Body composition of patients with Alzheimer's disease.

Low body weight is frequently reported in patients with Alzheimer's disease. We sought to discover why by comparing the body composition of 28 cognitively normal elders and 23 institutionalized individuals with Alzheimer's disease. Body mass index was calculated from standing height and weight. Percentages of lean body mass, body fat, and body water were derived from bioimpedance measurements of resistance and reactance. Skinfold thickness was measured at seven body sites to estimate regional fat distribution. Variables were analyzed by analysis of variance with subjects grouped by cognitive status within gender. Activity level and age were not significant covariates. Both women and men with Alzheimer's disease weighed less than control subjects. Differences in body composition were more pronounced in women with Alzheimer's disease, who had lower body mass index (22.0 +/- 3.0 vs 26.1 +/- 5.1), higher percentage of lean body mass (73.8 +/- 5.1 vs 66.9 +/- 6.5), lower percentage of body fat (26.1 +/- 5.1 vs 33.1 +/- 6.5), and higher percentage of body water (55.8 +/- 5.0 vs 49.3 +/- 6.5) compared with control women. Except for lower body weight, the body composition of men with Alzheimer's disease was not significantly different from that of control men. Patients of both sexes with Alzheimer's disease had less truncal body fat compared with controls, which gave them a youthful body habitus. These differences were not accounted for by age, diet, or activity. Our findings indicate that patients with Alzheimer's disease have lower body weight and may require higher energy intake than cognitively normal elders.