Unintentional weight loss is always associated with a poor prognosis. A body mass index (BMI "body mass index" - body weight in kilograms divided by the square of the individual's body height in meters) of less than 22 is regularly associated with higher one-year mortality, impaired functional status of the elderly compared to the community of individuals of the same age. The higher risk of mortality begins at a BMI of less than 22 for both sexes at the age of 65 and older. For men older than 75 years with a BMI index value of less than 20.5, the risk of mortality is increased by 20%. Similarly, women over 75 with a BMI of less than 18.5 have a 40% increased risk of mortality. This phenomenon refers specifically to recent weight loss. For example, a decrease in body weight of 10% or more in seniors older than 50 years is associated with an increase in mortality by 60% compared to individuals with a stable body weight. For patients hospitalized in a hospital or nursing facility, a 10% decrease in body weight in the last 6 months significantly predicts increased mortality in the following 6 months. Patients who have lost 5% of body weight are characterized by a 5-10-fold increase in the risk of death.
However, the decrease in body weight is also associated with a significant decrease in the functional status of the elderly. A loss of more than 5% in women's body weight between the ages of 60 and 74 is associated with a two-fold increase in the risk of self-sufficiency compared to women at a stable body weight. An important finding when monitoring body composition is the fact that an unintentional decrease in body weight is at the expense of a loss of lean - active body mass. In fact, the largest part of this deficit is the loss of muscle mass and only a smaller part of the reduction of fat tissue.