In later life a high body mass index (BMI) is associated with the lowest age-related mortality rate. The BMI range used by the World Health Organization (WHO) to classify overweight, a BMI of 25-30 kg/m2, can be regarded as normal weight in old age; nevertheless, obesity is associated with an increased risk of disability and of a deterioration in physical functionality, particularly among older age groups. This relationship to obesity has also been established for frailty. For this reason, a reduction in weight may be appropriate under functional aspects if BMI values exceed 30 kg/m2; however, such a decision cannot be made on the basis of an individual BMI alone. The functional status, body composition, comorbidities and, in particular the life perspectives of the patient should also be taken into consideration. If weight loss is intended, it must always be performed under strict medical supervision involving optimized protein intake, a carefully calculated moderate reduction in calories and adequate physical training. In the case of chronically ill elderly patients, weight reduction is not usually appropriate. Restrictive diets of any kind should principally be critically viewed in old age because even temporary inadequate energy intake may lead to accelerated deterioration of muscle and bone structure.
Keywords: Aging; Body mass index; Mortality; Overweight; Physical function.