Spirulina Nutrition: Protein, Iron and Calories per Serving

Spirulina contains protein, iron and other nutrients. What it contributes to your day depends on the format and the number of grams you use. A per-100 g figure gives you a common basis for comparison; calculating your portion turns it into a practical amount.

For example, 3 g of the generic dried Spirulina in the USDA FoodData Central reference provides approximately 1.72 g protein, 0.86 mg iron and 8.7 kcal. This is an illustrative calculation from one historical reference dataset, rather than a suggested dose or an analysis of ALPHYCA or every current Spirulina product.

The principle is simple: per-100 g data describe nutrient concentration, while a portion calculation describes what you consume. Keeping those two figures separate makes any Spirulina nutrition label easier to read.

Spirulina nutrition per 100 g and per 3 g

The table below uses the USDA entry for dried Spirulina, published as an SR Legacy historical reference. Each 3 g value is the corresponding per-100 g figure multiplied by 0.03. Results are rounded for readability.

“Carbohydrate, by difference” is the USDA dataset's calculation category. It is not an exact declaration for a UK product, and the energy figure should not be reconstructed with a simple 4/4/9 calculation: This USDA record uses nutrient-specific energy conversion factors.

Composition also varies between Spirulina products. A study of commercial microalgal biomass reported an average protein content of 48 ± 4% in the Spirulina samples it tested, with variation between producers (Muys and colleagues). For the product you use, its own declaration should take priority over a generic database.

What does the protein number really mean?

Protein density is the amount of protein relative to a product's weight. Protein per portion is the amount in the quantity you actually consume. Spirulina can be protein-dense and still make a compact contribution when the portion is small.

In the USDA dried reference, protein accounts for 57.47 g per 100 g. Applied to 3 g, that becomes 1.7241 g, displayed as 1.72 g. That is a small addition to your daily protein intake, alongside the foods you eat in larger portions.

For a wider introduction to the organism and its composition, see the UK guide to what Spirulina is, its benefits and safety.

How to calculate nutrients for your own portion

Use the following calculation for any nutrient declared per 100 g:

Nutrient in your portion = per-100 g value × portion weight in grams ÷ 100

For protein in the 3 g example:

57.47 g × 3 ÷ 100 = 1.7241 g protein, rounded to 1.72 g.

The method works for milligrams, kilocalories and kilojoules too, provided you keep the unit unchanged. For iron:

28.5 mg × 3 ÷ 100 = 0.855 mg iron, rounded to 0.86 mg.

If your chosen product lists a different protein or iron figure, use that figure. Formulations and blends can have their own declarations, so a generic Spirulina entry may be the wrong basis. Weigh or measure the portion according to the product instructions; a particular spoon does not always hold a fixed number of grams. If you are still deciding how much to use, the guide to how much Spirulina per day explains why there is no single amount for everyone and how to follow labelled directions.

Why fresh and dried figures are different

Fresh and dried Spirulina cannot be compared gram for gram without accounting for water. The USDA's separate generic entries illustrate the scale of the difference: its raw Spirulina reference lists 90.67 g water per 100 g, while its dried reference lists 4.68 g water per 100 g.

These are separate database entries rather than the same batch measured before and after drying, so they do not provide a conversion rule for ALPHYCA Fresh, Nibs or any other named product. They illustrate why water basis matters: the more of a format's weight that comes from water, the less concentrated its nutrients will usually appear per gram.

The most useful comparison therefore starts with each format's own label. Check whether the data refer to 100 g, a stated portion or a prepared product, then compare like with like.

ALPHYCA puts this format choice into practice through controlled Spirulina cultivation. ALPHYCA Fresh Spirulina is its flagship, minimally transformed chilled format, while ALPHYCA Spirulina Nibs is gently dehydrated at low temperature into a distinctive, convenient shelf-stable format.

Explore the two formats to see which better fits your routine. For nutrient calculations, use the nutrition declaration supplied with the product, where available: the USDA examples above are not analyses of either ALPHYCA product.

How should you interpret Spirulina's iron?

The dried USDA reference contains 28.5 mg iron per 100 g, yet the illustrative 3 g portion provides about 0.86 mg. This is a good example of why a striking per-100 g number needs portion context.

The figure describes iron present in the material, not the amount absorbed by an individual. Absorption depends on the wider meal and personal factors, and a nutrition calculation cannot diagnose or treat low iron. Anyone concerned about symptoms, iron status or anaemia should speak with their GP rather than using Spirulina as a substitute for assessment or prescribed care. The NHS explains how iron deficiency anaemia is assessed and treated.

Nutrient content and demonstrated health outcomes are related but different questions. Our guide to Spirulina benefits keeps those evidence levels separate.

Can Spirulina be relied on for vitamin B12?

No. Spirulina should not be treated as a dependable source for meeting vitamin B12 needs.

Research on tested Spirulina tablets found that pseudovitamin B12, an inactive analogue, predominated and that the assay method strongly influenced the measured value (Watanabe and colleagues). This does not mean every product contains zero active B12, but a Spirulina B12 figure without information about its active forms is not a reliable basis for dietary planning.

The NHS guidance on a vegan diet lists dependable sources such as fortified breakfast cereals, fortified soya drinks and fortified yeast products, and notes that a supplement may be needed. If your intake is uncertain, use a reliable source and seek professional advice where appropriate.

Three checks that make any Spirulina label more useful

Before comparing products or formats, check:

• The source of the figures. A product declaration or batch analysis is more relevant to that product than a generic database entry.
• The basis. Confirm whether the values refer to dried material, a fresh format, a blend or a prepared product.
• The portion. Convert the per-100 g figure using the number of grams you actually use, keeping the original unit.

Spirulina brings protein, natural pigments and micronutrients together in a compact amount. These three checks keep the comparison tied to the format and quantity you actually use.

Frequently asked questions

How much protein is in 3 g of Spirulina?

The USDA dried reference works out to approximately 1.72 g protein in 3 g. Your product may differ, so calculate from its own declaration when available.

How many calories are in 3 g of Spirulina?

The same generic dried reference provides 8.7 kcal, or approximately 36.4 kJ, in 3 g. This is an example rather than a guaranteed figure for every format or formulation.

Is fresh Spirulina nutritionally equivalent to dried Spirulina gram for gram?

No direct equivalence should be assumed. Fresh material generally contains much more water, so compare the declarations for the specific formats rather than applying a generic conversion.

Can I rely on Spirulina for vitamin B12?

No. Spirulina can contain inactive B12 analogues, so use dependable sources such as appropriately fortified foods or a suitable supplement for B12 planning.

Is 3 g the ideal daily amount?

No universal dose is established by this calculation. The 3 g figure is simply an illustration; follow the directions for your chosen product and consider professional advice if you have a medical or nutritional concern.

Use the numbers for your own portion

Take the per-100 g declaration from your chosen format, weigh the portion you actually use and run the calculation once. You will then have a clear picture of what that amount of Spirulina contributes to your routine.