in touch with what is happening in the industry. What do they want to know, what are the challenges they face, where do they see an opportunity for their business, and then create some partnerships in which we—as a university—can help solve these problems.”

“This has formed part of our work in a number of projects with Danish Seaweed. They would like to cultivate some types of seaweed on ropes, but they also want to know how healthy the seaweed is after they’ve made a mild form of drying of their products.”

Danish Seaweed

Danish Seaweed is a small Danish entrepreneurial firm, which was set up in 2016. Simon Weber Marcussen is a co-founder and partner, and he sees some clear advantages of their collaboration with DTU Food:

"We don’t need to plough, irrigate, fertilize, or spray with pesticides. We don’t impact nature in any other way than by putting out a rope on which the seaweed can grow."Simon Weber Marcussen, partner in the firm Danish Seaweed

“As an entrepreneur, it’s important to have a lifeline in the form of researchers. DTU Food has helped us every time there have been some barriers that we haven’t been able to break down ourselves.”

This may, for example, be questions about how the contents of protein or bioactive substances change over the year, and what types of seaweed can be grown in southern Danish waters, where the salt content is lower than what most seaweed species appreciate.

“These are the types of questions of doubt that a first mover will encounter, and where it’s good to have some researchers to use as sounding boards. And DTU Food is brilliant at that.”

Danish Seaweed harvests around ten tonnes of seaweed annually, and the seaweed is sold both fresh to restaurants and canteens and as dried seaweed, primarily through health food stores.

Sales of fresh seaweed really took off when the Michelin restaurant Noma contacted the firm in 2018. Once Noma put seaweed on the menu, all self-respecting Danish restaurants wanted seaweed, and Danish Seaweed now delivers about 200 kg of fresh seaweed to restaurants and canteens—every month, all year round.

Healthy and sustainable

Both Simon and Susan believe that seaweed has much more to offer in the future than merely as a trendy phenomenon in Danish restaurants. Seaweed has some completely unique flavour nuances, and it contains a number of attractive substances.

“Seaweed contains many natural antioxidants, and they may be healthy alternatives to some of the synthetic antioxidants we’re currently using,” explains Susan Løvstad Holdt.

Seaweed is also rich in protein—certain types can easily match the content of soybeans. Seaweed is also rich in vitamins A, B, C, and E, and it has a high content of iron, calcium, phosphorus, and magnesium. Seaweed also contains the healthy polyunsaturated omega-3 and omega-6 fatty acids, and the ratio of these two fatty acids is close to being optimal in relation to healthy foods.

Another good property of seaweed is that it absorbs some of the nutrients that are added in excessive quantities to our marine environment in connection with conventional agriculture. Sugar seaweed—one of the seaweed species in Denmark with the greatest cultivation potential—absorbs around 25 kg nitrogen and 2 kg phosphorus per hectare of cultivated area. So when you harvest the seaweed, you simply remove the excess nutrients from the seawater, thus improving the aquatic environment.

Both cultivated seaweed and harvested natural seaweed entail a production that is much more environmentally and climate friendly than conventional agriculture.

“We don’t need to plough, irrigate, fertilize, or spray with pesticides. We don’t impact nature in any other way than by putting out a rope on which the seaweed can grow. The seaweed takes care of itself. We put out the ropes by boat once a year and collect them again once a year, which requires around 15 litres of petrol. So this process is almost carbon neutral,” says Simon Weber Marcussen.

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