The prevalence of malnutrition varies between 30% and 60% in different patient groups with chronic obstructive pulmonary disease (COPD); it is highest in patients with emphysema [90, 91]. Since
Vandenbergh first reported a shorter 5-year survival rate in COPD patients with weight loss 30 years ago , it has been well documented that low body weight is an independent predictor of morbidity and mortality in COPD patients [93-96]. Even after adjusting for age, gender, smoking status, and especially FEV1 and home oxygen use, Gray-Donald and colleagues showed that a low BMI has an independent effect on all-cause mortality . A large cohort of over 4,000 severe COPD patients treated with long-term oxygen therapy confirmed an ongoing premise that survival rates improve with increasing BMI and are best in the obese population . In this study, patients with low BMIs (< 20kg/m2) had the worst 5-year survival rate (24%). The BMI was the most powerful predictor of rate of hospitalization and length of stay .
Malnutrition in patients with COPD is associated with an imbalance between energy expenditure and dietary intake . COPD patients have higher energy needs, despite their seemingly low level of physical activity, which can be explained by the inefficiency of the peripheral skeletal muscles and thus overcompensation of the respiratory muscles. The increased work of breathing and the greater respiratory muscle activity account for the increased resting energy expenditure (REE). The functional consequences of nutritional depletion not only relate to muscle wasting (e.g., loss of lean body mass), but also to alterations in muscle morphology and metabolism. Malnutrition is known to affect types of diaphragm muscle fibers, potentially influencing contractility and fatigue . Clinically, malnourished COPD patients are predisposed to pulmonary infections and failure to wean from mechanical ventilation from adverse effects on muscle strength , ventilatory drive , and immune defense mechanisms . Hyperinflation-induced early satiety and poor appetite are the major factors contributing to insufficient energy intake in COPD patients. Medication use, chronic systemic inflammatory response, and negative nitrogen balance also contribute to the nutritional depletion of COPD patients .
The association of malnutrition and weight loss with advanced lung disease has been termed pulmonary cachexia syndrome. General nutritional goals for these patients include preservation of lean body mass by providing adequate energy and protein to produce a positive nitrogen balance. The importance of medical nutrition therapy for COPD patients is widely accepted and successful in improving weight and muscle strength, but nutritional support trials have shown little in improved outcomes and provided mixed results. Most of the randomized controlled trials with oral supplementation, particularly in short-term studies, note positive effects on respiratory function and respiratory muscle strength, but offer no comment on mortality . However, poor treatment responses might be attributed to limitations such as non-compliance, individual variation, and the observation that patients take the supplements instead of their regular meals. In a Cochrane review of randomized controlled trials of nutritional interventions lasting at least 2 weeks, Ferreira and colleagues concluded that prolonged nutritional supplementation had no benefit on lung function, anthropometric measurements, or exercise capacity in stable COPD patients . This result was homogeneous across all studies. Other studies evaluating the effects of adjuvant treatments with anabolic steroids and growth hormone in COPD patients showed improvements in body weight and lean body mass, but not in functional capacities [106-108]. Hypercarbic COPD patients fed a high-fat, low-carbohydrate diet have shown weight gain  and improvements in respiratory function [110, 111] and exercise capacity . Overall, most nutritional supplementation studies show improvements in predictors of survival in COPD patients, but evidence confirming survival benefits is lacking.
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