Spirulina

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By Nikola · Precision Nutrition L1 · Updated 5 November 2026

Spirulina is a blue-green microalga (a cyanobacterium, species such as Spirulina platensis and Spirulina maxima, now often classed as Limnospira) that is dried and sold as a powder or tablets. On paper it looks impressive: 57 g of protein and 28 mg of iron per 100 g. But people eat it by the spoonful, not by the 100 g, so a 7 g tablespoon gives about 4 g of protein and 2 mg of iron. It is best seen as a concentrated food or supplement that adds some nutrients to a diet, not as a replacement for meals. Quality matters: algae products can be contaminated with toxins from other cyanobacteria, so buy from a producer that tests every batch.

Spirulina nutrition per 100 g and per tablespoon

Nutrient	Dried spirulina, 100 g	1 tablespoon, 7 g
Energy	290 kcal	20 kcal
Protein	57.5 g	4.0 g
Fat	7.7 g	0.5 g
Carbohydrate	23.9 g	1.7 g
Fibre	3.6 g	0.3 g
Iron	28.5 mg	2.0 mg
Copper	6.1 mg	0.43 mg
Magnesium	195 mg	14 mg
Potassium	1360 mg	95 mg
Sodium	1050 mg	74 mg
Thiamin (B1)	2.4 mg	0.17 mg
Riboflavin (B2)	3.7 mg	0.26 mg
Niacin (B3)	12.8 mg	0.9 mg
Vitamin B12	0 µg	0 µg

Source: USDA FoodData Central, SR Legacy: “Seaweed, spirulina, dried” (FDC 170495), checked 5 November 2026. The 7 g tablespoon is a USDA portion; the portion column is calculated. The record also lists 120 mg calcium, 2.1 g polyunsaturated fat (of which 0.82 g ALA) and 3.1 g sugars per 100 g. Values rounded.

Against the EU reference intakes (Regulation (EU) No 1169/2011, Annex XIII), one tablespoon gives about 43% of the copper (1 mg), 18% of the riboflavin (1.4 mg), 15% of the thiamin (1.1 mg) and 14% of the iron (14 mg). The protein, 4 g, is about 8% of the 50 g reference intake: useful, but less than the 17 g in 100 g of firm tofu.

Glycemic index

Spirulina is not listed in the international GI tables (Atkinson 2008). At the amounts people use, a tablespoon carries less than 2 g of carbohydrate, so its effect on blood sugar is negligible.

Health benefits: what the evidence says

• A safety-reviewed food ingredient. The US Pharmacopeia’s dietary supplement expert committee reviewed clinical trials, animal studies, regulatory sources and 31 adverse event reports, and gave Spirulina maxima and S. platensis a Class A safety rating, which allows quality standards for them to be published (Marles et al., 2011). This rating is about quality and safety, not about health effects.
• Iron and copper. A tablespoon adds 2 mg of iron. Under EU rules iron contributes to normal formation of red blood cells and haemoglobin and to the reduction of tiredness and fatigue (Regulation (EU) No 432/2012).
• Not a vitamin B12 source. Spirulina is often sold to vegans for B12, but the USDA record lists 0 µg. The NIH Office of Dietary Supplements notes that natural food sources of B12 are limited to animal foods and that people who eat no animal products should rely on fortified foods or B12 supplements.
• Protein, with perspective. By weight, spirulina is over half protein. In real servings it adds a few grams, so it complements protein foods such as lentils, tofu or Greek yogurt rather than replacing them.

How to eat it

• Start small. Spirulina has a strong, sea-like taste. Begin with half a teaspoon and work up to a teaspoon or a tablespoon.
• Smoothies: blend it with banana, blueberries or spinach, which mask the taste and the colour.
• Stir into food: mix a little into yoghurt, salad dressings, hummus or energy balls with dates and nuts.
• Tablets: follow the dose on the label of the product you buy and do not combine several algae products.
• Buy carefully: choose spirulina from a producer that states it tests for microcystins and other contaminants. Keep it in a closed container, away from light and moisture.

