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The green sludge that could transform our diets


Microalgae is rich in protein, amino acids, fatty acids, and vitamins. Should we all be eating it?

More than 820 million people in the world do not have enough food to eat, and since 2015 the number of undernourished people in the world has been rising for the first time in decades. Now, in the midst of the coronavirus pandemic, the way we grow and supply food is under even more pressure. Producers and global supply chains face a unique challenge to adapt to the crisis and still put meals on billions of tables. At the same time, the way we produce food is having a huge impact on the planet.

“Our global food system fails on its most profound premise to provide humanity with healthy and food-secure lives,” says Asaf Tzachor, who leads research on global food security and emerging technologies at the Centre for the Study of Existential Risk at the University of Cambridge.

The vulnerability of our food supplies has been thrown into focus in recent months due to the restrictions put in place to control the spread of the virus and rapid fluctuations in demand due to stockpiling. UN health and food officials have warned that the shocks these are likely to bring to the food system could potentially disrupt supplies. Faced with difficulties in importing produce, many countries are looking for alternative ways to bolster their supplies.

To fight global hunger and increase food security, the demand for crops like soybean – widely used as animal feed – is expected to increase 80% by 2050. But producing soy requires large amounts of water and is driving deforestation in South America, leading to more environmental damage. “Alternative food sources and alternative food systems are, therefore, essential to develop and deploy, at scale, if global food security is ever to be realised,” says Tzachor.

One potential alternative food source – both for humans and the animals we eat – is algae. Could the green stuff that appears on ponds and lakes after a particularly warm spell be the answer to the planet’s food security problems?

Humans have eaten macroalgae, like wakame and nori seaweed, for thousands of years. But recently attention has turned to the nutritional and environmental potential of their microscopic cousins.

A rope covered in wakame seaweed

Edible seaweed like wakama is a type of macroalgae. (Credit: Getty Images)

Microalgae are tiny protein-rich organisms found in both fresh and seawater. They typically contain essential amino acids, essential fatty acids, including omega-3, omega-6 along with omega-7, along with vitamins, such as A, D and E. The nutritional content varies depending on the type of microalgae, but two currently dominate the market for human consumption. The first is a group of species (known as a “genus”) called Chlorella. The second is the genus Arthrospira, more commonly known as “Spirulina”. Both are rich in nutrients.

Last year, Tzachor visited a small-scale microalgae farm in Iceland run by Israel-based company Algaennovation. The farm uses geothermal electricity to power LEDs that light transparent tubes called photobioreactors.

It’s clear we’ve got to diversify our food sources – Alison Smith

Inside the photobioreactors, waste water and carbon dioxide from electricity generation, along with the LED light, fuel the growth of the microalgae Chlorella and Nannochloropsis, along with a cyanobacterium – a type of bacteria that can photosynthesise – of the genus Arthrospira. This cyanobacterium is often referred to as “spirulina” although, confusingly, Spirulina is also a genus of cyanobacteria in its own right (and so gets the capital letter).

Though cyanobacteria like Arthrospira are not algae, they are often grouped in together because they grow on water, photosynthesise and can provide many of the same nutrients.

“From an ecological footprint perspective, cultivating microalgae in the Icelandic facility is extremely efficient, as opposed to other algae cultivation methods,” Tzachor says. The process removes carbon from the atmosphere so is net carbon negative, according to Algaennation. On top of this, there are no herbicides or pesticides needed, and no waste produced to contaminate the environment.

Photobioreactors filled with growing microalgae

Microalgae grow inside photobioreactors, feeding off carbon dioxide and light (Credit: Getty Images)

The site, which started out as a trial, has been fully operational since July 2019. Instead of being cultivated for human food, the algae grown at Algaennovation is fed to fish in aquaculture, replacing unsustainable fishmeal – wild fish caught in the millions of tonnes every year in order to feed farmed fish. Algae make a great alternative because they are rich in omega-3, which fish can’t produce themselves, and so need to get it from their diet.

