Chlorella and spirulina turn up in almost every "green" or "detox" blend, wrapped in superlatives. Both are genuinely interesting foods. Both are also sold with claims that run well ahead of what is permitted or proven. Here is the straight version.
This is part of our guide to choosing a seaweed and sea-greens supplement.
What they actually are
Spirulina is a blue-green algae (technically a cyanobacterium), grown in fresh water. It is around 60–70% protein by weight and contains iron, B vitamins and the blue-green pigment phycocyanin.
Chlorella is a green freshwater algae with a tough cell wall that has to be broken for us to digest it — so "cracked cell wall" chlorella is the form to look for. It is dense in chlorophyll, protein, iron and other nutrients.
Both are, essentially, concentrated whole foods. That framing matters, because it is also the honest basis for taking them.
What the labels can and cannot say
Here is the part the "superfood" marketing skips: neither chlorella nor spirulina has an authorised health claim in Great Britain. A seller may describe them and list what they contain, but may not lawfully claim they detoxify, boost immunity, or bind heavy metals — those would be unauthorised health claims.
Where these products can make a claim is through their nutrient content. If a serving provides a meaningful amount of a nutrient with an authorised claim — iron, for example — that claim applies: iron contributes to the reduction of tiredness and fatigue. That is a claim about the iron, not about the algae's mystique.
So a page promising that chlorella "flushes toxins" or "detoxifies heavy metals" is outside the rules, and the human evidence for those specific claims is limited whatever the marketing implies.
The honest case for taking them
Stripped of hype, algae are a legitimately useful addition for some people:
- Plant-based protein and iron — genuinely useful for vegans and vegetarians, where both can be harder to get.
- A concentrated whole-food nutrient source — a convenient way to add nutrient density if your vegetable intake is patchy.
- Chlorophyll and B vitamins — present in meaningful amounts.
That is a reasonable, modest proposition — and modest is the point. You are adding a nutrient-dense food, not detoxifying your organs.
How to choose one worth taking
- Source and testing. Algae absorb whatever is in their growing water, including heavy metals, and spirulina from poorly controlled sources can be contaminated with microcystin toxins. Buy from a supplier that tests. Organic certification helps. (It is also worth knowing that spirulina and chlorella naturally contain sulphites, which are a declarable allergen.)
- Cracked cell wall (chlorella). Without it, you absorb far less.
- Quantity. Meaningful amounts, not a fairy dusting to justify a green label.
- Realistic claims. If the page promises detox or dramatic outcomes, be sceptical of the rest of it too.
A note on algae and iodine
Spirulina and chlorella are freshwater algae and are not significant iodine sources — that comes from seaweed, a marine algae, which is a different thing. If you see "algae" on a label, check whether it means freshwater greens (protein, iron) or seaweed (iodine), because they do different jobs. Our guide to iodine and thyroid function covers the seaweed side.
Where ours fits
Our Organic Seaweed Complex combines organic spirulina and chlorella with organic seaweed, artichoke, green tea, alfalfa and cayenne — pairing freshwater greens (protein, chlorophyll, iron) with a controlled marine iodine source in one Soil Association certified capsule.
We describe what is in it and let the ingredients speak. The benefit claims we make are the authorised ones for its nutrients — for example, iodine contributes to the normal production of thyroid hormones and normal thyroid function. We do not claim the algae detoxify anything, because that is not a permitted claim and the evidence would not support it. (This product contains naturally occurring sulphites.)
Read next: how to choose a seaweed supplement and iodine and thyroid function explained. Or browse our Energy & Vitality range.
Always read the label. Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle.
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