As we grow older changes in body composition occur. These changes include a loss of lean body mass (LBM), bone mass, body water, and a relative increase of fat mass. In view of these changes and acknowledging demographic trends, elder people are facing a growing burden of health-compromising levels of their weight, including underweight, overweight, and its combination. At all ages weight control is relevant, but in older people, it preferably occurs under professional guidance in view of the effect of body composition on mortality, morbidity, and functioning. Hereby, due attention needs to be given to the role of disease, physical activity, and other determinants of either weight gain or weight loss. For both a critical use of currently recommended cutoff points for BMI and WC is warranted in aging populations.