Involuntary weight loss is often seen among patients with gastrointestinal (GI) cancer. Weight loss may influence quality of life (QoL) and is a predictor of survival. The present study is an attempt to improve body weight development in GI cancer patients by individual support (IS), including nutritional measures. Patients were randomized in a 2 x 2 design between 1) IS, including nutritional support, 2) group rehabilitation (GR), 3) IS + GR (ISGR), or 4) standard care (SC). Data concerning dietary intake (24-h recalls), body weight, and QoL (EORTC-QLQ C-30) were collected over 2 yr for 67 patients with colorectal or gastric cancer, randomized to IS or ISGR. Data on weight and QoL were collected for 70 patients with the same diagnoses randomized to GR or SC. Despite a tendency to greater weight loss at inclusion, the IS + ISGR group managed to gain weight significantly more rapidly and to a greater extent than the GR + SC group. The differences became statistically significant at 12 and 24 mo (P < 0.05). Patients with weight loss at baseline increased their energy intake and weight more than those without weight loss. No differences were seen in QoL ratings between randomization groups, but there was a positive correlation between weight development and QoL and a negative correlation between fatigue and weight development. There was a numerical difference, not statistically significant (P = 0.3), indicating a shorter time of survival in patients in the GR + SC group. IS, including nutritional support, leads to more rapid weight gain than SC in patients with newly diagnosed GI cancer.