营养不良

　　Malnutrition results from imbalance between the body's needs and the intake of nutrients, which can lead to syndromes of deficiency, dependency, toxicity, or obesity. Malnutrition includes undernutrition, in which nutrients are undersupplied, and overnutrition, in which nutrients are oversupplied. Undernutrition can result from inadequate intake; malabsorption; abnormal systemic loss of nutrients due to diarrhea, hemorrhage, renal failure, or excessive sweating; infection; or addiction to drugs. Overnutrition can result from overeating; insufficient exercise; overprescription of therapeutic diets, including parenteral nutrition; excess intake of vitamins, particularly pyridoxine (vitamin B6), niacin, and vitamins A and D; and excess intake of trace minerals.

　　营养不良由机体需要与营养素摄入之间不平衡所致，可引起缺乏、依赖、中毒或肥胖等症。营养不良包括营养低下，即营养素供给不足，和营养过剩，即营养素供给过度。营养低下可由摄入不足、吸收不良、腹泻、出血、肾衰或过度出汗而至营养素丢失、感染和吸毒等引起。营养过剩可由摄食过度、缺少锻炼、治疗膳食摄入过度（包括胃肠外营养）、过量摄入维生素，尤其是吡哆醇(维生素B6 )、尼克酸和维生素A和D、以及微量元素摄入过多所致。

　　Malnutrition (undernutrition and overnutrition) develops in stages, which usually require considerable time. First, nutrient levels in blood and/or tissues change, followed by intracellular changes in biochemical functions and structure. Ultimately, symptoms and signs appear; morbidity and mortality can result.

　　营养不良(营养低下和营养过剩)的发展是有阶段的，通常需要相当长的时间。首先，血液和/或组织中营养素水平改变，然后是生化功能和结构发生改变，最终出现症状和体征，导致发病和死亡。

　　Early Detection

　　早期发现

　　The key to early detection is awareness that persons in certain circumstances have a high risk of undernutrition or overnutrition. Undernutrition is associated with poverty and social deprivation, occurring among the poor, including some immigrants arriving from developing countries. The risk of undernutrition is also greater at certain times in a person's life, ie, infancy, early childhood, adolescence, pregnancy and lactation, and old age. Overnutrition is associated with a sedentary lifestyle and the continuous availability of food in more affluent countries.

　　Persons in the following circumstances may be at risk of malnutrition.

　　早期发现的关键是要认识到，有些人是营养低下或营养过剩的高危人群。营养低下与贫穷和物质匮乏有关，通常发生于穷人中，如来自发展中国家的移民。人一生中的某些阶段患营养低下的危险性也很高，如婴儿期、幼儿期、青少年期、妊娠哺乳期、以及老年期。营养过剩则与久坐习惯及富裕国家中食物丰富有关。

　　下列情况人群就有发生营养不良的危险。

　　Infancy and childhood: Because of the high demand for energy and essential nutrients, infants and children are at particular risk of undernutrition. Protein-energy malnutrition in children consuming inadequate amounts of protein, calories, and other nutrients is a particularly severe form of undernutrition that retards growth and development. Hemorrhagic disease of the newborn, a life-threatening disorder, is due to inadequate vitamin K. Deficiencies of iron, folic acid, vitamin C, copper, zinc, and vitamin A may occur in inadequately fed infants and children. In adolescence, nutritional requirements increase because the growth rate increases. Anorexia nervosa, a form of starvation, may affect adolescent girls.

　　婴儿和儿童 婴儿和儿童对能量和必需营养素的需要量高，其营养低下的危险性也高。儿童因蛋白质、热量和其他营养素摄入量不足造成的蛋白质-能量型营养不良是一种尤为严重的营养不良，它会延缓儿童的生长和发育。新生儿出血性疾病可以危及生命，它是由维生素K摄入不足所致。婴儿及儿童喂养不当也会造成铁、酸、维生素C、铜、锌和维生素A等的不足。因生长加快，青少年对营养的需要增高。神经性厌食症是饥饿的一种形式，它对少女有影响。

　　Pregnancy and lactation: Requirements for all nutrients are increased during pregnancy and lactation. Aberrations of diet, including pica (the consumption of nonnutritive substances, such as clay and charcoal), are common in pregnancy. Anemia due to folic acid deficiency is common in pregnant women, especially those who have taken oral contraceptives. Folic acid supplements are now recommended for pregnant women to prevent neural tube defects (spina bifida) in their children. An exclusively breastfed infant can develop vitamin B12 deficiency if the mother is a vegan. An alcoholic mother may have a handicapped and stunted child with fetal alcohol syndrome, which is due to the effects of ethanol and malnutrition on fetal development.

