Behaviour change theories can help provide systematic explanations for why certain interventions promote changes in lifestyle habits. The Theory of Planned Behaviour (TPB) is one of the most widely accepted behavioural theories and suggests that a person's likelihood of carrying out a planned behaviour is influenced by: attitudes, about the likely consequences of a given behaviour; subjective norms, relating to beliefs about the expectations of others; and perceived behavioural control, relating to the perception of factors that may assist or impede certain behaviours.
Previous studies have demonstrated that providing genetic information and advice can help to motivate changes in nutrition and physical activity (PA) among patients, but the theoretical mechanism behind this phenomenon is poorly understood.
The purpose of the present study, conducted by researchers from The University of Western Ontario, Canada, was to determine and compare the impact of providing genetically tailored or population-based lifestyle advice for weight management on key constructs of the TPB.
A pragmatic, cluster randomised controlled trial (n = 140) was carried out by the East Elgin Family Health Team, in Canada. Participants were primarily females enrolled in a weight management program (BMI ≥ 25.0 kg/m2). Groups were randomised (1:1) to receive a population-based (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.
Overall, the researchers found significant changes (improvements) in attitudes towards the effectiveness of the nutrition and PA recommendations for weight management were similar in the GLB and GLB+LGx groups, though changes tended to be more long-term in the GLB+LGx group.
Changes in subjective norms also tended to be more long-term in the GLB+LGx group, with significant changes in five subjective norm measures observed in this group. Notably, there were significant long-term changes in subjective norms related to both friends and family consuming a healthy diet.
The results also indicated increases in the perceived difficulty of changing protein intake in the standard GLB group, but not the GLB+LGx group.
The report states: "Overall, our results indicate that the provision of genetically tailored lifestyle information and advice tended to impact antecedents of behaviour change, more so over the long term through within-group analyses while population-based advice tended to impact antecedents of behaviour change more over the short term through within-group analyses (e.g., attitudes towards dietary fat intake, perceptions that friends and family consume a healthy diet and perceptions about the impact of genetic-based advice for weight management).
"These findings directly relate to previously published NOW trial results."
"...population-based research consistently indicates that nutrition interventions impact short-term dietary changes, but long-term dietary changes remain challenging... Nutrigenetic interventions could help to mitigate this problem."
There have been only four long-term (12-month) RCTs assessing changes in nutrition in genetic interventions compared to population-based interventions [8,9,11,20,24]. All of these RCTs have demonstrated that long-term nutrition-related behaviour change was greater with the addition of genetic-based information/advice. Thus, the current research suggests a potential explanation of these long-term findings, guided by the TPB.
Madill. J., et al
"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"