Who should be careful

• Contamination. Spirulina products may contain cyanotoxins, including microcystins, which damage the liver, when other cyanobacteria grow in the culture (Pinchart et al., 2023). A French study of small farms found microcystin levels within the safe regulatory limit, which shows that testing works. MedlinePlus describes contaminated blue-green algae products as likely unsafe, especially for children.
• Phenylketonuria (PKU). MedlinePlus advises people with PKU to avoid Spirulina products.
• Autoimmune disease and immune-suppressing drugs. According to MedlinePlus, blue-green algae might make the immune system more active, so people with autoimmune conditions should avoid them, and they may reduce the effect of drugs such as azathioprine, cyclosporine or prednisone.
• Blood thinners. MedlinePlus also notes that blue-green algae might slow blood clotting, which matters if you take warfarin, aspirin or similar medicines.
• Pregnancy, breastfeeding and children. MedlinePlus says not enough is known about use in pregnancy and breastfeeding, and advises avoiding it. Children are more sensitive to contaminated products.

Traditional view (Ayurveda)

Spirulina is a modern food, but Usha and Vasant Lad’s food guidelines list it as favourable for all three doshas. This is a traditional view, not a clinical finding.

Related entries and articles

• Tofu – a plant protein you can eat by the portion
• Spinach and kale – green foods with iron and folate
• Chia seeds
• Omega-3 fatty acids
• Foods for energy without caffeine
• Plant-based meals for weight loss

FAQ

Does spirulina contain vitamin B12?

Not in a form you can count on. The USDA record for dried spirulina lists 0 µg of vitamin B12, and the NIH Office of Dietary Supplements points vegans to fortified foods or B12 supplements instead.

Is spirulina safe?

Spirulina itself received a Class A safety rating from the US Pharmacopeia’s expert committee. The main risk is contamination with toxins from other cyanobacteria, so buy tested products. Avoid it if you have phenylketonuria or an autoimmune disease, and talk to your doctor if you are pregnant, breastfeeding or take immune-suppressing drugs or blood thinners.

How much protein is in a spoon of spirulina?

About 4 g in a 7 g tablespoon, based on USDA data. That is less than 100 g of tofu (17 g) or a portion of Greek yoghurt, so treat spirulina as an addition, not as your main protein.

Sources

1. USDA FoodData Central, SR Legacy: Seaweed, spirulina, dried (FDC 170495). fdc.nal.usda.gov
2. Marles RJ, Barrett ML, Barnes J et al. United States Pharmacopeia safety evaluation of spirulina. Crit Rev Food Sci Nutr 2011;51(7):593-604. Europe PMC
3. Pinchart PE, Leruste A, Pasqualini V, Mastroleo F. Microcystins and cyanobacterial contaminants in the French small-scale productions of spirulina (Limnospira sp.). Toxins 2023;15(6):354. PMC
4. MedlinePlus Supplements: Blue-green algae (last reviewed 14 February 2015; archived copy). e-lactancia.org
5. NIH Office of Dietary Supplements: Vitamin B12, fact sheet for health professionals. ods.od.nih.gov
6. Regulation (EU) No 1169/2011, Annex XIII (reference intakes). legislation.gov.uk
7. Regulation (EU) No 432/2012, authorised health claims (iron). legislation.gov.uk
8. Atkinson FS, Foster-Powell K, Brand-Miller JC. International Tables of Glycemic Index and Glycemic Load Values: 2008. Diabetes Care 2008;31(12):2281-2283. PMC
9. Lad U, Lad V. Food Guidelines for Basic Constitutional Types, from Ayurvedic Cooking for Self-Healing, 2nd ed. The Ayurvedic Institute. ayurveda.com

This page is for information only and is not medical or dietary advice.