This study was undertaken to test the hypothesis that a change in the mother's diet at the time of birth and continued during suckling modifies the intestinal transport of nutrients in the suckling offspring. Pregnant rat dams were fed one of four semisynthetic diets during pregnancy [high or low n-6/n-3 diet or a diet enriched with arachidonic acid (AA) or docosahexaenoic acid (DHA)] and were fed the same diet at the time of birth or switched to another diet. The greatest body weight gain was in the suckling rats (15-16 days of age) fed a low n-6/n-3 diet. Switching from this diet caused weight loss, and the observed weight gain with the low n-6/n-3 diet was prevented by previous exposure of the mother to the high n-6/n-3 diet or the AA- or DHA-containing diet. Although continuous feeding of a high n-6/n-3 diet to the mother during pregnancy and lactation was associated with the lowest in vitro rates of fructose uptake, switching the mother to another diet during lactation did not necessarily correct the low absorption. In contrast, continuous feeding of a high n-6/n-3 diet to the mother during pregnancy and lactation is associated with the highest maximal transport rate of glucose uptake into the jejunum and ileum. Jejunal uptake of fatty acids 12:0, 18:0, 18:3(n-3), and cholesterol was less with the low n-6/n-3 diet compared with the high n-6/n-3 diet, whereas the ileal uptake of 18:0 and 18:3(n-3) was higher with the low n-6/n-3 diet. Thus the ontogeny of the intestine is critically influenced by the mother's diet during gestation as well as during the nursing period. Some of the diet-associated changes in nutrient uptake resulting from the mother's diet during pregnancy could be corrected by dietary interventions introduced after birth.