Energetic adaptation to chronic disease in the elderly.

Several chronic diseases occur with increased prevalence in the elderly. Body weight loss is a common feature of many chronic diseases. Weight loss increases the risk for morbidity and mortality and contributes to decreased functional independence and poor quality of life. Thus, an understanding of the effect of chronic disease on energy balance has important implications for nutritional supplementation and clinical outcome. This brief review will consider recent studies that have examined the effect of several chronic diseases (i.e., Alzheimer's disease, Parkinson's disease, and congestive heart failure) on daily energy expenditure in elderly individuals. Additionally, we put forth a model to explain the energetic adaptation to chronic disease in the elderly that is based on measurements of daily energy expenditure and its components. Studies suggest that chronic disease decreases daily energy expenditure in elderly individuals due to a marked reduction in physical activity energy expenditure. Moreover, these changes in daily energy expenditure often occur in the presence of increased resting energy expenditure. Thus, the net effect of chronic disease is to decrease daily energy expenditure. These results do not favor the hypothesis that increased energy expenditure contributes to disease-related weight loss. Instead, reduced energy intake appears to be a more likely mediator of the negative energy imbalance and weight loss that frequently accompany chronic disease in the elderly.