21 juin 2025

Swiss freshwater algae: what spirulina actually gives you in the kitchen

A level teaspoon of spirulina powder weighs about 3 grams. Using the USDA composition table, that comes to 1.7 g of protein, 0.86 mg of iron and 8.7 kcal. Roughly a small handful of pumpkin seeds. Almost everything else written about these green powders follows from that arithmetic, and most articles skip it.

Two more things need saying straight away, because most guides on the subject get both wrong. Spirulina is not an alga. It is a cyanobacterium of the genus Limnospira, formerly Arthrospira. And nobody fishes it out of a Swiss lake. It grows naturally in warm water, around 25 °C, and strongly alkaline water, between pH 8 and 11.5, in the lakes of intertropical regions such as Chad, Ethiopia and Mexico. What is produced in Switzerland grows in heated closed ponds or photobioreactors. Nothing shameful about that, but it does dismantle the story of a local ingredient gathered at the water’s edge.

What the word “algae” covers, and why it matters here

In everyday speech, anything green and aquatic is an alga. In biology the line is sharp, and it has practical consequences.

Chlorella is a genuine microalga: a eukaryotic organism with a nucleus and chloroplasts, like a plant. Its cell wall is made of cellulose, which the human gut does not break down. That is why almost every product on sale states that the wall has been cracked or mechanically broken. Without that step, most of the cell contents pass through the intestine unreleased. An animal study cited in the 2020 Nutrients review on chlorella measured more than 80 % protein digestibility once the wall had been ruptured. If the packaging says nothing about the cell wall, that is missing information rather than a minor detail.

Spirulina is a photosynthetic bacterium. It has no cellulose wall, which is why it is eaten as it comes: dried, then powdered or flaked, with no mechanical pretreatment.

That difference in biology also explains one reasonable worry and one reassuring answer. Cyanobacteria are the group behind the cyanotoxins found in lake blooms. A genomic study published in iScience in 2024 compared 22 genomes of the genus Limnospira and found no cyanotoxin synthesis genes at all. The genus itself does not make microcystins. Where risk exists, it comes from a pond being contaminated by other cyanobacteria, not from spirulina itself. That distinction is useful: it moves the question away from the species and onto the quality of production control.

Why nobody harvests Swiss lakes

Scooping green filaments out of a lowland lake sounds appealing. Field data discourage it.

A five-year monitoring campaign on Lake Greifensee, published in Environmental Science & Technology in 2024, covered 150 sampling dates and 850 samples. Microcystins were present in 70 % of samples and anabaenopeptins in 95 %. Concentrations in lake water stay low, on the order of tens of nanograms per litre for the most abundant microcystin, but biomass concentrates whatever the water holds. The WHO tolerable daily intake for microcystins is 0.04 micrograms per kilo of body weight per day, or 2.6 micrograms for a 65 kg adult. Harvesting yourself means eating a mixed biomass that nobody has analysed and whose species composition shifts week by week.

The klamath case makes the problem concrete. Aphanizomenon flos-aquae is the one edible cyanobacterium commonly sold that genuinely comes from a wild lake, Klamath Lake in Oregon. A screening study published in Foods in 2025, covering twelve cyclic peptide cyanotoxins, detected several of them in a klamath-based supplement, with high concentrations of microcystin-RR. The same work made no such finding in cultivated spirulina products. The difference is not the species on the label, it is the growing environment: controlled pond versus open lake.

What a culinary dose actually delivers

The figures in circulation are per 100 grams of dry matter. Nobody eats 100 g of spirulina. Here is the USDA table for dried spirulina, scaled to the amounts people really use.

Per 100 g dry	Per 3 g (1 tsp)	Per 10 g
290 kcal	8.7 kcal	29 kcal
57.5 g protein	1.7 g	5.8 g
28.5 mg iron	0.86 mg	2.85 mg
120 mg calcium	3.6 mg	12 mg
195 mg magnesium	5.9 mg	19.5 mg
1050 mg sodium	31.5 mg	105 mg
2.08 g polyunsaturated fat	0.06 g	0.21 g
0.0 µg vitamin B12	0 µg	0 µg

Three things follow. A teaspoon covers roughly 6 % of the daily iron requirement of a woman aged 19 to 49, which the NHS sets at 14.8 mg. Not nothing, but not the answer to a deficiency either. Matching the protein in one egg takes about 10 g of powder, three teaspoons, which is already a lot to taste. And sodium climbs faster than people expect: 10 g brings as much sodium as a generous pinch of salt, which matters if you then season the dish as usual.

