Hypermetabolism can explain why some COPD patients lose weight despite an apparent normal to even high dietary intake. Nevertheless, it has been shown that dietary intake in weight-losing patients is lower than in weight-stable patients both in absolute terms and in relation to measured REE . This is quite remarkable because the normal adaptation to an increase in energy requirements in healthy men is an increase in dietary intake. The reasons for a relatively low dietary intake in COPD patients are not completely understood. It has been suggested that they eat suboptimally because chewing and swallowing change the breathing pattern and decrease arterial oxygen saturation. Furthermore, gastric filling in these patients may reduce the functional residual capacity and lead to an increase in dyspnoea. Very intriguing is the role of leptin in energy homeostasis. This adipocyte-
derived hormone represents the afferent hormonal signal to the brain in a feedback mechanism regulating fat mass. In addition, leptin has a regulating role in lipid metabolism and glucose homeostasis, increases thermogenesis, and has effects on T-cell-mediated immunity. There are few data on leptin metabolism in COPD. Circulating leptin levels correlate well with BMI and fat percentage in COPD patients, as expected, but the values were significantly lower than in healthy subjects . In experimental studies, the administration of endo-toxins or cytokines produced a prompt increase in serum leptin levels . One study also observed a relationship between leptin and soluble TNF-receptor 55 in COPD patients, in particular those with the emphysematous sub-type. Leptin levels as well as those of soluble TNF-receptor 55 were, in turn, inversely related to dietary intake in absolute terms as well as adjusted for REE . The exact regulation of leptin in COPD needs further exploration. Another factor of interest in evaluating dietary intake is the influence of psychological dysfunctioning, such as anxiety, depression, and appetite. Although no systematic studies have been reported thus far, limited physical abilities, financial constraints and lack of supportive care of COPD patients should also be considered as factors that may interfere with dietary intake.
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