体重由脂肪和去脂体重组成。去脂体重与瘦体组织又有区别，后者描述机体的骨骼肌含量，与人体的代谢密 切相关。体重的稳定常用来评价能量摄入和丢失是否动态平衡。体重丢失在不同疾病的患者身上很常见，根据不同的原因 分为主动丢失和被动丢失，主动丢失大多出现在减重患者主动禁食或者控制食量等情况下，临床上常见的体重丢失大多为 应激、感染、创伤、肿瘤等引起的被动的混合型体重丢失。体重丢失的程度（速率和量）常被用来评估是否存在营养风险 和营养不良，但是体重丢失又区别于营养不良，后者是判断患者预后更为综合的评价指标。体重丢失特别是瘦体组织丢失 会影响患者的营养代谢、生存质量和临床治疗结局。体重丢失需要临床工作者早发现、早诊断、早治疗。营养不良的五阶 梯治疗可以被用来作为纠正患者体重丢失的治疗思路，通过营养教育、肠内营养联合肠外营养的升阶梯干预可以有效的恢 复患者体重。临床常用的营养组件如乳清蛋白、n-3 多不饱和脂肪酸、亮氨酸、L- 肉碱等特殊营养物质经动物实验和临床 研究证实对于瘦体组织的丢失有改善作用。

 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.