A word on variability, because it is enormous and rarely mentioned. The 2025 review in Life gathers protein measurements for Arthrospira platensis: anywhere from 17 % to 80 % of dry matter depending on strain, growth medium, light, temperature and harvest phase. The thirteen chlorella products analysed in the 2020 Nutrients review reported iron contents ranging from 10 to 1600 mg per 100 g. A composition table gives you an order of magnitude, not the value of the tub on your shelf.

The awkward part: vitamin B12

This is the most widespread error, usually committed with nothing more than a parenthetical caveat about bioavailability. The reality is blunter.

Analyses of spirulina tablets show that the dominant cobamide is not vitamin B12 but pseudovitamin B12, 7-adeninyl cyanocobamide, which is biologically inactive in humans. The review by Watanabe and colleagues published in Nutrients in 2014 concludes explicitly that edible cyanobacteria and their products are not suitable as a vitamin B12 source for vegetarians. The measurement method makes things worse: standard microbiological assays count pseudovitamin as B12, which produces labels claiming tens of micrograms for an active content near zero. The USDA, which uses different methods, lists 0.0 micrograms for dried spirulina.

Chlorella is a different and more nuanced case. It does contain genuinely active B12, but the same group reports contents ranging from zero to several hundred micrograms per 100 g of dry matter depending on the brand, with no documented explanation for the spread. In other words: one chlorella may contain some, yours may not, and nothing on the packaging settles it.

The practical conclusion is not ambiguous. If you are vegetarian or vegan, your B12 comes from a supplement or fortified foods, not from a green powder. Our page on vitamin B12 needs and reliable sources covers the forms and dosing schedules.

Iron: content is not absorption

Iron is the strongest argument for these powders, and it deserves to be presented properly.

On content, the gap between species is huge. Work published in Food Chemistry in 2025 measured anywhere from 0.71 mg per 100 g in Dunaliella salina to 299 mg per 100 g in Tetraselmis chui. But content says nothing about what gets absorbed. The same team, writing in Current Research in Food Science in 2026, put nine microalgae samples through standardised in vitro digestion and then a Caco-2 cell model: iron bioaccessibility ranged from 0.5 % in Tetraselmis chui to 83.4 % in a green Chlorella vulgaris. Arthrospira platensis came out with the best iron bioavailability, comparable to ferrous sulphate.

That is a good result, and it should be read for what it is: a cell model, not a human trial. On the clinical side, a systematic review in Molecular Nutrition & Food Research in 2025 pulled together 32 in vivo studies, seven of them human. It reports improvements in haemoglobin and ferritin with both spirulina and chlorella, no significant adverse effects, and concludes that longer human trials are needed to establish dosing. Improvement seen in short studies is not proof of therapeutic efficacy.

The most reliable lever lies elsewhere: vitamin C at the same meal, and keeping tea and coffee away from it, which we detail in our guide to optimising plant iron absorption.

Protein: good quality, small quantity

On quality, spirulina delivers. All nine essential amino acids are present. Methionine and cysteine are limiting but sit above 80 % of the FAO reference level. The DIAAS score reported for Arthrospira platensis is 85.2, against 56.6 for chickpea and 57.7 for mung bean. For a plant source, that is very good.

One industrial detail is worth knowing: drying method matters. Drum drying on hot rollers cuts methionine content by around 30 % compared with spray drying. Few producers mention it, but when the information appears on a manufacturer’s site it tells you more than most marketing claims.

Then there is quantity. At 1.7 g of protein per teaspoon, these powders are not a protein source, they are a nutritional condiment. Volume comes from pulses, tofu, wholegrains and nuts, as set out in our plant protein guide.

What the clinical trials show, and at what dose

There is a real clinical literature here, and it is more modest than the brochures.

