We sought to determine if an increased oral intake with a noninvasive nutrition program in patients with cystic fibrosis could influence growth, weight gain, and pulmonary function. Thirty-seven patients, aged 2 to 27 years, were instructed to consume a nonrestricted fat diet during an intervention period of 4 years. The results showed that patients increased the mean energy intake significantly to a level of more than 120% of the recommended daily allowance. The enhanced intake resulted in significant weight gain. Pulmonary function (forced expiratory flow 25%-75%) deteriorated during the 2-year preintervention period but stabilized during the 4-year intervention period. Both male and female patients were able to maintain their established height and weight scores during adolescence. The recommendation for a high-energy diet with no restrictions placed on the fat intake and the control of the steatorrhea by administration of an optimal enzyme dosage is supported by our data. Individualized nutritional counseling should be attempted before implementing invasive nutritional intervention programs.