Behavior modification programs aimed at changing diet and physical activity have been shown to be an effective weight loss approach (1). The most effective among these has been the one-on-one Diabetes Prevention Program (DDP) (2) for which clinically significant weight loss of 5-7% and a reduction in diabetes by 58% compared to placebo has been found at an average three years post-intervention (3). Participants in this program displayed modest weight regain (e.g., 2.2lbs); however, diabetes incidence remained lower at 10-year follow-up (4).
Due to the high cost of the DPP, a group-based shortened version, called the Group Lifestyle Balance (GLB) program, was developed (5). While less costly to implement and thus more accessible, its effectiveness is lower than the DPP. A recent meta-analysis showed that weight loss with the GLB was 3.99% at post-intervention compared to 7% with the DPP (6). One of the few GLB intervention studies that provide longer term weight loss maintenance data found that the probability of achieving a 5% weight loss at 3 months was 45.7% (it is unclear why the results were reported as probabilities and not actual percentages of weight loss), but only 17.3% of participants maintained this weight loss one year post-intervention (7). Also, of those who lost at least 5% of their body weight post-intervention, 52.6% maintained it at 24 months, weighing about 20lbs less than at baseline (7).
To increase the weight maintenance effectiveness of the GLB, our study integrated habit formation techniques, specifically if-then plans, to reinforce habit change (8,9). This group was called the enriched GLB or the McGill Comprehensive Health Improvement Program (CHIP) Healthy Weight Program as it was conducted with the McGill CHIP which is a multidisciplinary disease management and prevention program that is the primary site of academic research and teaching activities on exercise and health for the McGill medical community. If-then plans (also called implementation intentions) are concrete contingency plans that specify when, where, and how to act in a specific situation (8,9). If-then plans have demonstrated medium to large effects in inducing habit change in a number of behaviors (10). However, not many long-term studies of implementation intentions and complex behaviors yet exist.
The GLB standard and enriched versions were delivered over one year (12 weekly core sessions, 4 transitional sessions over 3 months, and 6 monthly support sessions). The 3- (end of core sessions) and 12- (end of intervention) months results of the if-then enhanced randomized controlled trial (RCT) have been published (11). No between-group differences were found, i.e. there appeared to be no added benefit to augmenting the GLB (control group) with the if-then plans (enriched GLB group). However, both groups displayed large weight losses of 9.98% over 12 months. One of the reasons hypothesized for the lack of significant group differences was that participants in both conditions were trained to become more aware of their internal and external cues and to create responses to these cues. As a consequence, the creation of if-then plans might have also occurred in the standard GLB group participants, just more implicitly. Also, the coaches in both groups were highly trained in cognitive behavioral therapy (CBT; 11) and spent two entire sessions teaching participants how to identify problematic cues and add positive food, physical activity, and social cues to their environment. It is possible that this behavioral training in addition to the therapeutic contact with the coaches that all participants received increased the overall effectiveness of the program but did not allow for much difference between the standard and enriched GLB groups.
This paper reports the findings of our RCT after a 1-year no-contact follow-up period or 24-months. We hypothesized that the if-then plans would serve as a protective barrier to weight regain. Specifically, we hypothesized that from the end of intervention (12 months) to follow-up (24 months), the if-then plan group would show greater weight loss maintenance than the group that was not explicitly instructed to create if-then plans.