　　妊娠和哺乳 在妊娠期和哺乳期，所有营养素的需要量都增高。饮食失常在孕期常见，如异食癖(食非营养性物质如粘土和木炭)。因叶酸缺乏而引起的贫血在孕妇中也很常见同，尤其是口服避孕药服用者。现在已建议孕妇补充叶酸以预防儿童出现神经管缺陷症(脊柱裂)。如果母亲是素食者，则完全母乳喂养的婴儿就可能发生维生素B12缺乏症。母亲酗酒时，儿童出生后可能因胎儿酒精中毒综合征造成残疾或侏儒症，其原因是酒精和营养不良影响胎儿发育。

　　Old age: A diminished sense of taste and smell, loneliness, physical and mental handicaps, immobility, and chronic illness can militate against adequate dietary intake in the elderly. Absorption is reduced, possibly contributing to iron deficiency, osteoporosis (also related to calcium deficiency), and osteomalacia due to lack of vitamin D and absence of exposure to sunshine.

　　With aging -- independent of disease or dietary deficiency -- there is progressive loss of lean body mass, amounting to about 10 kg in men and 5 kg in women. It accounts for the decrease in BMR, total body weight, skeletal mass, and height and for the increase in mean body fat (as a percentage of body weight) from about 20 to 30% in men and from 27 to 40% in women. These changes and a reduction in physical activity result in lower energy and protein requirements compared with those of younger adults.

　　老年人 味觉和嗅觉减退、孤独、身体与精神障碍、不活动以及慢性疾病都会影响上老年人摄入足够的食物。吸收功能减退，可能引起缺铁、骨质疏松症(也与钙不足有关)及缺乏维生素D缺乏和阳光照射所致的骨软化症。

　　除了疾病和饮食不足以外，人体肌肉组织也会随年龄老化而不断减少，男性可减少约10kg，女性5kg。这也是基础代谢率、总体重、骨骼体积和身高降低及平均体脂增高(按体重的百分比计)的原因，其中男性由20%增至30%，女性由27%增至40%。与中年相比，这些变化再加上身体活动减少就会引起能量和蛋白质需要量的减少。

　　Chronic disease: In patients with chronic disease, malabsorption states (including those resulting from surgery) tend to impair the absorption of fat-soluble vitamins, vitamin B12, calcium, and iron. Liver disease impairs the storage of vitamins A and B12 and interferes with the metabolism of protein and energy sources. Patients with kidney disease, including those on dialysis, are prone to develop deficiencies of protein, iron, and vitamin D. Some patients with cancer and many with AIDS have anorexia, which complicates treatment. In patients receiving long-term home parenteral nutrition--most commonly after total or near-total resection of the gut--vitamin and trace mineral deficiencies must be especially guarded against. A physician should ensure that biotin, vitamin K, selenium, molybdenum, manganese, and zinc are adequately supplied.

　　慢性疾病 慢性疾病患者吸收障碍(包括外科手术引起的吸收障碍)极易损害脂溶性维生素、维生素B12、钙和铁的吸收。肝脏疾病破坏维生素A和维生素B12的贮存，干扰蛋白质和能量物质的代谢。肾脏疾病患者，包括透析治疗者，容易出现蛋白质、铁和维生素D的缺乏。有些癌症患者和众多AIDS患者都有神经性厌食症，这使得治疗更加困难。在家进行长期胃肠外营养治疗的病人，通常为肠全切除或次全切除病人，应特别警惕维生素和微量元素缺乏。医生应确保生物素、维生素K、硒、钼、镁和锌的充足供给。

　　Vegetarian diets: The most common form of vegetarianism is ovo-lacto vegetarianism, in which meat and fish are eschewed but eggs and dairy products are eaten. Iron deficiency is the only risk. Ovo-lacto vegetarians tend to live longer and to develop fewer chronic disabling conditions than their meat-eating peers. However, their lifestyle usually includes regular exercise and abstention from alcohol and tobacco, which may contribute to their better health. Vegans consume no animal products and are susceptible to vitamin B12 deficiency. Yeast extracts and oriental-style fermented foods provide this vitamin. Intake of calcium, iron, and zinc also tends to be low. A fruitarian diet, which consists solely of fruit, is deficient in protein, salt, and many micronutrients and is not recommended.

