Blue-Green Algae for Weight Control

Some dieters say that blue-green algae helps satisfy appetite and supplies good nutrition while dieting.

Blue-green algae (spirulina) is a concentrated source of nutrients compared to most foods, but it is expensive compared to other supplemental sources of protein, vitamins, and minerals. Research is limited, but nonetheless has found little benefit of spirulina to dieters.

Blue-green algae is a rich source of protein, vitamins, minerals, and essential fatty acids. In one double-blind trial, overweight people who took 2.8 grams of blue-green algae as spirulina three times per day for four weeks experienced only small and statistically nonsignificant weight loss.¹ Thus, although spirulina has been promoted as a weight-loss aid, the current scientific evidence supporting its use for this purpose is weak.

Few side effects have been reported from the ingestion of blue-green algae. However, as blue-green algae can accumulate heavy metals from contaminated water, consuming blue-green algae could increase the body’s load of lead, mercury, and cadmium,² though noncontaminated blue-green algae have been identified.³ Another popular species of blue-green algae, Aphanizomenon flos-aquae, has been found to produce toxins.⁴ A few reports also describe allergic reactions to blue-green algae. Animal studies have found spirulina to be safe during pregnancy.^{5, 6, 7}

There is one case report of a man who developed liver damage while taking spirulina.⁸ As he was also talking three prescription medications, it is not clear whether the spirulina caused or contributed to the liver injury.

Blue-green algae grow in some lakes, particularly those rich in salts, in Central and South America, and Africa. They are also grown in outdoor tanks specifically to be harvested for nutritional supplements.