Chlorella is a genus of single-celled green algae belonging to the phylum Chlorophyta. It is spherical, measuring between 2 and 10 μm in diameter. Chlorella contains chlorophyll in its chloroplast. Through photosynthesis it multiplies rapidly requiring only carbon dioxide, water, sunlight, and a small amount of minerals to reproduce.

It was once widely believed that Chlorella should serve as our main source of food and energy because of its highly efficient photosynthetic apparatus. When dried, it is about 45% protein, 20% fat, 20% carbohydrate, 5% fiber, and 10% vitamins and minerals. A Chlorella diet would supply all the essential amino acids. Thus it is a complete protein. However, later studies proved that Chlorella loses most of its nutritional value when altered or processed in any way.

Under certain growing conditions, Chlorella yields oils high in polyunsaturated fats -Chlorella minutissima has yielded EPA at 39.9% of total lipids.

Clinical studies on Chlorella suggest effects including: dioxin detoxification, healing from radiation exposure, reduction of high blood pressure, lower serum cholesterol levels, accelerated wound healing, and enhanced immune function. Chlorella has also been found to have anti-tumor properties when fed to mice. Another study found enhanced vascular function in hypertensive rats given oral doses of chlorella. In 1961 Melvin Calvin, a Nobel Prize laureate, used Chlorella for his research on the pathways of carbon dioxide assimilation.