Malnutrition can be caused by overnutrition (excess energy or nutrient in-take) or undernutrition (deficient energy or nutrient intake). We usually think of malnutrition as a condition that results when the cells do not receive an adequate supply of the essential nutrients because of poor diet or poor utiliza-tion of food (Figure 1-2).
Sometimes it occurs because people do not or cannot eat enough of the foods that provide the essential nutrients to satisfy body needs. At other times people may eat well-balanced diets but suffer from dis-eases that prevent normal usage of the nutrients.
Overnutrition has become a larger problem in the United States than undernutrition. Overeating and the ingestion of megadoses of various vitamins and minerals (without prescription) are two major causes of overnutrition in the United States.
A nutrient deficiency occurs when a person lacks one or more nutrients over a period of time. Nutrient deficiencies are classified as primary or secondary. Primary deficiencies are caused by inadequate dietary intake. Secondary defi-ciencies are caused by something other than diet, such as a disease condition that may cause malabsorption, accelerated excretion, or destruction of the nutrients. Nutrient deficiencies can result in malnutrition.