This is a multicenter, unblinded, randomized study. The aim of this study is to research whether preoperative and postoperative oral nutritional supplement (ONS) (Resource 2.5 Compact/fibre compact) used at least 2 weeks prior the surgery and 10 days after surgery can improve the nutritional status of a colon cancer patient and reduce number of complications. The aim is also to investigate whether the oral nutritional support can shorten the hospital stay and improve the patients´ quality of life. The aim is also to find out whether the oral nutritional support can reduce 90-day mortality and improve disease free and overall survival. Consecutive patients diagnosed with primary adenocarcinoma of the colon who are considered for radical surgical procedure are enrolled in this study provided that the inclusion criteria are filled. Patients in the intervention group start oral nutritional support (ONS)2 portions a day for about 2 weeks prior to the operation starting at the time of randomization and continue ONS 10 days after the operation. Control group will continue with their regular diet without ONS until the operation. Both groups keep a food diary for 4 days right after the randomization and both one month and three months after the operation to assess the energy and nutrient intakes. Laboratory markers, NRS 2002, quality of life questionnaire, exercise questionnaire, bioelectrical impedance analysis (BIA) and handgrip strength as well as body composition on computer tomography scan are assessed prior to any treatment or supplement in order to estimate the patients' well-being and nutritional status prior to surgical operation. Laboratory parameters and QoL questionnaire are repeated right before the operation on admission to hospital as well as about 30 and 90 days after the operation in addition to BIA, handgrip strength to assess the effect of nutritional support. Data on complications, infections, length of stay in the hospital and mortality are collected. Another arm in this research is to discover more information on biological markers in colon cancer and cancer related malnutrition thus providing targets for future treatment and prognostic predictors. Tissue samples are collected during this research at the surgery.