Little is known about nutritional intake after discharge though it takes months to regain preoperative weight after gastrointestinal surgery. We studied whether a 4-mo intervention with dietary advice and protein-rich supplements would increase nutritional intake and gain in lean body mass (LBM) in patients who had undergone gastrointestinal surgery. Patients admitted for gastrointestinal surgery were randomized at discharge to serve as control patients (n = 47) or to receive intervention (n = 40). One month after discharge, the control patients had a nutritional intake (3-d diet record) comparable with the intake of the general population that did not increase further. During the 4 m, the intervention patients had an increased intake of protein (+22%) and energy (+16%), and an enhanced gain of LBM after 2 mo (control 0.8 kg versus intervention 2.1 kg; P = 0.009). After the 4-mo intervention, both LBM and fat were gained (control 1.7 kg LBM and 0.2 kg fat versus intervention 3.1 kg LBM and 1.5 kg fat; LBM: P = 0.029 and fat: P = 0.056). At discharge patients should increase protein intake to 1.5 g.kg-1.d-1 for 2 mo, e.g., by taking protein-rich liquid supplements.