 After the nutritional assessment, both well nourished and undernourished patients will be instructed to consume an enteral drink, orally or by gastrostomy or enteral feeding tube, during 7 days before surgery. Seventy patients will receive 1 lt per day of a standard polymeric formula Fresubin 22, which gives 1000 Kcal and 35 g protein, does not contain free aminoacid nor omega fatty acids, and contains glutamine and arginine concentrations of milk proteins. In order to increase protein intake, 50 g día of Proteinex R will be added in this group. The other 70 patients will be instructed to consume 600 ml of the special immune-enhancing formula plus 20 g glutamine Supportan R Glutamine plus R , which contain 900 Kcal and 60 g proteinday, with 24.4 g glutamine, 2,2 g arginine and 4.4 g of omega 3 fatty acids, in a lower volume due to its higher energy density. Both products are enriched with essential vitamins and minerals. The enteral formulas will be assigned through randomized computer-generated numbers, in an open way. Patients that do not agree to participate, do not have enough time before the operation, do not tolerate the product and drink less than 100 ccday will be considered control subjects. The enteral products will be sold to the patients directly at the oncologic clinic, both the same prize, and lower to marketing prizes, due to the participation of Fresenius-Kabi in the protocol. However if the patients does not have the means, will receive it for free. All patients will be instructed to maintain their previous diet, adding the enteral supplement, or completing their requirement by tube feeding with standard or specific formulations e.g. diabetic formulation. 