Imagine a day scientists discover that foods you like are more nutritious than those you don't.

That day occurred more than 25 years ago. A series of experiments run by researchers in Sweden and Thailand showed that people absorb more iron from meals that appeal to them than from meals they find less appetizing. Promoters of good nutrition throughout much of the world appear to have taken note. Britain's number-one guideline, ahead of admonitions to eat more fiber and less fat, is simply: ''Enjoy your food." Norway, in its own set of guidelines, reminds its citizens that ''food and joy equal health," while Vietnam counsels people to have food ''that is delicious . . . and served with affection." In stark contrast, the latest edition of the US Dietary Guidelines, released last month, make no allusion that nutrition and taking pleasure in eating have anything to do with each other. Some believe it may be that very disconnection that is contributing to Americans' less-than-optimal diets, not to mention obesity. Part of the problem occurs on a gut level -- literally. In the late 1970s, Swedish and Thai researchers collaborated on a study that centered on a Thai meal of rice and vegetables spiked with chili paste, fish sauce, and coconut cream. They fed the meal to a group of Thai women and a group of Swedish women. The Thai women absorbed almost 50 percent more of the dish's iron than the Swedes, who ''liked the meal" up to a point, reported the researchers, ''but considered it very spicy."