Drs. Singh and Musialek suggest that patients with heart failure should be stratified on the basis of disease severity and cardiac output and then that it should be determined whether the resting metabolic rate varies among patients with New York Heart Association class II to IV heart disease. In our initial study, however, this question could not be rigorously addressed because of the limited number (n = 4) of patients with functional class IV disease. Additional studies with larger sample sizes are needed to adequately address whether the degree of cardiac compensation is related to abnormalities in energy metabolism.

Drs. Singh and Musialek point out that energy requirements may also differ between patients with heart failure and healthy elderly persons because of differences in the thermic effect of a meal. It is presently unknown whether the energy expenditure associated with meal ingestion differs between healthy persons and patients with heart failure. However, this component constitutes a small amount of total daily energy expenditure (approximately 10%) [1] and thus is not likely to be a major factor implicated in cardiac cachexia. Conceptually, we believe that using the doubly labeled water method to examine total daily energy expenditure and free-living physical activity in patients with heart failure is a logical next step. The assessment of daily energy expenditure can serve as a proxy measure of daily energy needs in patients with heart failure. The use of this technology can accurately predict the total daily energy needs and assist in the nutritional management of these frail patients. We hope our work generates new studies that further the understanding of unexplained weight loss and nutritional problems in patients with heart failure.