Moderators of a Diet and Physical Activity Intervention: who Responds Best to Sequential vs. Simultaneous Approaches.

Background: Given that low physical activity levels and poor dietary intake are co-occurring risk factors for chronic disease, there is a need for interventions that target both health behaviors, either sequentially or simultaneously. Little is known about participant characteristics that are associated with better or worse response to sequential and simultaneous interventions.

Method: The 12-month Counseling Advice for Lifestyle Management (CALM) randomized trial (N = 150; M_age = 55.3 years) targeted these two behaviors either via a sequential approach - dietary advice first then exercise advice added ("Diet-First") or exercise advice first then dietary advice added ("Exercise-First") - or via a simultaneous approach. The objective was to examine demographic, clinical, and psychosocial moderators of intervention effects on 12-month change in (1) moderate-to-vigorous physical activity (MVPA), (2) fruit/vegetable intake, (3) caloric intake from saturated fat, and (4) weight. Hierarchical regressions first compared Diet-First to Exercise-First, followed by comparisons of these arms combined ("sequential") to the simultaneous arm.

Results: Older age, higher baseline BMI, and lower social support were associated with higher MVPA in Exercise-First vs. Diet-First, while lower tangible support was associated with higher fruit/vegetable intake in Exercise-First but not in Diet-First. Poor sleep was associated with higher levels of MVPA in the sequential arm than in the simultaneous arm. Lower vitality was associated with greater weight loss in the sequential arm than in the simultaneous arm, while the opposite was true for those who were not married.

Conclusion: Identifying moderators of treatment response can allow the behavioral medicine field to enhance intervention efficacy by matching participant subgroups to their best-fitting interventions.

Trial registration: NCT00131105.