What they actually are
The most important distinction is taxonomic: spirulina is a cyanobacterium — a prokaryote, a photosynthetic bacterium — not an alga at all, despite being sold in the “algae” section. Chlorella is a true alga, a eukaryote with a proper nucleus, chloroplasts, and a tough outer cell wall.
That cell wall matters practically: raw chlorella passes through the human gut largely undigested. Reputable chlorella products are “cracked-wall” — mechanically processed to open the cell wall before drying. Spirulina’s cell walls are thin and soft, so no such processing is needed.
Nutrient profiles: where they overlap and diverge
At a rough comparison per 10 grams of dried biomass:
| Nutrient | Spirulina | Chlorella |
|---|---|---|
| Protein | 6–7 g (all essential AAs) | 5–6 g (all essential AAs) |
| Iron | ~28 mg (non-haem) | ~13 mg (non-haem) |
| Chlorophyll | ~1% by weight | ~3% by weight (3× more) |
| Phycocyanin | 12–20% by weight | Absent |
| B12 analog | Pseudocobalamin (inactive) | CGF contains active B12 precursors |
| Omega-3 (ALA) | ~160 mg | ~140 mg |
| CGF | Absent | Present (cell-repair factor) |
Values are approximate and vary by producer, drying method, and harvest conditions.
The case for spirulina
- Phycocyanin.Spirulina’s signature blue pigment is a potent anti-inflammatory and antioxidant with no equivalent in chlorella. It’s the compound behind most of spirulina’s clinical effects on cholesterol, blood pressure, and allergic rhinitis.
- Iron.Spirulina has roughly twice the iron of chlorella per gram, and the form is reasonably bioavailable. Multiple RCTs in iron-deficient populations have shown measurable improvements. This is spirulina’s strongest clinical use case, and chlorella cannot match it.
- No cell wall processing needed.Digestibility from powder or tablet is high out of the box. No need to verify “cracked-wall” claims.
- More clinical research. Spirulina has a larger and more consistent body of human trial evidence than chlorella at the time of writing.
The case for chlorella
- Higher chlorophyll. Chlorella has approximately three times the chlorophyll content of spirulina. Chlorophyll has plausible (though not clinically proven) benefits for gut motility, detoxification support, and wound healing. It also gives chlorella its distinctive earthy taste.
- Chlorella growth factor (CGF).A complex of nucleotides, peptides, and polysaccharides found only in chlorella. CGF has shown cell-repair and immune-modulating properties in some studies. It’s one of chlorella’s more distinctive compounds.
- Heavy metal binding.The cell wall of chlorella has plausible (mechanistic, not strongly clinical) affinity for certain heavy metals in the gut. It’s been studied as an adjunct for lead and mercury detox with modest results.
- Omega-3 profile. Roughly comparable to spirulina, but chlorella also contains EPA and DHA in small amounts — making it marginally better for vegans seeking marine omega-3s from algae.
The B12 question
Neither spirulina nor chlorella is a reliable B12 source for vegans.
Spirulina contains pseudocobalamin — a B12 analog that competes withreal B12 for absorption and doesn’t perform B12’s metabolic functions. Relying on spirulina for B12 is actively counterproductive.
Chlorella contains more active B12-like compounds and some studies have shown modest improvements in serum B12 markers, but the evidence is not strong enough to recommend it as a B12 supplement. If you’re vegan, take methylcobalamin. Neither microalga replaces it.
Can you take both?
Yes — and many dedicated supplement users do. A common split is spirulina (for iron, phycocyanin, protein density, rhinitis) and chlorella (for chlorophyll, CGF, and variety). Combined doses of 3–5 g total per day across both are common in the community.
There is no known antagonism between the two. The main practical constraint is cost — quality products of both aren’t cheap.
Which to choose if you can only pick one
- For iron deficiency: spirulina. Unambiguously better by the research and per-gram iron content.
- For allergic rhinitis: spirulina. The clinical evidence is specifically for spirulina; chlorella has no comparable data.
- For cholesterol and blood pressure: spirulina. Again, the phycocyanin-related research is more consistent.
- For detox / heavy metals: chlorella. The cell-wall binding mechanism is chlorella-specific.
- For general nutritional density and versatility: spirulina has the edge on protein and iron; chlorella has more chlorophyll. For a healthy adult eating a varied diet, the difference is small.
Quality rules apply to both
Everything on our quality & puritypage applies to chlorella too. Heavy metal contamination, microbial testing, drying method — the same criteria matter. Chlorella’s tighter cell wall makes it marginally more resistant to some contaminants, but that’s no reason to skip the CoA.
See our brand directory for spirulina producers we trust, and our research library for the underlying studies.