Tzachor says while the system is based on geothermal energy currently, it could also work using hydroelectric power plants, meaning it could be replicated in many other parts of the world.

The photobioreactors in Iceland are not the only way to cultivate microalgae – and other methods come with environmental benefits, too.

In New Mexico, US, Green Stream Farms is growing microalgae in open ponds of brackish water – slightly salty water that typically can’t be used to grow crops – using sunlight for energy. In Scotland, a company called MiAlgae hopes to produce algae using waste-water from whisky distilleries, which it claims is nutrient-rich and perfect for cultivating microalgae. In January this year, MiAlgae received £1m ($1.28m) in funding that will be used to grow its business and move towards commercialisation by building a demonstrator plant.

While microalgae consumption is not yet widespread, the case for algae becoming a source of food in our future is strong. With demand for soybean increasing, and the land and water uses of agriculture simply unsustainable, humans need an alternative protein source. “It’s clear we’ve got to diversify our food sources,” says Alison Smith, professor of plant sciences at the University of Cambridge.

A field of soybean plants

Microalgae takes up less growing space than soybeans (Credit: Getty Images)

So how does algae shape up as a protein source? According to Smith, fresh algae shouldn’t be considered a direct replacement for soybean, currently a large source of protein for both humans and the animals humans eat. In fresh microalgae, the average proportion of protein is the same as a spinach leaf, which is around 3% of its weight.

But in dried microalgae such as spirulina protein per weight varies from 30% to 60%, making it comparable to soybean, which is about 35% to 40% protein. Plus, algae can provide more of the essential amino acids than soybean provides.

It also has the potential to reduce the amount of land we use to grow protein. A paper published last year says microalgae produces 4-15 tonnes of protein per hectare per year, compared to 0.6-1.2 for soybean.

There are some other obstacles to overcome, too. And at the moment, says Smith, we don’t know if eating algae would be as good for us as something like spinach. That’s because there is not enough research looking into whether the nutrients in algae are bio-accessible, meaning they can be released from the food in our intestines, or bio-available, meaning they will be absorbed by our bodies.

Plus, she says, it remains to be seen if we can really grow algae for food on a scale that genuinely could feed the world. While productivity might have been demonstrated on small scales, making it commercially is a totally different thing.

Still, Smith is certain algae will play a role in the food of our future, even if only as a supplement: “Algae offer a source of vitamins you can’t get from soybean, and actually there’s one vitamin you can’t get from spinach either.”

A wooden spoon in scooping from a pile of spirulina

Some types of microalgae are already sold as food supplements (Credit: Getty Images)

That vitamin is B12, which is often missing from plant-based diets because it is mostly found in meat, fish, dairy and eggs. The algae themselves don’t make B12, but they absorb it from their environment. “They live in a liquid culture, and there’s lots of bacteria there as well,” she says. These bacteria are the ones producing the vitamin B12, which is then taken up by the algae. If humans switch to more plant-based diets, algae could be a vital source of B12.

In fact, there are already algae-based food supplements on the market. Products like Chlorella, which are whole algae, are added to certain drinks, but mostly they are sold in a powder form as dietary supplements.

But it’s the environmental benefits of replacing or supplementing traditional foods with microalgae that might make the biggest difference to our lives.

Contemporary food systems exhaust the biosphere by eroding soils and contaminating groundwater, leading to the logging of forests and the fragmentation of habitats, says Tzachor while being sensitive to a range of risks like bad weather, pests and pathogens.

“On all of these accounts, microalgae are not a good source of food for the future,” says Tzachor. “Rather, if cultivated properly, they are an ideal source.”

Images: Getty Images

This article is part of Follow the Food , a series investigating how agriculture is responding to environmental challenges. Follow the Food traces emerging answers to these problems – both high-tech and low-tech, local and global – from farmers, growers and researchers across six continents.