Provided is an agent which can suppress or prevent decrease in muscle in malnutrition or potential malnutrition in a dialysis patient, etc. by reducing catabolism or promoting assimilation of proteins in the human body. An agent for reducing catabolism or promoting assimilation of proteins, the agent comprising protein in an amount of 0.5 to 5g, phosphorus in an amount of 10 to 50 mg, sodium in an amount of 10 to 100 mg, and potassium in an amount of 5 to 50 mg per 100 kcal of energy. The agent may further comprise lipids, carbohydrates, minerals and water, and may be ingested as liquid food. In this case, the amount of lipids is 1 to 5 g and the amount of carbohydrates is 10 to 20 g per 100 kcal of energy, and the energy per 1 ml is 1 to 2 kcal.
