Diet and exercise intervention adherence and health-related outcomes among older long-term breast, prostate, and colorectal cancer survivors

Abstract

Given the numerous benefits of a healthy diet and exercise for cancer survivors, there has been an increase in the number of lifestyle intervention trials for this population in recent years. However, the extent to which adherence to a diet and exercise intervention predicts health-related outcomes among cancer survivors is currently unknown. To address this question, data from the Reach out to ENhancE Wellness in Older Cancer Survivors (RENEW) diet and exercise intervention trial were analyzed. RENEW was a yearlong telephone and mailed print intervention for 641 older (>65 years of age), overweight (body mass index: 25.0-39.9), long-term (>5 years post-diagnosis) survivors of colorectal, breast, and prostate cancer. Participants were randomized to the diet and exercise intervention or a delayed-intervention control condition. The RENEW telephone counseling sessions were based on determinants of behavior derived from Social Cognitive Theory (SCT) (e.g., building social support, enhancing self-efficacy). These factors have been hypothesized to improve health behaviors, which in turn should improve health outcomes. Thus, drawing on SCT and prior diet and exercise research with cancer survivors, I hypothesized that telephone counseling session attendance would be indirectly related to health-related outcomes (i.e., physical function, basic and advanced lower extremity function, mental health, and body mass index) through intervention-period strength and endurance exercise and dietary behavior (i.e., fruit and vegetable intake, saturated fat intake). The proposed model showed good fit to the data; however, not all of the hypothesized relationships were supported. Specifically, increased telephone counseling session attendance was related to engagement in all of the health behaviors over the intervention period. In turn, (a) increased endurance exercise was related to improvement in all of the health-related outcomes with the exception of mental health; (b) increased strength exercise was solely related to improved mental health; (c) increased fruit and vegetable intake was only related to improved basic lower extremity function; and (d) saturated fat intake was not related to any of the health-related outcomes. Taken together, these findings suggest that SCT determinants of behavior and the importance of session attendance should continue to be emphasized in diet and exercise interventions. Continued exploration of the relationship between adherence to a diet and exercise intervention and health-related outcomes will inform the development of more cost-effective and efficacious interventions for cancer and other medical populations.