Spirulina & Chlorella: The Algae Compared

When you're standing in front of the green superfood shelf, spirulina and chlorella often sit right next to each other – and yet they are two completely different organisms. The shortest difference first: spirulina is a cyanobacterium (blue-green alga) with an especially high protein content and the blue pigment phycocyanin, while chlorella is a true green alga with a firm cell wall and the highest chlorophyll content among the well-known edible algae. Anyone who combines the two brings two complementary nutrient profiles into the glass. In this guide you'll get the honest comparison – including the truth about the persistent B12 myth.

The key points at a glance

• Spirulina = cyanobacterium, roughly 55–70 % protein, rich in phycocyanin and iron.
• Chlorella = true green alga, very high chlorophyll content, firm cell wall (must be broken open).
• Neither is a reliable B12 source – they mostly supply ineffective pseudo-B12.
• Quality decides everything: origin, closed cultivation systems and laboratory testing for heavy metals.

What spirulina and chlorella actually are in the body

Botanically, the two are worlds apart. Spirulina (usually Arthrospira platensis) is, strictly speaking, not an alga at all but a spiral-shaped cyanobacterium – a photosynthesising bacterium that was already enriching the Earth's atmosphere with oxygen billions of years ago. It has no firm cellulose cell wall, which is why its constituents are easily accessible to the body. Its hallmark is phycocyanin, a blue plant pigment that gives spirulina its typical blue-green colour.

Chlorella, by contrast, is a true single-celled green alga. Its defining feature is a robust, multi-layered cell wall made of cellulose and sporopollenin. This wall is naturally hard for humans to digest – which is why high-quality chlorella is mechanically "broken open" (known as a cracked cell wall) so the body can reach the interior of the cell. This very wall is also the reason chlorella is regarded as particularly rich in fibre and chlorophyll: it contains the highest chlorophyll content of any commercially used alga.

Nutrient profile: two characters, one green team

Both algae supply plant protein with all the essential amino acids, plus iron, beta-carotene and a wealth of secondary plant compounds. Their emphases, however, differ clearly:

Because the profiles complement each other – spirulina scores on protein and phycocyanin, chlorella on chlorophyll and the fibre from its cell wall – the two are often offered together as tablets.

Why so many people reach for green algae

Spirulina has been used for centuries: the Aztecs harvested it from Lake Texcoco, and around Lake Chad in Africa it is still traditionally processed into dried cakes ("dihé") to this day. In the 1970s spirulina came into focus as a compact plant-based protein source – even the space programme and international nutrition initiatives took an interest in it. Chlorella, in turn, became popular above all in Japan, where for decades it has been among the most widely used dietary supplements of all.

Today many people reach for these algae because they are looking for an uncomplicated, concentrated form of plant nutrients – especially in a diet low in vegetables or on a purely plant-based one. If you want to build out your "green" building block in everyday life, take a look at barley grass and moringa as well – three classics that work well in rotation.

What research is investigating

Spirulina and chlorella are among the most extensively studied microalgae. Science is interested, among other things, in spirulina's blue phycocyanin and its antioxidant properties in the test tube, in the role of the chlorella cell wall as a source of fibre, and more generally in microalgae as a sustainable plant-based protein source for the future. Much of this is active fundamental research. What is established and textbook-solid is that both algae contain notable amounts of protein, iron and chlorophyll. Important for an honest picture: for spirulina and chlorella themselves, no health claims are currently authorised in the EU. We therefore describe them as what they are – nutrient-rich foods – without promising any effects.

Phycocyanin and chlorophyll: the green-and-blue stars

Two pigments make up the characteristic difference between the two algae – and both are more than just colour. Phycocyanin is the blue pigment of spirulina and belongs to the phycobiliproteins, which help cyanobacteria capture light energy. It is so intense that it is even used as a natural blue food colouring. In research, phycocyanin is a fascinating subject of study as an antioxidant in the test tube.

Chlorophyll, in turn, is the green pigment found in chlorella in especially high concentration – higher than in practically any green leafy vegetable. Chlorophyll is the engine of plant photosynthesis; in the human context it is valued above all as a secondary plant compound and for its green colouring power. Anyone deliberately bringing "green" foods into everyday life gets one of the most chlorophyll-rich sources of all with chlorella. Incidentally, both pigments are sensitive to heat and light, which is why gentle processing and dark storage also help determine the quality.