A meta-analysis published in the Journal of Human Nutrition and Dietetics in 2025 pooled 29 randomised trials and 1583 participants. Eating edible algae reduced systolic blood pressure by 2.05 mmHg (95 % CI −3.80 to −0.31) and diastolic by 1.87 mmHg. Spirulina did better than average, at −5.28 and −3.56 mmHg. The effect appeared from 3 g a day over at least twelve weeks, and was larger in people at cardiometabolic risk. Heterogeneity between studies was high, with an I² of 75 % for systolic pressure.

Another meta-analysis, in Nutrients in 2025, reaches a distinctly cooler conclusion: chlorella is neutral on blood pressure and lipids, and spirulina lowers diastolic pressure by just 0.42 mmHg, an effect the authors themselves call small and of uncertain clinical significance. Both papers are serious and they disagree. When two meta-analyses from the same year fail to converge, caution is not a pose, it is the correct reading.

One practical point follows: 3 g a day, every day, for three months is a supplementation protocol, not a pinch in a Sunday smoothie. If the goal is cardiovascular, it belongs in a conversation with a health professional and in our page on dietary supplements for vegetarians, not in a recipe.

Safety: what ANSES says

The July 2017 opinion from the French food safety agency ANSES on supplements containing spirulina is the most useful document available on the subject. It deals with risk rather than nutritional merit, which makes it unusually readable.

The agency had received 49 reports of adverse effects up to February 2017, ten of them documented well enough for causality analysis. Digestive upset dominates. Isolated cases of muscle injury, hepatitis and allergic reaction, including one facial angioedema, were reported without any dose relationship being established.

On contaminants the conclusion is clear: products containing spirulina can be contaminated by cyanotoxins, by bacteria or by trace metals, and the agency recommends choosing the supply chains most closely controlled by public authorities, with traceability and an identifiable manufacturer. Spirulina’s phycobiliproteins are strong chelators, and its metal content correlates directly with the quality of the culture water. European rules set 3 mg/kg lead, 1 mg/kg cadmium and 0.1 mg/kg mercury for supplements; the USP monograph is stricter, at 1 mg/kg lead, 0.5 for cadmium and mercury and 1 for arsenic. Some published analyses exceed those values.

Three points that get read less often:

Beta-carotene. Five grams of spirulina a day, the maximum some supplements recommend, supplies 7 to 8.5 mg of beta-carotene, while the estimated daily limit from supplements is 7 mg. A methodological aside worth noting: the USDA credits its dried spirulina with only 29 µg of retinol equivalent per 100 g, far below those figures. That gap between databases is not an error in either one, it is genuine batch variability.

Phenylketonuria. Spirulina contains phenylalanine, 2.777 g per 100 g according to the USDA. It is not recommended for people with phenylketonuria.

Allergy history. Given the reported cases, ANSES advises against spirulina for people with a history of allergy.

Setting contamination aside, the agency considers that spirulina poses no health risk at low doses, up to a few grams a day in adults, while judging that clinical studies are needed to set a maximum daily dose.

Buying and choosing in Switzerland

The Swiss legal framework is the federal ordinance on novel foods (RS 817.022.2). A genuinely new species goes through authorisation by the Federal Food Safety and Veterinary Office; the annex lists what may be placed on the market without authorisation, including anything that may be marketed under EU Regulation 2015/2283. In practice, for a shopper, the label says little and the producer says a lot.

Four questions that sort the field:

Where does the biomass come from and who dried it? A producer who names the cultivation site and the drying method has more to defend than a private label.

Are there batch analyses, and what do they cover? The useful minimum is heavy metals, meaning lead, cadmium, mercury and arsenic, plus microcystins. An analysis that only reports bacterial counts does not answer the question ANSES raised.

For chlorella, is the cell wall cracked? Without that statement, the stated digestibility is not assured.

Is the product sold as a food or as a supplement? The two statuses carry different labelling obligations, and the second requires a recommended daily dose on the pack.

On the gap between marketing promises and data, we devoted a full piece to the question in spirulina and chlorella: superfoods or marketing, and a more detailed buying guide in the microalgae guide.

Reading a batch analysis

Many suppliers mention lab reports without publishing them, and people who do receive one rarely know what to look for. The reference values all sit in the ANSES opinion and take minutes to check.

