Current health guidance says that no one should eat more than four portions of oily fish a week. Pregnant women and those breastfeeding are advised to eat no more than two portions a week as are all girls who might bear a child in the future. However, all of us are encouraged to eat at least two portions of fish a week, at least one of which should be an oily fish. So-called oily fishes include mackerel, salmon, pilchards and sardines. The positive aspects of oily fish are that they contain important essential fatty acids that are thought to be highly beneficial to health. The advice against eating too much oily fish is based on concerns about high levels of the pollutants known as PCBs and dioxins in the flesh of such fish. However, government health advisors stress that most British people eat nowhere near enough fish and are anxious not to put out negative messages about oily fish.