Abstract： Fat and fat-free mass (FFM) comprise the weight. Lean body mass, which describes the skeletal muscle and differs from the FFM, relates colsely to the metabolism. Weight is commonly used to present the dynamic balance of enegy intake and waste. Weight loss is very common in patients with various diseases, which can be classified as active loss and passive loss. Active loss of weight is often seen in fasting or food control in obese or overweight patients. Stress, infection, trauma, cancer are reasons for passive weight loss, including loss of both fat and fat-free mass. The time-speed and amount of weight loss are usually used to evaluate the nutrtional risk and malnutrition status. However, malnutrition is a more comprehensive index to predict the prognosis of patient. Weight loss, especially the lean body mass loss is related with nutritional metabolism, quality of life and clinical outcomes. It is urgent for medical staffs to diagnose and treat weight loss as soon as they find out.The Five-step approach for treating malnutrition may have effect on treating weight loss. Nutrition education, enteral and parenteral can promote weight gain on patiens. Whey protein, N-3 Polyunsaturated, leucine, and L- carnitine can reduce the loss of lean body tissue.
