Spirulina

Spirulina (Arthrospira platensis)

Spirulina (in Hebrew, “ספירולינה”) is a cyanobacterium — a photosynthetic bacterium, not an alga in the plant sense — and one of the most nutrient-dense foods ever measured: 57 grams of protein, 28 mg of iron and 6 mg of copper per 100 grams of dry weight.

And that is where the central problem with all its marketing lies. Nobody eats 100 grams of spirulina. A typical serving is 3-10 grams. When you translate the impressive numbers into a realistic serving, the picture changes completely — and it’s worth seeing it before you buy.

On this page: what spirulina really provides in a serving, what is proven and what isn’t, and three safety caveats worth knowing.

Nutrition facts — per 100 grams vs. a real serving

The numerical conclusion: a tablespoon of spirulina provides about 3 grams of protein — less than half an egg. It is not a practical source of protein, and marketing that touts “60-70% protein” relies on a number nobody consumes.

What is meaningful in a serving: copper (34%), riboflavin (14%), iron (8%), and phycocyanin — the blue pigment that is the truly interesting active ingredient.

Vitamin B12 — the most dangerous mistake

This is the most important caveat on this page, and it is a matter of health, not of nutritional precision:

Spirulina contains “pseudo-vitamin B12” — analogues that are inactive in the human body. In standard lab tests they are counted as B12, which is why an impressive value appears on many packages. But the body cannot use them, and there is evidence they may compete for binding sites and interfere with the absorption of real B12.

What this means: vegans and vegetarians cannot rely on spirulina as a source of vitamin B12. B12 deficiency causes neurological damage that may be irreversible. The only solution is a dedicated B12 supplement or fortified food.

What is proven and what isn’t

Reasonable evidence:

• Blood lipid profile. Meta-analyses of controlled trials found a moderate drop in total cholesterol, LDL and triglycerides with spirulina at doses of 1-8 grams a day. The effect exists but is not dramatic.
• Blood pressure. Preliminary evidence of a slight reduction, mainly at relatively high doses.
• Phycocyanin as an antioxidant. Its biochemical activity is well documented in the lab.

Weak or early evidence:

• Immune function — mainly lab and animal studies.
• Seasonal allergy (rhinitis) — a few small trials with positive results, but the samples are small.
• Endurance and sports performance — mixed results.

Unsupported: “detox”, “binding heavy metals”, general strengthening, weight loss.

Three safety caveats

• Microcystins. Spirulina is grown in open ponds, and such ponds can also be colonized by other cyanobacteria — mainly Microcystis — which produce microcystins, hepatotoxic toxins. Market testing has found contamination in some products. The solution: buy from a manufacturer that publishes lab tests for microcystins and heavy metals.
• Phenylketonuria (PKU). Spirulina is very rich in phenylalanine. People with PKU must not take it.
• Autoimmune diseases. Because of its reported effect on the immune system, there is a theoretical concern about worsening autoimmune diseases. The evidence is limited, but it is a reason to consult a doctor.

Benefits

• High micronutrient density for its weight. Copper, riboflavin and iron in noticeable amounts even in 5 grams.
• Phycocyanin: a unique antioxidant that is also the source of the blue color. It is also used as a natural food coloring.
• Protein with a good profile — it contains all the essential amino acids, even though the amount in a realistic serving is small.
• Reasonable evidence for the lipid profile — as detailed above.
• Plant-based iron in a reasonable amount — 1.4 mg in a 5-gram serving.
• Low environmental footprint — grown in water, with no farmland and no animal feed.
• An alternative to moringa powder in the category, with a different mineral profile.

Downsides and considerations

• The gap between marketing and the serving. Almost every claim about spirulina is framed per 100 grams, an amount nobody consumes.
• Pseudo-vitamin B12 — as detailed above, the most serious caveat.
• Microcystins, PKU and autoimmunity — as detailed above.
• Price. Very expensive relative to the nutritional value it actually provides. The same money spent on spirulina would buy a large quantity of lentils, eggs or leafy greens.
• Taste and smell. Strongly earthy and marine, which many people struggle with. Well hidden in a fruit smoothie with banana.
• Vitamin K in an amount relevant to people taking anticoagulants — keep intake consistent.
• A supplement, not a food. It doesn’t replace a vegetable, a protein or a meal, and it doesn’t “fix” a poor diet.

Practical use

• Typical dose: 1-5 grams a day (half a teaspoon to a level teaspoon). Higher doses have been studied but are not needed.
• Choose a brand that publishes tests for microcystins and heavy metals. This is the most important check in the category.
• Don’t rely on it for B12. Vegans need a dedicated supplement.
• Mix it into a smoothie with banana, berries or citrus juice — the tartness and sweetness mask the taste.
• With vitamin C — improves absorption of its plant-based iron.
• Not close to coffee or tea — tannins inhibit iron absorption.
• Consult a doctor if you have an autoimmune disease, are on anticoagulant treatment, or are pregnant or breastfeeding.
• Keep things in proportion. If the goal is protein — one egg gives twice as much as a tablespoon of spirulina, at a tenth of the price.

Summary

Spirulina is a dense and genuinely interesting food, mainly thanks to phycocyanin, copper and riboflavin — along with reasonable evidence for a moderate improvement in the lipid profile. But it is not a practical source of protein: a tablespoon provides about 3 grams, less than half an egg. And the most important caveat of all: its B12 is not bioavailable — vegans who rely on it may develop a deficiency with neurological damage. Before buying, it’s worth checking one thing: that the manufacturer publishes tests for microcystins and heavy metals.