Evolution and quality of the diet of women with severe and morbid obesity undergoing gastric bypass. The objective of this study was to evaluate the changes of dietary intake and quality of the diet in patients undergoing gastric bypass. In forty-four women with severe and morbid obesity it was assessed their nutrient intakes before and 6, 12, and 18 months after gastric bypass by using three-day food records. Vitamin and mineral intakes from supplements were strictly controlled though personalized records. With the exceptions of calcium and vitamin A, energy and nutrient intakes were significantly decreased at 6, 12, and 18 month after bypass compared to the pre-surgery period. Dietary intakes of calcium, iron, zinc, copper, folic acid, vitamin C, and vitamin E were below 100% of adequacy from the 6th month after the surgery and thereafter. This situation is reverted when nutrient intakes supplied by supplements are taken into account. Although a "U" shape trend was observed in the nutrient intakes results during the experimental period, in most cases the differences between the observed values at month 12 and 18 were not significant. In conclusion, these patients had important reductions of their energy and nutrient intakes as result of gastric bypass. Routine supplements may correct this situation, nevertheless, the anatomical alterations inherent to this type of surgery may cause that total nutrient intakes reaching adequacy values slightly above 100%, may not necessarily be able to avoid the development of nutritional deficiencies.