Participants were adults aged 18-74 years with a body mass index (BMI) >18.5kg/m² who subscribed to the standard Web-based weight loss program for at least the minimum subscription length of 12 weeks from June 27, 2011, to October 24, 2011, or the 8-week “challenge” version of the program, which began October 24, 2011. The subscription must have been the participants’ first for the commercial program, and those who did not pay for their subscription (eg, free promotional program trials) were excluded. The cost of a subscription in 2011 was AU$149 for SC. For BLC, the cost ranged from AU$19.95 per month if paid upfront for 12 months to AU$49.95 per month if paid monthly.

The commercial Web-based weight loss program was managed by SP Health Co, Australia. The standard program was The Biggest Loser Club (BLC) [9]. The short-term efficacy of the standard program, which is underpinned by social cognitive theory, incorporates key components of effective behavioral weight loss interventions, and includes persuasive features (Table 1), has been previously demonstrated [10]. The challenge version of the program was the Shannan Ponton Fast Track 8-Week Challenge (SC). Key program components are summarized in Table 1 and in Multimedia Appendices 1-4. SC included all features of BLC. However, to facilitate greater participant engagement SC drew on persuasive system design by offering enhanced system credibility support through the use of a celebrity personal trainer to endorse the program and host additional opportunities for social support. The celebrity personal trainer was Shannan Ponton, who is a qualified personal trainer on a national television program, “The Biggest Loser Australia”. The SC also used more “challenging” energy intake and expenditure targets (Table 1), with the goal of achieving greater initial weight loss.

SP Health Co collected the data that were provided to the researchers in a de-identified form. Ethics approval for the study was obtained from the University of Newcastle Human Research Ethics Committee, NSW, Australia.

Participants’ pretreatment demographic (sex, age, and ethnicity) and anthropometric characteristics (weight and height) were captured from an enrollment survey. Participants’ self-reported height and weight were used to calculate BMI (weight in kilograms divided by height in meters squared), which was categorized as healthy (BMI 18.5-24.9 kg/m²), overweight (BMI 25-29.9 kg/m²), or obese (BMI ≥30 kg/m²).

Participants self-reported weights (in kilograms) recorded online weekly were used to determine weight change achieved after 8 weeks. Two types of attrition rates were calculated: dropout and nonusage [11]. Dropout attrition rates were calculated based on the number of participants who did not complete the program and therefore included participants who cancelled their subscription prior to completing 8 weeks. Nonusage attrition rates were calculated based on the number of participants who did not drop out but stopped using all Web-based features and did not resume use within the 8 weeks. To describe website use, we calculated the number of participants who accessed each website feature (overall access, food diary entries, exercise diary entries, forum views and posts, menu plan, exercise plan, weekly educational materials, and live webinars attended) and the total number of days each feature was used.

Data analysis was undertaken using Stata 11.0 (StataCorp). Basic descriptive statistics were used to describe the baseline characteristics and website usage data. Differences between the two programs were tested using chi-square test for categorical data, t tests if normally distributed continuous data, or Wilcoxon Rank Sum test if non-normal continuous data. To determine the weight change achieved from enrollment to 8 weeks, generalized linear mixed models (GLMM) were utilized containing available self-reported weight records for all participants. Baseline age and sex were controlled for in the analyses as potential confounders. A secondary sensitivity analysis was conducted to determine the robustness of the results from the GLMM approach, by imputing missing 8-week weight data using the last observation carried forward (LOCF) method. A linear regression model was fitted with weight at 8 weeks as the outcome variable, group as the predictor variable, and enrollment weight, age, and sex as covariates.

Overall the study included 1334 individuals (953 BLC, 381 SC). Participants were predominantly female (86%), with an average age of 36.7±10.3 years, and half were of Anglo-Saxon descent (Table 2). At enrollment, SC participants had a lower mean BMI (30.6 vs 33.0 kg/m², P<.001) than BLC participants.

In total, 19 participants (1.4%) dropped out during the 8-week period with no significant difference in dropout rates between the two programs, but a possible trend of higher dropout rates among BLC participants: BLC 17 (1.8%) vs SC 2 (0.5%), P=.08. Nonusage attrition rates were 49.7% (n=653/1315) at 8 weeks. There was no significant difference in nonusage attrition rates between programs (P=.47) as 51.2% of BLC (480/936) and 48.8% of SC (185/379) participants stopped using all website features during the 8 weeks and did not return to use.

