Salmon is a popular food. Consuming salmon is considered to be reasonably healthy due to the fish's high protein, high Omega-3 fatty acids, and high vitamin D content. Salmon is also a source of cholesterol, ranging 23--214 mg/100g depending on the species. According to reports in the journal Science, however, farmed salmon may contain high levels of dioxins. PCB (polychlorinated biphenyl) levels may be up to eight times higher in farmed salmon than in wild salmon. Omega-3 content may also be lower than in wild caught individuals, and in a different proportion to what is found naturally. Omega 3 comes in three types, ALA, DHA and EPA; wild salmon has traditionally been an important source of DHA and EPA, which are important for brain function and structure, among other things.