Normal ageing is associated with changes in eating behaviour and body composition. The body weight (or BMI) associated with greatest life expectancy increases with age, and is 27-28 kg/m2 in people > 70 years, compared to < 25 kg/m2 in younger adults, yet on average older people lose body weight after about age 65 years. This weight loss is often involuntary, and related to the physiological decline in appetite that accompanies normal ageing (“anorexia of ageing”). The causes of this appetite decline are multiple, but include reduced sense of smell and taste, slowing of gastric emptying and possibly hormonal changes such as increased activity of the satiating hormone cholecystokinin. When pathological factors, such as depression, inflammation, malignancy and social isolation, are superimposed, weight loss can become excessive and lead to pathological under-nutrition. The association between weight loss (particularly if > 5% and involuntary) and/or low body weight (BMI < 22 kg/m2) and adverse outcomes, has been demonstrated clearly in older people. This is related, at least in part, to the body composition changes accompanying ageing. As people age they lose skeletal muscle, and when they lose weight the tissue lost is disproportionately skeletal muscle. In contrast, ageing is associated with in overall increase in fat stores and a redistribution of these stores to be intrahepatic, intramuscular and intra-abdominal (cf subcutaneous) deposits. When excessive the loss of skeletal muscle leads to sarcopaenia and frailty, which are particularly associated with adverse outcomes, including reduced quality of life and increased morbidity, need to move into higher level accommodation, and mortality. Approaches to under-nutrition and sarcopaenia shown to be of benefit in older people include identification and correction of underlying causes, the use of protein-enriched nutritional supplements and exercise programs (particularly resistance exercise), but not, to date, the use of anabolic hormones.