Spirulina is sometimes touted as a superfood -- one with superior nutritional value and disease-fighting properties. And a September 2014 article in "The Guardian" noted that people in developing countries can use it as an inexpensive protein and micronutrient source to help fight malnutrition. You can't live on spirulina alone, however. You still need to follow a balanced and healthy diet to get all of the nutrients necessary for good health.
A 100-gram serving of raw spirulina has just 26 calories. In comparison, a cup of dried spirulina, or 112 grams, has 325 calories. You'd have to eat more than 6 cups of dried spirulina to provide enough calories for the day if you follow a 2,000-calorie diet. This would be essentially impossible for most people to do and quite a boring diet to follow overall.
Nutrients Lacking in Spirulina
Although spirulina is an excellent source of some nutrients, it doesn't provide all of the essential nutrients. For example, it doesn't contain vitamins B-12 or D. Even eating 6 cups of dried spirulina also wouldn't provide 100 percent of the recommended daily value for vitamin A, calcium, phosphorus, zinc, selenium or fiber. You need vitamin D, phosphorus and calcium for strong bones, vitamin A for proper vision and zinc for a healthy immune system. Fiber helps prevent constipation, selenium is important for forming DNA and vitamin B-12 is necessary for forming red blood cells.
Potential Overdose Risk
If you only ate spirulina and ate 6 cups per day, you could also put yourself at risk for possible overdoses of certain nutrients. These include niacin, iron, magnesium, sodium, copper and manganese. Niacin toxicity can cause headaches, itchiness, stomach problems, liver damage, diabetes, ulcers, erectile dysfunction and gout. Iron toxicity can cause liver problems, diabetes and skin pigmentation. Manganese toxicity can cause neurological problems, copper toxicity can cause Wilson disease and too much sodium can cause high blood pressure and increase your risk for a heart attack.
Spirulina may interact with medications meant to suppress your immune system. People with phenylketonuria, rheumatoid arthritis, multiple sclerosis and lupus shouldn't take spirulina because it could make these conditions worse, according to the University of Maryland Medical Center. Blue-green algae, such as spirulina, may also be contaminated with heavy metals, a toxic substance called anatoxin or toxic substances called microcystins. Because of this, it isn't recommended to eat more than 50 grams of spirulina per day, according to the New York University Langone Medical Center.