Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy


Health and Rehabilitation Sciences


Gilliland, Jason A

2nd Supervisor

Madill, Janet



Background: The impact of nutrigenomics and lifestyle genomics interventions on health outcomes and behaviours remains controversial and under-explored.

Objectives: To determine the short-term (3-month), moderate-term (6-month) and long-term (12-month) impact of providing personalized, genetic-based lifestyle information and advice on anthropometric measures, as well as dietary intake and adherence.

Methods: The nutrigenomics, overweight/obesity and weight management trial (NOW Trial) is a pragmatic randomized controlled trial that was incorporated into the Group Lifestyle Balance™ (GLB) program (N=140). Inclusion criteria: overweight or obesity (BMI ≥ 25 kg/m2), ≥ 18 years of age, English-speaking, having access to internet at least one day per week, willing to undergo genetic testing, and not seeing another healthcare provider outside of the study for weight-loss advice. Exclusion criteria: Pregnancy and lactation. Twelve-month GLB weight management program groups were randomized 1:1 to receive either the standard GLB program or a modified nutrigenomics-based GLB program (GLB+NGx). Data collection occurred at baseline, 3-, 6- and 12-month follow-up. The predetermined primary outcome was change in body fat percentage (BFP). Dietary intake and adherence were secondary outcome measures.

Statistical Analysis: Statistical tests conducted using SPSS (version 26.0) included: repeated measures analyses of variance (ANOVAs), split-plot ANOVAs, two-way ANOVAs, chi-square and Fisher’s exact tests and logistic regression. Key components of the Theory of Planned Behaviour were considered in the dietary intake analyses.

Results: After 3- and 6-month follow-up, the GLB+NGx group improved (reduced) their BFP to a significantly greater extent (p<0.05) than the standard GLB group. There were no statistically significant differences in BFP between groups after 12 months. Furthermore, the GLB+NGx group significantly reduced their total fat intake after 12 months; the standard GLB group did not. Dietary adherence to saturated fat and total fat recommendations were significantly (p<0.05) greater in the GLB+NGx group compared to the standard GLB group at 12 months.

Conclusion: Genetically-tailored lifestyle advice can lead to improvements in body composition over the short-term and moderate-term, and motivate long-term dietary changes and adherence to nutrition recommendations. Biological mechanisms may challenge long-term weight loss, even with genetically-tailored advice that motivates long-term dietary changes.

Summary for Lay Audience

Nutrigenomics is a science that explores how our genes impact the way our bodies respond to the foods, beverages and nutrients we consume. For example, one person may lose more weight by following a lower saturated fat nutrition plan compared to someone else. Nutrigenomics can be used to provide more personalized nutrition advice. Some studies have shown that giving personalized, genetic-based information and advice can help motivate individuals to make dietary changes. Very few studies have assessed the effectiveness of nutrigenomics-based weight loss interventions. Therefore, the studies included in this dissertation aimed to build upon past research and provide new insights into whether providing people with genetic-based lifestyle advice results in improvements in dietary intake, weight and body fat. To study this, we randomly assigned people to receive either standard advice for weight management or genetic-based advice for weight management and then followed up with them after 3, 6 and 12 months. The study participants also participated in a 12-month intervention. Overall, people who received the genetic-based advice experienced a decrease in body fat, more so than the people who received the standard advice after 3 and 6 months. After 12 months, there was no major difference in body fat between these two groups. When we looked at changes to their nutritional intake, people who received the genetic-based advice significantly reduced their overall intake of dietary fat after 12 months, whereas those who received the standard advice did not. Additionally, after 12 months, people who received the genetic-based advice better adhered to the recommendations for total fat and saturated fat compared to those who received the standard intervention. Overall, we found that nutrigenomics interventions can motivate long-term (12-month) dietary changes and can lead to improvements in body fat over the short-term (3-month) and moderate-term (6-month) to a greater extent than standard advice. Previous research shows that over time, the body tries to compensate for weight loss with physiological mechanisms promoting weight regain. This may help to explain why we found that after 12 months, the group receiving the standard advice had lost a similar amount of body fat as the group receiving genetic-based advice, despite the genetic intervention group improving their diet to a greater extent.