For heavy metals, European rules for supplements allow 3 mg/kg lead, 1 mg/kg cadmium and 0.1 mg/kg mercury. The USP Dietary Supplements Compendium monograph for Arthrospira platensis is stricter, at no more than 1 mg/kg lead, 0.5 mg/kg each for cadmium and mercury and 1 mg/kg arsenic. A report that stays under the USP figures is a good sign; one that only just meets the European values is not wrong, but it is less comfortable.

For microcystins there is no legal ceiling for spirulina supplements, and ANSES states plainly that such a threshold still needs to be established. The reference point is the WHO tolerable daily intake of 0.04 micrograms per kilo of body weight, which comes to 2.6 micrograms a day for a 65 kg adult. Someone eating 3 g of powder daily stays below that as long as measured contamination is under roughly 0.8 micrograms per gram. That calculation does not substitute for a regulatory limit, but it turns a lab number into something you can act on.

Storage: why green powder turns

Dried microalgae contain polyunsaturated fatty acids, 2.08 g per 100 g in spirulina according to the USDA. Those fats oxidise, and the oxidation products are what give old packets their fishy smell. Light, heat and air speed it up, and a large container opened daily ages faster than a small one. In practice: an airtight opaque jar, a cool cupboard rather than a shelf above the hob, and 100-gram packs rather than the discounted kilo if you use a teaspoon a day. Phycocyanin fades along the way, which shows as a shift from blue-green to dull olive well before the best-before date.

Cooking without ruining the product

Spirulina owes its blue-green colour to phycocyanin, a pigment protein. It is heat-sensitive. Work published in Food Chemistry in 2025 on its degradation shows that heating unfolds it, and that microwave heating degrades it faster and at lower temperatures than conventional conduction, with measurable disruption from 55 °C. That is why a bright green dish turns khaki as soon as you let it simmer.

Three practical consequences.

Add the powder off the heat, after cooking, once the pan has dropped a little in temperature. That applies to risotto, soups and sauces. The taste is better too: heated, the product turns more bitter.

Never microwave a spirulina smoothie to take the chill off. That is the worst of both worlds.

In baking, the ceiling is low. A study published in Foods in 2026 added spirulina to wheat dough at 0 to 4 % of flour weight. Between 1 and 3 %, mixing stability rose from 4.9 to 6.4 minutes and the gluten network stayed continuous; at 4 %, stability dropped and discontinuities appeared under the microscope. In kitchen terms: 9 g maximum per 300 g of flour, and 6 g already gives a decisive colour.

On flavour, the register is not iodised, contrary to what is often written. It is grassy, slightly earthy, with a bitterness that rises with the dose. Acidity disciplines it: lemon juice, vinegar, tomato. Fat rounds it off: olive oil, avocado, tahini. If you want a genuinely marine taste and actual iodine, you want seaweed, which we cover in cooking with dulse, wakame, nori and kombu and in our piece on balancing iodine on a vegetarian diet.

Three calibrated recipes

Green risotto, spirulina off the heat

Serves 4: 300 g arborio rice, 1 chopped shallot, 1 litre hot vegetable stock, 100 ml dry white wine, 2 tbsp olive oil, 60 g microbial-rennet parmesan-style cheese, 6 g spirulina powder, salt and pepper.

Sweat the shallot over low heat, coat the rice until translucent, deglaze with the wine and let it evaporate. Add the stock a ladle at a time over 17 to 18 minutes. Take the pan off the heat, stir in the cheese, wait two minutes for the pan to drop below 60 °C, then add the spirulina and mix. Serve immediately: the colour holds for about ten minutes, then browns. The 6 g spread across four plates comes to 1.5 g each.

Chlorella, walnut and lemon pesto

Makes a 200 g jar: 50 g walnuts or cashews, 20 basil leaves, 1 garlic clove, 60 ml olive oil, 6 g cracked-wall chlorella, juice of half a lemon, salt.

Blend everything cold. The lemon is not decorative: it tempers chlorella’s bitterness, which is more pronounced than spirulina’s. Reckon on one tablespoon per pasta serving, about 0.8 g of chlorella per person. Keeps five days in the fridge under a film of oil.

