Background: Patients who participate in cardiac rehabilitation (CR) following myocardial infarction experience more effective overall secondary prevention compared to those who do not participate. However we know little of the effects of CR on major risk factors such as body composition. Moreover, while cardiac patients are encouraged to stop smoking, the effect of this change on body composition during CR is unknown. This study aimed to examine the changes in body composition following completion of a Sydney hospital-based CR program and 6-month follow-up.
Methods: Participants entering a hospital-based CR program underwent a treadmill exercise stress test (Bruce protocol) and body composition assessment (waist circumference; weight, body fat, visceral fat (VAT) assessed via bioelectrical impedance analysis). Measurements were repeated at CR-completion and 6-month follow-up. Smoking status was assessed at each time point, and confirmed by measurement of exhaled carbon monoxide. One-way ANOVA was used to examine differences across time for those reporting smoking at baseline who successfully quit smoking by 6-months, and non-smokers.
Results: Of 159 patients with complete data, n=27 reported smoking at baseline, all but four of whom quit smoking by 6-months. Smokers were younger than non-smokers (56.1±11.4 vs. 62.4±11.8years, p<0.001), with less body fat (27.9±6.6% vs. 31.3±8.7%, p=0.006) and more skeletal muscle (33.6±2.9% vs. 31.1±4.7%, p<0.001). Group x time interactions were seen for weight (p=0.002), body fat (p=0.037), VAT (p=0.004), muscle mass (p=0.012) and waist circumference (p=0.010), with non-smokers showing favourable changes at CR-completion and 6-months compared to ex-smokers. Fitness improvements were similar between groups.
Conclusions: Quitting smoking is of utmost importance for reducing cardiovascular risk. However, while CR improves body composition outcomes in non-smokers, those who quit smoking may experience adverse changes to body composition even in the face of successful CR completion. These patients may need increased support to minimise negative changes to body composition.