Our good friend Spirulina?

As promised, here is some news about Spirulina.

Spirulina is a biomass of cyanobacteria (blue-green algae) which can be consumed by humans and animals, and which yields a food supplement much valued by athletes. Commercially, Spirulina is booming : in China, production took a 226% leap in 7 years, reaching 62’300 tons in 2010, according to the FAO, and its growth rate leads experts to predict a 651 million dollar market in 5 or 6 years.
In France, and more recently in Switzerland, several firms have started to grow Spirulina, relying on proximity, biological production and nutritional properties to catch the attention of health-conscious customers.

Nutritional composition: content is relative!

Spirulina certainly looks very attractive. A summary of its fantastic nutrient density is given by my colleague Nicolas Aubineau on his website : Spirulina is not only rich in protein and iron, it also provides good fatty acids, vitamins, magnesium and other micronutrients. Doesn’t that look perfect? However, my colleague Leila Sahinpasic , long fascinated by the nutritional properties of algae, reminds us that the exact composition depends on the different species and their growing conditions, and is highly variable. It’s rather like meat: the nutritional value of any particular piece of meat depends on what the animal ate during its life.

Spirulina may look perfect, but her riches are very relative. Her protein content looks huge because it is given in relation to the total dry weight: 60 g of protein for 100 g of dry Spirulina extract. That’s a lot. But 100 g of dry Spirulina extract is also a lot. Spirulina flakes are often sold in packages of 50 or 100 g. This means that to consume 20 g of protein, equivalent to two eggs, you would have to eat over one third of a package of Spirulina which costs CHF 45.- (or CHF 15.- per portion of protein!). The usual recommended daily portion of Spirulina is about 5 to 10 g, or about… 3 to 6 grams of protein.

The iron in Spirulina may not have the expected effect

Spirulina’s other great selling point is its iron content. On line shops claim that it is particularly recommended for people with an iron deficiency, and that it helps combat fatigue, specifically in athletes. Certainly, few foods can rival an iron content of 10 mg of iron per 100 g of product! Some, such as “boudin noir” (French blood sausage) contains up 22 mg/100 g. Dried meat has about 10 mg/100 g. Cooked lentils, pasta or spinach contain only about 2 to 3 mg of iron per 100 g.

To investigate whether Spirulina has any real effect on physical performance and on fatigue, two of my former students, Christelle Ducrest et Elodie Bapst, have worked through (almost) the entire published scientific literature on this subject for their Bachelor thesis in Nutrition and dietetics at the School of Health professions of Geneva.

The first notable fact is the lack of good studies. Several start out well: participants are randomised into two groups, one group being given Spirulina and the other a placebo. The problem is that afterwards, when interpreting the results, many investigators compared the results before and after the participant takes the product. Methodologically, this is nonsense, since it makes it impossible to ascertain that the observed effect is due to the studied product.

In the end, only five studies on human subjects turned out to be of sufficient quality. Only one of these investigated the plasmatic iron concentration (but not in athletes, worse luck). And there – wow. We had to pinch ourselves several times, the results were so unexpected: in the group receiving the Spirulina supplement, plasmatic iron concentration actually dropped! In the placebo group, it did not (Suliburska et al. 2016).

The other studies attempted to show an effect on physical performance, particularly in athletes. One of them showed a slightly better performance in 9 men, all trained runners, who were asked to run on an exerciser for 2 hours at 70-75% of their Vo2max, then at 95% of their VO2max until exhausted; in this last part, the subjects who had received the Spirulina kept on for 40 seconds longer than the subjects who had not (Kalafati et al. 2010). Nice, of course, but hardly spectacular.

Another study had a larger number of subjects: 52, all men of sedentary habits and overweight. Here also the Spirulina supplement correlated with an improvement in performance, but as the authors give no figures in their publication, there is way to guess the seize of the effect (Hernandez-Lepe et al. 2019). The other publications (Franca et al. 2010; Lu et al. 2006) show no direct effect on either performance or fatigue.

The baby and the bath water

It would be easy to conclude that Spirulina is no use.

I would not say that. What I would say is that current knowledge is insufficient and therefore we should be cautious. I would not recommend Spirulina to someone with an iron deficiency, or only with frequent monitoring to make sure of the effect (but that seems demanding and expensive). Neither would I recommend it as a protein supplement, there are less expensive ways to achieve that.

Beyond that, though the studies are insufficient to say with any certainty that Spirulina improves performance or combats fatigue, they are equally insufficient to say that it is useless.

As so often in nutrition science, there is a lack of well-conducted studies, of studies on women, of studies that take into account other parameters that may influence performance or fatigue.

And as so often in nutrition science, scientific support of the selling points is weak.