Results Of the 100 enrolled participants, 26 participants were randomized to exercise; 24 to diet; 25 to exercise + diet; 25 to control. Of these, 92 participants completed the trial. Exercise attendance was 84% (SD, 14%) and diet adherence was 99% (SD, 1%). By main effects analysis, peak V̇ o 2 was increased significantly by both interventions: exercise, mL/kg body mass/min (95% CI, to ), P < .001; diet, mL/kg body mass/min (95% CI, to ), P < .001. The combination of exercise + diet was additive (complementary) for peak V̇ o 2 (joint effect, mL/kg/min). There was no statistically significant change in MLHF total score with exercise and with diet (main effect: exercise, −1 unit [95% CI, −8 to 5], P = .70; diet, −6 units [95% CI, −12 to 1], P = .08). The change in peak V̇ o 2 was positively correlated with the change in percent lean body mass ( r = ; P = .003) and the change in thigh muscle:intermuscular fat ratio ( r = ; P = .02). There were no study-related serious adverse events. Body weight decreased by 7% (7 kg [SD, 1]) in the diet group, 3% (4 kg [SD, 1]) in the exercise group, 10% (11 kg [SD, 1] in the exercise + diet group, and 1% (1 kg [SD, 1]) in the control group.
Genetics play a role in the development of COPD.  It is more common among relatives of those with COPD who smoke than unrelated smokers.  Currently, the only clearly inherited risk factor is alpha 1-antitrypsin deficiency (AAT).  This risk is particularly high if someone deficient in alpha 1-antitrypsin also smokes.  It is responsible for about 1–5% of cases   and the condition is present in about 3–4 in 10,000 people.  Other genetic factors are being investigated,  of which there are likely to be many. 
Symptom severity is assessed using the CAT or mMRC ( table 7 ) [ 103 ]. Lung function in addition to the number of exacerbations and hospitalizations for exacerbations in the previous 12 months can be used to predict future risk. A history of zero or one exacerbation in the past 12 months and GOLD 1 or 2 spirometric level suggests a low future risk of exacerbations, while two or more exacerbations or a hospitalized exacerbation or GOLD 3 or 4 spirometric level suggest a high future risk [ 8 ]. These components are combined into four groups as follows: