Hematopoietic stem cell transplantation carries nutrition-related risks. Therefore, nutritional therapy needs to be initiated before transplantation even takes place. We assessed nutritional risk among patients who underwent allogeneic stem cell transplantation. We assessed nutrient supply (calorie supply and protein supply) by chart review. Assessments were made from the pretreatment phase of transplantation to after the end of parenteral nutrition in 51 patients who underwent allogeneic stem cell transplantation at Shizuoka Cancer Center between 2007 and 2012. We compared nutrition-related adverse events and parameters between two groups: those in whom % loss of body weight was >= 7.5 and those in whom % loss of body weight was < 7.5. A correlation was observed between changes in weight and skeletal muscle mass (r = 0.89; P= 7.5 group and the % loss of body weight < 7.5 group in the following variables: % loss of body weight, nutrient supply from calories and protein; orally ingested nutrient supply from calories and protein; start day of oral intake; and acute graft-versus-host disease. Orally ingested calories were negatively correlated with nutrition-related adverse events in both groups. Early and customized nutritional intervention may be optimal for all patients who undergo allogeneic stem cell transplantation to ameliorate body weight loss associated with nutrition-related adverse events.