Chilled cucumber, avocado and spirulina soup

Serves 4: 2 cucumbers, 1 ripe avocado, 250 ml cold vegetable stock, juice of half a lemon, 3 g spirulina, a few mint leaves, salt and pepper.

Blend the peeled cucumber, avocado, stock and lemon. Add the spirulina last, cold, and blend for ten seconds more. Serve well chilled. Since nothing is heated, this is the preparation that best preserves colour and flavour, and 3 g is enough for four bowls.

For other cold uses, our plant-based protein smoothies give bases that carry half a teaspoon well.

Six common mistakes

Relying on spirulina for vitamin B12. It is the only mistake on this list that can have lasting health consequences.

Reading the per-100-gram figures as if they described a serving. A teaspoon is 3 % of that column.

Boiling it. Phycocyanin degrades, the colour turns, the bitterness rises.

Raising the dose because “it’s natural”. Beyond a few grams a day you enter a zone where ANSES considers the data insufficient to set a limit, and where beta-carotene approaches the ceiling used for supplements.

Buying on price alone with no batch analysis. The risk is not the organism, it is what comes with it.

Taking chlorella with no cracked-wall statement, then concluding it does nothing.

Adjusting for different situations

Pregnancy and breastfeeding: with no data allowing a safe dose to be set, and given the risk of metal contamination, regular use is a conversation to have with a health professional.

Phenylketonuria: not recommended, because of the phenylalanine.

Allergy history: advised against by ANSES in light of the reported cases.

Children: studies in undernourished children used 5 g a day with no adverse effects reported, but in a supervised refeeding context. In an ordinary Swiss diet there is no identified need.

Athletes and heavy protein eaters: the benefit is marginal given the quantities involved, as our page on the vegetarian high-protein diet explains.

People on anticoagulants: chlorella contains vitamin K1, at levels varying between products from 0.3 to 3.5 mg per 100 g across the thirteen products analysed in the 2020 review. Once intake becomes regular, it is worth telling the doctor who monitors your INR.

Limits of the available data

No single composition figure is valid for the product in your hand: the batch-to-batch spread runs tenfold for iron, and from 17 to 80 % for protein.

The disagreement between the two 2025 meta-analyses on blood pressure cannot be settled. They included different trials and reach very different effect sizes.

The real environmental footprint of these powders cannot be quantified from the available data. The most recent life cycle assessment, published in Foods in 2026, reaches a net negative carbon balance for a spirulina-derived colourant, but only with geothermally powered cultivation in Iceland and a soil carbon sequestration credit. Without both conditions the result does not transfer. Drying remains the dominant step, and it runs on electricity.

These reference points obviously do not replace medical advice, particularly in case of anaemia, pregnancy or ongoing treatment.

Frequently asked questions

Does Swiss spirulina really exist? Swiss production exists, in heated closed ponds or photobioreactors. What does not exist is spirulina harvested from a Swiss lake: the species needs warm alkaline water that does not occur naturally here.

How much spirulina per day? Clinical trials use 3 g and above, over at least twelve weeks. For culinary use, one or two teaspoons is plenty, and ANSES sees no risk below a few grams a day in adults, contamination risk aside.

Spirulina or chlorella? Spirulina is more digestible as it comes, better documented in clinical trials and less bitter. Chlorella supplies genuinely active vitamin B12, but in unpredictable amounts, and requires a cracked cell wall. Neither removes the need for a B12 supplement.

Does chlorophyll detoxify the body? That claim, found in many texts, rests on no usable human data. Chlorophyll is a pigment, not a treatment.

Does spirulina provide omega-3? Very little, and not the useful kind. Its 2.08 g of polyunsaturated fat per 100 g is mostly linoleic and gamma-linolenic acid, not EPA or DHA. For those, you want marine microalgae oils, a subject covered in choosing algae-based omega-3 supplements.

Can it go into bread? Yes, up to 3 % of flour weight. Beyond that the gluten network degrades and the dough loses stability.

Why does my powder smell of fish? That usually signals lipid oxidation, caused by storage in light, in heat or in a poorly sealed container. Sound powder smells of cut grass, not of low tide.