Brite adipocytes are inducible energy-dissipating cells expressing UCP1 which appear within white adipose tissue of healthy adult individuals. Recruitment of these cells represents a potential strategy to fight obesity and associated diseases. Using human Multipotent Adipose-Derived Stem cells, able to convert into brite adipocytes, we show that arachidonic acid strongly inhibits brite adipocyte formation via a cyclooxygenase pathway leading to secretion of PGE2 and PGF2α. Both prostaglandins induce an oscillatory Ca(++) signaling coupled to ERK pathway and trigger a decrease in UCP1 expression and in oxygen consumption without altering mitochondriogenesis. In mice fed a standard diet supplemented with ω6 arachidonic acid, PGF2α and PGE2 amounts are increased in subcutaneous white adipose tissue and associated with a decrease in the recruitment of brite adipocytes. Our results suggest that dietary excess of ω6 polyunsaturated fatty acids present in Western diets, may also favor obesity by preventing the "browning" process to take place.