Undernutrition① is a condition in which there is not enough food energy as measured in calories or kilo joules②. Undernutrition usually means that not enough total food is consumed. The main characteristics are loss of body weight and wasting of body fat and later muscle. Undernutrition may due to a failure of the food supply or to deliberate③ fasting， or it may be secondary to prolonged disease.
Malnutrition covers at least 25 different deficiency④ diseases resulting from lack of one of the essential nutrients： protein， vitamins， essential fats， or nutrient elements. Rickets and iron-deficiency anemia⑤ are examples of the result of malnutrition. Multiple deficiencies are more likely than single， though one type often predominates. The deficiency disorder may be subclinical⑥ and not show characteristic features.
The most common severe form of protein energy malnutrition， nutritional marasmus⑦ usually occurs in the first year of life. The affected child is extremely underweight and has lost all subcutaneous fat. The body is wizened， the face gaunt， and the limbs like matchsticks. The cause is a diet very low in calories from all sources (including protein)， often from early weaning to bottled formula diluted because of poverty.
① undernutritionn. 营养不足
② joulesn. 焦耳
③ deliberateadj. 深思熟虑的，慎重的，谨慎的； 故意的；不慌不忙的
④ deficiencyn. 不足，缺乏；缺陷，缺点
⑤ anemian. 【医】贫血(症)
⑥ subclinicaladj. 轻度不正常的；无临床症状的
⑦ marasmusn. 消瘦；消瘦症
营养不良
营养不良指不能摄入以卡路里或千焦耳为单位测量的足够的食物能量。它常常指没有吃够总共所需的食物，主要特点是体重下降和过度消耗体内脂肪乃至肌肉。营养不良主要是由食物供应不足，故意节食或长期患病所至。
营养失调至少包括25种由于缺乏人体必需的某一种营养元素(如蛋白质、维生素、基本的脂肪或其他营养元素)而导致的不同疾病。佝偻病和缺铁性贫血就是营养失调的例子。尽管患者可能某种症状特别明显，其实他也许缺乏多种营养素。营养不足可能不算临床疾病，而且没有典型的特征。
最为严重的蛋白质能量营养不足和营养性消瘦常常发生在一周岁的患者身上，患病的小孩子体重极轻，几乎丧失了所有的皮下脂肪，身体消瘦，脸庞憔悴，四肢就像火柴棒一样。患病原因是饮食中包括蛋白质在内的各种营养元素和卡路里的含量都太低了，这常常是因为贫穷，不得不过早断奶用稀薄奶粉喂养造成的。