The B12 myth – honestly explained

Time and again you'll read that algae are the plant-based B12 rescue for vegans. That is misleading. Spirulina and chlorella contain predominantly so-called corrinoids, or pseudo-B12 – substances that are counted in laboratory tests but cannot be used by the human metabolism as genuine vitamin B12. Anyone following a vegan diet should therefore supplement B12 in a targeted and reliable way. How to do that is explained in the guide Nutrients for vegans and specifically in Covering vitamin B12 on a vegan diet.

Tablets, powder or capsules – the forms of administration

Green algae come in three main forms, and the choice mainly determines everyday practicality and taste:

A practical tip: if you don't like the algal taste of powder, you can mix it with a fruity, tart base such as pineapple or lemon juice – that masks the green note far better than, say, banana. Start gradually with a small amount and increase over one to two weeks. Some people react sensitively in their digestion at the start, because the algae bring plenty of chlorophyll and fibre with them – a slow start helps prevent this.

Timing and combining in everyday life

There is no fixed "right" time to take algae – they are foods, not a substance tied to a rhythm. Many take them in the morning with breakfast or spread across the day. Because both algae supply iron, it's worth looking at smart combinations: vitamin C improves the absorption of plant-based (non-haem) iron, which is why a glass of orange juice or a squeeze of lemon with a green smoothie makes sense. More on this in Combining vitamin C and iron and Iron: haem vs. non-haem. Coffee and black tea, on the other hand, can inhibit iron absorption – so it's better to drink them with some time in between.

What to look for in terms of quality

With algae, quality is not a nice-to-have but a must, because they can accumulate substances from the water:

• Closed cultivation systems (controlled ponds/tubes) rather than open natural waters.
• Laboratory testing for heavy metals; for spirulina additionally for microcystins.
• For chlorella, a broken-open cell wall – otherwise part of the constituents remain out of reach.
• Organic quality and transparent origin. What the test seal means is explained in Lab-tested: what does that mean?

Sustainability: why microalgae are considered a food of the future

One reason for the continued interest in spirulina and chlorella lies beyond the plate: microalgae are regarded as one of the most resource-efficient protein sources of all. They grow extremely fast, need little land compared with animal protein production and can be cultivated in closed systems without taking up farmland. This is precisely why nutrition research and even the space programme have taken an interest in them for decades. For you as a customer this means: anyone looking for plant-based protein sources for ecological reasons will find a fascinating building block in green algae – provided the quality is right. Further plant-based protein routes are examined in Whey vs. pea protein.

Honestly put in context: what's certain and what's open

What's certain: spirulina and chlorella are concentrated, nutrient-rich foods with plenty of protein, iron and chlorophyll. What's open or still in research is much about the individual effects of the constituents – here it's a matter of separating marketing "miracle algae" language from demonstrable nutrient facts. And what is definitely not true is the B12 myth. As a supplement to a varied diet the algae make sense – but not as a replacement for fresh vegetables and a good B12 supply.

Matching products & further guides

You'll find the two algae combined with us as tablets; individually in the categories Spirulina, Chlorella and in the overview Algae. Fitting further reading: barley grass, moringa, Nutrients for vegans, Covering vitamin B12 on a vegan diet and Nutrients when you eat few vegetables.

Frequently asked questions (FAQ)

Which is better: spirulina or chlorella?

Neither is better across the board – they complement each other. Spirulina supplies particularly high amounts of protein and the blue pigment phycocyanin, while chlorella scores with the highest chlorophyll content and fibre from its cell wall. Anyone who wants both reaches for the combination as tablets.

Can I take spirulina and chlorella together?

Yes, this is in fact common and sensible, because their nutrient profiles complement each other. Many tablets already contain both algae mixed together. Start with a small amount and increase slowly so that your digestion gets used to the green constituents.

Are algae a good B12 source for vegans?

No. Spirulina and chlorella contain predominantly pseudo-B12, which the body cannot use. On a vegan diet you should supplement B12 in a targeted way via a reliable product and not rely on algae.

How do I recognise high-quality algae?

By controlled cultivation in closed systems, transparent origin, organic quality and laboratory testing for heavy metals (for spirulina additionally for microcystins). Chlorella should also have a broken-open cell wall so that its constituents are available.