Unicellular seaweed rich in proteins (45%), fats (20%), carbohydrates (20%), fibre (5%), minerals and vitamins.Although proposed around 1940 as an important source of food for humanity, due to the difficulties and high cost of its cultivation, it is currently used as a dietary supplement and as a biofuel. The consumption of chlorella supplements during pregnancy causes the levels of carotenoids - lutein, zeaxanthin and β-carotene - to be doubled in breast milk (Nagayama 2014), and the concentration of dioxins to decrease and that of immunoglobulin A, IgA to increase (Nakano 2007). Research into its supposed properties (Panahi 2016) in relation to multiple aspects of health (lipid-lowering, hypoglycaemic, anti-oxidant, anti-cancer, liver protector, anti-hypertensive, immunity enhancer, anti-depressant, useful in the treatment of chronic obstructive pulmonary disease, fibromyalgia, ulcerative colitis...) is promising, but for now the scientific evidence is insufficient and needs to be confirmed (Noguchi 2014, American Cancer Society 2011, Halperin 2003, Merchant 2001). It must be ensured that it comes from a reliable source and there are quality controls to avoid contamination with heavy metals (arsenic, cadmium, copper, chromium, lead) and liver toxins such as microcystins (Desideri 2016, Kumar 2013, Heussner 2012). Dietary supplements of algae such as spirulina or chlorella are the food group with the highest concentration of arsenic (EFSA 2014). There have been reports of psychosis possibly induced by the abuse of chlorella alone or associated with other alternative dietary supplements (Yadav 2016, Selvaraj 2013). Moderate consumption from reliable sources would be low risk during breastfeeding, although it is absolutely non-essential.