Malnutrition is a common cause and consequence of illness, particularly in older people. The number of malnourished people leaving NHS hospitals in England has risen by 85% over the past 10 years. It is still rising and reached almost 140 000 in 2006-7.1 Surveys elsewhere consistently find that about 20% of patients in general hospitals are malnourished (body mass index <18.5 (the World Health Organization 1995 cut off for malnutrition), or thin and losing weight, or both). Figures are higher if specific nutrient deficiencies or functional indications of malnutrition are included.

Despite the frequency of malnutrition, it is undiagnosed in up to 70% of patients. This is partly because of the lack of simple laboratory tests, and because biochemical tests for nutritional status are difficult to interpret, particularly as they are often influenced by acute phase responses to …