Nutritional status and interventions
Chronic obstructive pulmonary disease
As with other chronic diseases, COPD is often accompanied by abnormalities of body composition. This can mean loss of muscle bulk and cachexia (‘wasting’), but also, increasingly, it means obesity. Various indices can signify under-nutrition in COPD: these include a BMI of <21 kg·m-2, involuntary loss of more than 5% of total bodyweight in the past year, and a low fat-free mass index (<15 kg·m-2 in women or <16 kg·m-2 in men).
Nutritional depletion in COPD results from multiple and complex mechanisms, and nutritional intervention alone cannot address all of the issues raised. Consequently, clinical guidelines recommend nutritional intervention in the context of pulmonary rehabilitation in all patients with COPD, particularly in those who are already nutritionally depleted. After decades of scepticism, nutritional intervention aimed at restoring fat-free mass is now recommended and a recent meta-analysis of original data has shown a positive benefit from such supplementation. Nutritional intervention in COPD should be integrated into pulmonary rehabilitation, both at an early stage and in end-stage disease when patients are on long-term oxygen therapy and/or noninvasive ventilation.
Allergies and asthma
Epidemiological findings underscore the importance of conducting prospective studies and clinical trials to clarify the role of antioxidants, omega-3 polyunsaturated fatty acids and vitamin D in asthma and wheezing, in both children and adults. Further studies are also needed to better understand how dietary habits might modulate asthma severity and/or control in adults. A recent exhaustive review of the association between asthma and diet concluded that until the results of forthcoming trials are available, the practical consequences of research linking diet with asthma are minimal, and, based on current evidence, people with asthma, pregnant women, parents, and children should not be advised to change or supplement their diet to treat or reduce the risk of developing asthma.
Clinical epidemiological studies suggest a strong relationship between obesity and poor control of asthma, and treatment by bariatric surgery has been advocated to control very severe cases.
Nutritional principles indicate that a healthy diet should include at least moderate amounts of fruit and vegetables, but the available data suggest that general increases in fruit and vegetable intake would have little effect on cancer rates, at least in well-nourished populations. Advice in relation to diet and cancer should include the recommendation to consume adequate amounts of fruit and vegetables, but should put most emphasis on the well-established adverse effects of obesity and high alcohol intake. Specific nutritional intervention in patients treated for lung cancer has not resulted in a better quality of life.
Obstructive sleep apnoea syndrome and obesity hypoventilation syndrome
Obesity, especially affecting the trunk and neck, is a major risk factor for obstructive sleep apnoea syndrome (OSAS); although other factors may contribute to its pathogenesis, obesity is reported in 60–90% of individuals with OSAS. Patients with obesity hypoventilation syndrome (OHS) usually have very severe obesity, often in the ‘morbid’ range (a BMI of >40 kg·m-2). Although OHS is much less common than OSAS, its prevalence is increasing in many countries, in parallel with the ‘epidemic’ of obesity in the population. Either OSAS or OHS may coexist with COPD, particularly in smokers, increasing morbidity. Weight loss may lead to resolution of OSAS or OHS but, even if successful, this is likely to take several months and in severely obese individuals, bariatric surgery may be indicated. Effective treatment of the breathing problems should not be delayed while waiting for weight loss to occur (see chapter 23).
A major area of recent progress in cystic fibrosis has been the emphasis on the central role of under-nutrition. The patient’s diet and BMI are monitored very closely, and pancreatic enzyme supplementation should be used to combat pancreatic insufficiency.
Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis is a cause of severe weakness of the respiratory muscles. Enteral nutrition (feeding directly into the stomach or lower down the digestive tract), together with noninvasive ventilation can offer palliation and prolongation of life with acceptable side-effects. Percutaneous endoscopic gastrostomy (PEG) should be considered to stabilise weight and to prolong survival.