Japanese has tons of words and phrases imported from other languages; these are called 外来語 がいらいご (gairaigo). But when words get imported, the meaning often changes quite a lot from the original.
Take ダイエット - diet, which in English means a food regimen, usually for weight loss. But in Japan ダイエット means anything related to weight loss, at all. So that includes everything from getting massages to reduce cellulite, to fad diets like the currently popular Morning Banana Diet, to exercise systems like Billy Banks' Tae Bo, a craze for which swept the country last year. A more traditional way of describing these things may be more accurate - 痩身法 そうしんほう soushinhou, which literally means 'slim body methods'.
One weird ダイエット method that has remained popular for white a time even though it sounds pretty fishy scientifically is 骨盤矯正 こつばんきょうせい kotsuban kyousei, which means 'pelvic bone correction'. Women in particular are supposed to do various exercises to correct and tighten up the pelvic bones so that they turn inward. This is supposed to change your body to one that is slim naturally, as well as cure constipation, irregular periods, and bad skin conditions! Also, the 'western way' of walking with the toes turned outwards, as opposed to the 'traditional Japanese way' of walking with the toes turned inwards, is supposed to encourage weight gain, thus explaining all those toes-turned outward, waddling 'fat Americans'. I don't know how this theory explains the ultra-thinness of ballet dancers who must be able to point their toes totally outwards though.