　　素食 最常见的素食者是乳蛋素食者，即不吃肉和鱼而吃鸡蛋和乳制品。唯一的危险是缺铁。与食肉者想比，乳蛋素食者往往寿命更长，得慢性致残疾病也少。在日常生活中，他们经常锻炼，不沾烟酒，这也有助于他们的健康。素食者不吃任何动物性食物，易患维生素B12缺乏症。酵母精和东方式的发酵食物能提供这种维生素。但钙、铁和锌的摄入量往往很低。果蔬饮食是由水果组成的，缺乏蛋白质、盐和多种微量营养素，也不推荐使用。

　　Fad diets: Many commercial diets are claimed to enhance well-being or reduce weight. A physician should be alert to early evidence of nutrient deficiency or toxicity in patients adhering to them. Such diets have resulted in frank vitamin, mineral, and protein deficiency states and cardiac, renal, and metabolic disorders as well as some deaths. Very low calorie diets (= 1 quart of hard liquor per day lose weight and become undernourished. Drug addicts are usually emaciated. Alcoholism is the most common cause of thiamine deficiency in the USA and may lead to deficiencies of magnesium, zinc, and other vitamins.

　　酗酒或毒品依赖 众所周知，酗酒或吸毒病人的饮食习惯问答是不可靠的，因此，明智而审慎地向其亲友询问是必要的。成瘾导致生活方式紊乱，无视营养是否足够。营养素的吸收和代谢也受到损害。高度酒有毒，且能导致组织损伤，尤其是损伤胃肠道、肝脏、胰脏、脑和外周神经系统。啤酒饮用者由于不断饮用食物，会导致其体重增加。但每天白酒大于等于1L的嗜酒者体重会减轻，导致营养低下。吸毒上瘾的人通常憔悴消瘦。在美国，酒精中毒是导致硫胺素缺乏的最常见因素，现时也可以导致镁、锌和某些维生素的缺乏。

　　Diagnosis

　　诊断

　　The diagnosis of malnutrition is based on results of the medical and diet history, physical examination, and selected laboratory tests. Results are compared with norms of weight for height, body mass index (BMI), dietary intake, physical findings, and plasma levels of nutrients and nutrient-dependent substances, such as hemoglobin, thyroid hormones, transferrin, and albumin.

　　应根据病史和饮食史、体检及专门的实验室检查结果对营养不良作出诊断。并将诊断结果与身高体重正常值、体质指数(BMI)、摄入量、体检结果、血浆中营养素及营养素依赖性物质如血红蛋白、甲状腺激素、转铁蛋白和白蛋白的水平等进行比较。

　　History: A history of poor appetite, GI disturbance, and recent sizable weight loss suggests the possibility of malnutrition. A history of bleeding may indicate iron deficiency. Chronic use of alcohol, cocaine, heroin, immunosuppressants, or certain antibiotics and anticonvulsants raises questions about the adequacy of vitamin and mineral nutrition. A diet history may reveal food faddism, lack of variety, or inadequate or excessive intake of energy and essential nutrients.

　　病史 食欲差、胃肠道障碍及近期体重明显减低等病史均提示有营养不良可能。出血史表明缺铁。长期使用酒精、可卡因、海洛因、免疫抑制剂及抗惊厥剂会使维生素和矿物质是否充足成为问题。通过膳食史可以发现是否是时尚饮食、食物品种是否单一、能量和必需营养素摄入不足或过多等情况。

　　Physical examination: Significant changes in body composition and organ function may suggest malnutrition as a cause. The skin should be examined for dryness, scaliness, atrophy, petechiae, and ecchymoses, and the mouth for angular stomatitis, glossitis, swollen or bleeding gums, and decayed teeth. Depigmentation of the hair and spooned nails point to malnutrition. The musculature should be examined for size, strength, and tenderness. A neurologic examination may detect disorientation, an abnormal gait, altered reflexes, and sensory or motor neuron abnormalities. Painful bones and joints, osteopenia, and distortions in the shape or size of bones (eg, rachitic rosary) may indicate current or past malnutrition.

