Delving into the Paradox of COPD and Obesity
Sabino, G. P., Silva, B. M., Brunetto, A. F. (2010). Nutritional status is related to fat-free mass, exercise capacity and inspiratory strength in severe chronic obstructive pulmonary disease patients. Clinics, 65(6), 599-605.
Previous studies report conflicting results in terms of the influence of being overweight or obese on exercise capacity in patients with severe Chronic Obstructive Pulmonary Disease (COPD). A recent study in Brazil set out to investigate the impact of nutritional status on body composition, exercise capacity, and respiratory muscle strength in these patients. Considering that the major contributor to fat free mass (FFM) is skeletal muscle mass, these researchers considered that the greater FFM in overweight/obese patients would lead to greater exercise capacity (in part due to greater respiratory muscle strength), which in part would lead to greater survival rate. This paradox seems odd, that there is a lower risk of death in being overweight or obese in anyone; however, given that FFM (as well as exercise capacity) is associated with functional capacity, the presence of more FFM in these patients with COPD may be, at least partly, the reason.
Thirty-two patients, including nine women, participated in the study.
Participants were divided into three groups according to BMI:
- Overweight/obese = 8 individuals (25 ≤ BMI ≤ 34.9 kg/m2)
- Normal weight = 17 individuals (18.5 ≤ BMI ≤ 24.9 kg/m2)
- Underweight = 7 individuals (BMI <18.5 kg/m2)
Airway obstruction was similar among the groups; however, severe COPD patients who were overweight or obese had greater fat free mass, exercise capacity, and inspiratory muscle strength than patients with the same level of COPD who were of normal or low weight.
These results suggest that the overweight/obese patients in this study had higher exercise capacity due to their higher FFM. Since we know that exercise capacity is strongly related to prognosis for many conditions and studies have shown that overweight/obese patients present higher exercise capacity (than under- or normal weight), this relationship may present a reasonable mechanism for why these overweight/obese patients may receive a better prognosis. Not only did this study find that these patients had a greater FFM, but also higher respiratory muscle strength, which is associated with better functional status as well as greater FFM. Both of these factors could also help explain this paradox of prognoses.
This study was unable to differentiate COPD subtypes (chronic bronchitis versus emphysema-type COPD, the latter of which typically exhibits an increased loss in FFM). This study also analyzed the obese patients together with the overweight patients due to the number participating, though ideally, these groups would be separated, given the potential that those with more severe obesity may present with lower exercise capacity and other possible dysfunctions associated with metabolic syndrome.
Given these findings and limitations, other studies using mortality as an endpoint are needed to confirm that FFM, exercise capacity, and respiratory muscle strength actually do promote longer life in overweight/obese severe COPD patients.
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