Introduction Due to frequent treatment side effects and weight loss, colorectal cancer patients require oncologic care and nutritional counseling both during and after hospitalization. The current study evaluated differences in discharge and side effects management and nutritional behavior between colorectal cancer patients of a control group without systematic counseling and of an intervention group with access to structured in- and outpatient oncology nurse and nutritional counseling. Methods The presented explorative, quantitative, single-center, interventional pilot study is a health services research project with a quasi-experimental design. Using a self-designed standardized questionnaire, data were collected from the control group (n = 75) before and from the intervention group (n = 114) after the introduction of in- and outpatient oncology nurse and structured systematic nutritional counseling. The in- and outpatient counseling services were developed and evaluated in the form of a structured nurse-led counseling concept. Results Intervention group patients profited significantly from inpatient oncology nurse counseling in seven different areas of discharge management. No differences were observed concerning patient-reported general and gastrointestinal side effects except for xerostomia and dysphagia, but of the patients participating in both in- and outpatient oncology nurse counseling, 90.0% were better able to cope with general side effects of treatment. Patients with in- and outpatient structured systematic nutritional counseling more frequently received nutritional information (p = 0.001), were better at gauging food intolerances (p = 0.023), and followed the dietician's advice in cases of gastrointestinal side effects significantly more often (p = 0.003) than control patients. Counselor-reported outcomes concerning gastrointestinal side effects showed improvement in most of the patients taking part in systematic in- and outpatient nutritional counseling, except for weight loss in 4 patients. Conclusion In- and outpatient counseling in discharge and side effects management and nutrition improve the outcomes of colorectal cancer patients. Outpatient counseling should be further developed and evaluated in future studies.