Exploring Attitudes, Subjective Norms and Perceived Behavioural Control in a Genetic-Based and a Population-Based Weight Management Intervention: A One-Year Randomized Controlled Trial

Abstract

Background: Several studies demonstrate that the provision of personalized lifestyle advice, based on genetics, can help motivate individuals to engage in greater nutrition and physical activity changes compared to the provision of population-based advice. The theoretical mechanism behind this phenomenon is poorly understood. The objective of this study was to determine the impact of providing genetically tailored and population-based lifestyle advice on key constructs of the Theory of Planned Behaviour (TPB).

Materials and methods: A pragmatic, cluster randomized controlled trial (n = 140) took place at the East Elgin Family Health Team, in Aylmer, Ontario, Canada. Participants were primarily Caucasian females enrolled in a weight management program (BMI ≥ 25.0 kg/m2). Weight management program groups were randomized (1:1) to receive a population-based lifestyle intervention for weight management (Group Lifestyle Balance™ (GLB)) or a lifestyle genomics (LGx)-based lifestyle intervention for weight management (GLB+LGx). Attitudes, subjective norms and perceived behavioural control were measured at baseline, immediately after receiving a report of population-based or genetic-based recommendations and after 3-, 6- and 12-month follow-ups. Linear mixed models were conducted, controlling for measures of actual behavioural control. All analyses were intention-to-treat by originally assigned groups.

Results: Significant changes (p < 0.05) in attitudes, subjective norms, and perceived behavioural control tended to be short-term in the GLB group and long-term for the GLB+LGx group. Short-term and long-term between-group differences in measures of subjective norms were discovered, favouring the GLB+LGx group.

Conclusions: The TPB can help provide a theoretical explanation for studies demonstrating enhanced behaviour change with genetic-based lifestyle interventions.

Clinical trial registration: NCT03015012.

Keywords: behaviour change; behavioural determinants; lifestyle genomics; nutrigenetics; nutrigenomics; personalized nutrition; randomized controlled trial; theory of planned behavior; theory of planned behaviour.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

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Flow of study design. TPB: Theory of Planned Behaviour; GLB: Group Lifestyle Balance™; LGx: lifestyle genomics.

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Figure 3

Stages of change by time point and group. Stage of change was measured on a Likert scale of 1 through 6 based on the transtheoretical model (stages of change); 1 represented pre-contemplation, 2 represented contemplation, 3 represented motivation, 4 represented action (6 months). Asterisks indicate significant differences from run-in (pre-intervention), within groups: p ≤ 0.001 at all time points in both groups. GLB (n = 70 with mean value imputation): Run-In 3.50 ± 0.18 (mean ± SE), 95% CI: 3.10–3.82; Baseline 3.76 ± 0.18, 95% CI: 3.41–4.12; 3 Months* 4.15 ± 0.15, 95% CI: 3.85–4.44; 6 Months* 4.37 ± 0.17, 95% CI: 4.03–4.70; 12 Months* 4.26 ± 0.19, 95% CI: 3.89–4.63. GLB+LGx (n = 70 with mean value imputation): Run-In 3.77 ± 0.16 (mean ± SE), 95% CI: 3.46–4.09; Baseline 3.70 ± 0.15, 95% CI: 3.40–4.00; 3 Months* 4.27 ± 0.12, 95% CI: 4.02–4.51; 6 Months* 4.62 ± 0.14, 95% CI: 4.33–4.90; 12 Months* 4.70 ± 0.16, 95% CI: 4.39–5.02. GLB: Group Lifestyle Balance™; LGx: lifestyle genomics.