Last year scientists tipped an aquatic weed to be the next alternative plant protein superfood.
One trial by the American Diabetes Association comparing a green duckweed shake and a yogurt-based equivalent in 20 obese participants found the duckweed to be an emerging plant protein source with potential beneficial effects on glucose levels.
So what is duckweed? As the name suggests, the plant can be found floating on water and is a food source for waterfowl, as well as tadpoles and fish. There are 37 species in the duckweed (Wolffia globosa) family. It’s particularly famous for its speedy growth rate; in optimum wind-protected waters it can double its surface area in less than two days.
While its impressive carpet-like production can choke a pond of oxygen, it has earned the accolade of the world’s fastest-growing plant. Its pint-sized fronds and blossoms make it the world’s smallest flowering plant. Water lentil is another nickname.
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Most of the hype surrounding the wonder species comes from evidence that it offers all nine essential amino acids, as well as dietary fibres, polyphenols, iron, zinc and vitamin B12. It also happens to be naturally high in vitamins A, E and B, rich in fats, and some strains exhibit particularly high protein levels.
The reality is that duckweed has more nutrition by weight than any other flowering plant. It’s often cited as a significant potential food source, particularly if the projections of food insecurity and the Earth’s population striking 10 billion come to light.
But before you ditch the pea protein and jump headfirst into your local duckpond, you should know that studies have been widely based around the commercially cultivated Mankai strain of Wolffia globosa.
After eight years of trials, Israeli plant protein company Hinoman launched the strain in 2015. The company has developed a hydroponic system that allows for the year-round growth and harvesting of Mankai. They’re calling it “the world’s smallest vegetable”.
A 2020 study found that Mankai strain of duckweed could be a potential bioavailable source of vitamin B12, while other research has shown that it may serve as an excellent alternative plant protein source compared to animal and other protein sources.
The product is sold in cube form and can be incorporated straight into home-cooked dishes, from smoothies to pasta sauces, or frozen for later use. It is said to boost nutrients without affecting the taste or smell of the food.
Planet Duckweed is another initiative looking to develop the weed on a commercial scale using a hydroponic farming platform.
In several countries throughout Southeast Asia, including Thailand, Laos and Myanmar, duckweed is already harvested for human consumption as a vegetable named ‘Khai-Nam’. It’s incorporated into salads and mixed into soups and curries. The taste has been described as mild and similar to cabbage and romaine lettuce. Some species with higher antioxidant levels are said to have a slightly bitter aftertaste.
While it is not commonly part of the Western diet, a 2019 study looking to get an impression of ideas and opinions about the nutritious pond scum found it would fit best in meals where vegetables and greens are expected.
Here in New Zealand, common duckweed (Lemna minor) is a wide-spread native used for pond cover and wastewater treatment. It also has a high protein content varying from 20 to 40 percent, and research has shown it has the potential to be a food supplement in the diet of ducks.
There’s one 2019 study looking at common duckweed in comparison with green peas. The randomised trial weighed up the amino acid, glucose and insulin levels in adults after a single intake, finding lower plasma glucose and insulin levels compared with peas.
Robert McGowan (widely known as Pa Ropata) teaches courses in traditional Māori rongoā rākau medicine. The author of A Practical Guide to Traditional Māori Medicine doesn’t know of any medicinal uses for duckweed – also known as karearea or kaarearea – but says it has a real, if not direct link to people.
“Karearea is an important food for some of the bird species that live in wetlands and lakes, as well as bringing many benefits to the waterways themselves. In the Māori way of looking at things, the main role of plants used for rongoā is to heal the whenua (the land) and all the things that belong to it.”
Nick Roskruge, Professor in Ethnobotany at Massey University, agrees saying that most Māori identify with duckweed as an algae type plant which is part of the food chain for the river life.
“It is very common in the right conditions so is a good indicator of those conditions. Its presence is often included in what most kaitiaki expect to see in their observations of the fresh water rivers and streams.”
The main concern for those seeking out wild duckweed as a nutrition smoothie addition is that it tends to grow in poor water conditions. Its ability to remove heavy metals from water like lead, copper, zinc and arsenic means that trace elements may also be present.
Professor Roskruge adds, “There has been research on the ability of some aquatic plants to take up contaminants from the water – watercress etc – so putting this into that perspective, the ‘fit for consumption’ term is not something you could state unless you were certain it didn’t take up water contaminants”.
In that case, it’s advised to only eat duckweed which has been grown and tested under controlled conditions.