　　体格检查 体格和器官功能方面的显著改变可以提示营养不良因素。皮肤应检查有无干燥、鳞屑、增生、瘀点及瘀斑；口腔应检查有无口角炎、舌炎、肿胀、齿龈出血和龋齿。头发脱色和匙状甲表明营养不良。肌肉系统应检查其大小、强度及柔韧性。神经系统检查可发现定位异常、步态异常、反射改变及感觉或运动神经元异常。骨和关节痛疼、骨质减少及骨的形状或大小改变(如佝偻病性串珠)均表明目前或过去营养不良。

　　Anthropometric measurements are essential to diagnosis. Nutritional status can be classified on the basis of BMI. The triceps skinfold (TSF) estimates the amount of body fat within 20% and is therefore useful in determining the body's energy stores. Based on the midarm muscle area, an approximate measure of lean body mass, muscle mass may be classified as adequate, marginal, depleted, or wasted. form www.med66.com

　　人体测量数据对诊断是至关重要。营养状态可以根据BMI进行分类。三头肌皮褶厚度(TSF)可以估计20%之内的体脂，因此，在确定机体能量贮存方面很有用。根据上臂肌面积可大致确定瘦体重，如分为合适、临界、耗竭或消瘦几类。

　　Laboratory tests: A CBC and measurement of certain plasma proteins that reflect the adequacy of amino acid nutrition (albumin, prealbumin, and transferrin) aid in the diagnosis of malnutrition, as does measurement of plasma lipids and related lipoproteins. Abnormal electrolyte levels may point to a mineral deficiency or a defect in ion homeostasis. Fat- and water-soluble vitamins can be measured in plasma and urine. Skin tests using antigens are used to evaluate cell-mediated immunity. Various imaging techniques (x-ray, CT, and MRI) may be helpful.

　　实验室检查 全血细胞计数及反映氨基酸营养程度的某些蛋白质 (白蛋白、前白蛋白和转铁蛋白) 测定数据有助于营养不良的诊断。血浆脂类和相关的脂蛋白测定也有帮助。电解质异常可能表明矿物质缺乏或离子的内稳态受到破坏。脂溶性和水溶性维生素可在血浆和尿中测得。抗原皮试用于评估细胞免疫。各种影像技术(X线、CT和MRI)也有帮助。

　　Surgical procedures place additional stress on undernourished persons. Indicators of malnutrition have been used to develop a prognostic nutritional index (PNI), a linear predictive model of increased morbidity and mortality after surgical procedures. The formula for PNI uses serum albumin (A) in g/dL, TSF in mm, serum transferrin (TFN) in mg/dL, and delayed hypersensitivity (DH) response (0 to 2), measured by leukocyte migration inhibition, transformation, and cytotoxicity tests.

　　手术可增加营养低下者应激反应。营养不良的指标已被用于诊断营养预后指数(PNI)，这是对外科手术后发病率和死亡率增加的一种线性预后模式。血清白蛋白g/dl(A)、三头肌皮褶厚度mm(TSF)、血清运铁蛋白mg/dl(TFN)、以及用白细胞移动抑制、转化、细胞毒性试验检测的迟发性过敏反应(0~2)(DH)均用于PNI公式中：PNI%＝158-16.6(A)-0.78(TSF)-0.2(TFN)-5.8(DH)

　　For example, a well-nourished patient with A = 4.8, TSF = 14, TFN = 250, and DH = 2 has a PNI of 158.0 - 152.2, or a 5.8% chance of complications. A malnourished patient with abnormal indexes (A = 2.8, TSF = 9, TFN = 180, and DH = 1) has a PNI of 158 - 95.3, or a 62.7% chance of complications.

　　例如，一个营养良好的病人，A＝4.8，TSF＝14，TFN＝250，DH＝2，其PNI为158.0~152.2，或者说他患并发症的机会为5.8%。一个指标异常的营养不良病人(A＝2.8，TSF＝9，TFN＝180，DH＝1)，其PNI为158~95.3，或他患并发症的机会为62.7%。