DAILY ENERGY-EXPENDITURE IN FREE-LIVING NONINSTITUTIONALIZED ALZHEIMERS PATIENTS - A DOUBLY LABELED WATER STUDY

Weight loss is common in Alzheimer's disease (AD), but its pathogenesi s is poorly understood. It is unclear whether an elevated daily energy expenditure contributes to the weight loss. We tested the hypothesis that daily energy expenditure is higher in AD patients compared to hea lthy elderly. Thirty AD (73 +/- 8 years; Mini-Mental State Examination score: 16 +/- 8) and 103 healthy elderly (69 +/- 7 years) were charac terized for daily energy expenditure and its components (resting and f ree-living physical activity energy expenditure) from doubly labeled w ater and indirect calorimetry. Fat-free mass and fat mass were measure d from dual energy X-ray absorptiometry. Fat-free mass tended to be lo wer in AD patients (45 +/- 9 kg) versus healthy elderly (49 +/- 10 kg; p = 0.07), whereas no differences were noted in fat mass between grou ps. Daily energy expenditure was 14% lower in AD (1901 +/- 517 kcal/d) compared to healthy elderly (2213 +/- 513 kcal/d; p < 0.001), due to lower resting (1287 +/- 227 versus 1418 +/- 246 kcal/d; p < 0.01) and physical activity energy expenditures (425 +/- 317 versus 574 +/- 342 kcal/d; p < 0.05). No differences in energy expenditure were noted bet ween groups after controlling for differences in body composition. Dai ly energy expenditure was examined in a subgroup (n = 11) of AD patien ts who lost significant body weight (5.6 +/- 2.3 kg) within the past y ear. There was a lower daily energy expenditure in cachectic AD patien ts (1799 +/- 474 kcal/d) versus non-cachectic patients (1960 +/- 544 k cal/d) and healthy elderly (2213 +/- 513 kcal/d; p < 0.01). Similarly, no differences in energy expenditure were noted between groups after controlling for differences in body composition. We conclude that abso lute levels of daily energy expenditure are lower in AD patients due t o their lower body mass. However, after taking into account difference s in body composition, daily energy expenditure in AD patients is appr opriate for their metabolic size, The hypothesis that elevated daily e nergy expenditure contributes to weight loss in AD is not supported by these findings.