The primary analysis using GLMM resulted in a mean self-reported weight reduction of −4.6 kg (95% CI −4.9 to −4.4 kg) or −5.3% for all participants. SC participants self-reported significantly greater weight loss (–5.1 kg [–5.5 to –4.6 kg] or –6.0%) than BLC participants (–4.5kg [–4.8, –4.2] or –5.0%) after 8 weeks (P=.03) with small effect sizes (0.06 and 0.14 respectively).

The sensitivity analysis using LOCF gave a mean self-reported weight loss of −2.7 kg (−2.9 to −2.6 kg) or −3.0% after 8 weeks for all participants. SC participants self-reported significantly greater weight loss (–3.0 kg [–3.3 to –2.6kg] or –3.4%) than BLC participants (–2.6 kg [–2.9 to –2.4 kg] or –2.9%) after 8 weeks (P<.001), with small effect sizes (0.09 and 0.15 respectively). A significantly higher proportion of SC participants self-reported a weight loss of ≥5% after 8 weeks than the BLC participants (27.3% vs 22.6%, P=.02). See Table 3.

Website use for SC and BLC participants is described in Table 4. SC participants accessed and posted to the discussion form, viewed the program plan, menu plans, exercise plans, and educational materials more than BLC participants (Table 4). BLC participants made a significantly greater number of food entries and used the online diary on significantly more days than SC participants (Table 4). There were no significant differences in the number of weekly weigh-ins recorded or the number of exercise entries in the online diary between the two programs.

The primary aim of this study was to determine whether an 8-week challenge version of a commercial Web-based weight loss program, which integrated persuasive features including system credibility support through the use of a celebrity personal trainer to endorse the program and host additional opportunities for social support, demonstrated greater initial weight loss and program engagement compared to the standard program. In the current study, the 8-week challenge version facilitated greater weight loss and engagement, but dropout and nonusage attrition rates were comparable to the standard program.

The true weight loss achieved by participants is likely to be in the range between the GLMM and LOCF results, that is, -3.4% to -6.0% for the SC and -2.9% to -5.0% for BLC, due to reasons previously described [12]. At the group level, the difference in weight loss between the groups was statistically different, but the effect size was small, suggesting that the difference between the two groups weight loss may not be clinically significant. Although there was no significant difference in attrition rates between the two programs, there was a trend for lower dropout attrition for SC participants. Furthermore, frequency of use of the website was superior for SC participants, and they were more likely to use some website components. SC participants engaged more with the standard social support components (eg, discussion forum) SC participants were also more likely to access educational materials than BLC.

The differences in initial weight loss and engagement between the BLC and SC programs could be partly explained by the inclusion of additional persuasive features. By offering more opportunities for social support to SC participants, a more supportive environment may have been created [13]. The support environment may have allowed SC participants to compare their performance to others (social comparison) or motivated participants to change their behavior if they recognized that other participants were successfully making change (social facilitation). Furthermore, the use of a celebrity personal trainer to endorse and provide content within the SC program may have been more persuasive by boosting the perceived credibility of the program. Alternatively, the differences in weight loss and engagement may be due to the more stringent energy intake and expenditure targets set as part of the SC program. For example, greater access to the educational materials may have been required to facilitate adherence with the targets, suggesting that these resources may be necessary to facilitate adherence to the energy intake and expenditure targets set as part of SC program. However, as compliance to the recommended energy intake and expenditure targets for each program were not measured and an observational study design was used, we cannot be sure which components of SC lead to greater engagement and weight loss (ie, the persuasive features of social support and/or system credibility support, or different energy expenditure and intake goals).This could be examined in future studies.

The weight loss analysis used participants’ weigh-in records self-reported online. However, the accuracy of weight self-reported on the Internet has been shown to be reasonable [14]. Outcomes were evaluated only during the 8-week challenge; therefore, the long-term impact on user engagement and weight loss were not considered. As the SC program was more expensive for participants to subscribe to than the BLC program, future studies should also consider the cost-effectiveness of the programs when evaluating program effectiveness. Finally, the use of a celebrity personal trainer also limits the external validity of the results.

This preliminary observational study supports the need for further evaluation of Web-based weight loss programs that incorporate persuasive strategies, including enhanced credibility support and social support, to enhance initial weight loss and engagement. Future randomized control trials accompanied by mediation analyses should specifically determine which intervention components (ie, persuasive features: social support and/or celebrity endorsement, or stringent eating and physical activity recommendations) of the Web-based program are associated with improvements in engagement and weight loss, and whether initial weight loss and engagement are maintained in the long term.