Discussion
loss of fat-free mass, muscle mass, weight loss, fat-free mass
The main finding of this study was that the interactive web-based health program focusing on dietary energy density showed positive effects on body weight, fat mass, and waist circumference. These effects were significantly more pronounced in the intervention group than in the control group with only web-based knowledge transfer and were also evident in the longer-term 12-month follow-up period. With regard to short-term weight loss from web-based interventions (3-4 months), comparable interventions reported short-term weight loss of 2.0 kg [Fat mass in the intervention group decreased significantly compared with the finding in the control group over the course of the study, whereas fat-free mass reduced in the intervention group, but did not differ between the 2 groups. Both of these are important findings because few web-based interventions perform body composition measurements and most use self-reported parameters. This limits the accuracy of the measurements and does not provide direct information regarding the loss of body fat. Moreover, it is known that weight loss interventions can result in a loss of fat-free mass and muscle mass [The effectiveness of the interactive web-based health program was also partially evident in behavioral variables, such as energy density, energy intake, fat intake, and self-reported physical activity. Based on the focus of the program, the reduction in energy density in the short and long term in the intervention group was an important finding. Energy intake developed consistently with energy density in the intervention group, although the effect was significant only in the short term. The increase in energy density at t2 in both groups could be due to a seasonal effect [Despite the positive effects on body weight and composition, the improvements in cardiometabolic variables in the intervention group were small and not significantly superior to the findings in the control group. For some variables, such as systolic and diastolic blood pressure, improvements were similar to those with other web-based interventions, whereas LDL cholesterol showed a worse trend [The results of this study confirm the benefits of lowering energy density shown by several previous studies in relation to weight loss [Several limitations must be considered in this study. First, complete blinding was not possible due to the recognition of the program by the participants. Therefore, the motivation of the participants might have been influenced based on the recognition of the program. Second, both study groups might have been additionally motivated to attain their health goals by interest in free medical examinations as well as activity trackers received as incentives. Conversely, the participants of the clinical substudy might have been more motivated than the participants of the online study already at the beginning, since participation in medical examinations required more commitment. Third, the effect of the COVID-19 pandemic on both groups was difficult to quantify. Qualitative feedback from study participants indicated that the COVID-19 pandemic and its associated restrictions affected people positively, negatively, or not at all with regard to their weight management, dietary, or physical activity behaviors. Descriptive examinations of physical activity during the first lockdown in March 2020 showed, on average, negligible change in measured physical activity. Fourth, nonuse might have affected the effectiveness of the program and the study results. Overall, however, the usage analysis showed that the program was used multiple times by all participants in the intervention group of this study (data not shown). Because the control group received only web-based information without updates, one-time use was expected. However, despite these limitations, this study provides evidence that an interactive and fully automated web-based health program focusing on energy density concepts exerts positive effects on weight loss among people with overweight and obesity. The standardized measurement of body weight and clinical variables in this study, compared with the self-reported measurement of body weight in other studies, is a strength of this study. Owing to the potentially unlimited availability of fully automated web-based programs, there may be relevant public health effects.This clinical study showed that an interactive web-based weight loss program was effective and superior to a noninteractive web-based weight loss program. The interactivity of web-based interventions seems to play an important role in effectiveness. Based on the present results, pure knowledge transfer is not sufficient to induce sustainable weight loss and adherence to a diet with low energy density. In the web-based intervention studied here, interactivity was established via feedback on dietary documentation and activities achieved or not achieved. Future research should consider in more detail what and how much interactivity is necessary to make web-based weight loss interventions effective. Nevertheless, our results suggest that integrating the concept of a diet with low energy density into an interactive web-based weight loss program is useful for achieving weight loss.The project was funded by Techniker Krankenkasse (German Health Insurance Company). The project funder had no influence on the planning and implementation of the study, the analysis and interpretation of the data, or the publication of the results. We thank all study participants in the clinical weight loss trial as well as all study staff who made the implementation possible. In addition, we would like to thank Techniker Krankenkasse, represented by Nicole Knaack, Kerstin Hofreuter-Gätgens, and Dagmar Köppel, for funding this study. Additionally, we would like to thank Irina Kopman and her team at Vilua Healthcare GmbH for IT support. We also acknowledge support by the Open Access Publication Fund of the University of Freiburg.Authors' Contributions: JK, JB, RW, RF, MS, IT, PM, UAF, CA, EFG, AG, and DK contributed to the conception and design of the study and methodology. JK, JB, and DK were in charge of the project administration. JK, JB, CC, and MS performed the statistical analysis. JK wrote the first draft of the manuscript. All authors contributed to the manuscript revision, and read and approved the submitted version.Conflicts of Interest: The Department of Sport and Sport Science (JK, JB, RW, DK, and RF) and Section for Health Services Research and Rehabilitation Research (SEVERA) (MS, IT, EFG, CA, UAF, and PM) were commissioned by Techniker Krankenkasse (German Health Insurance Company) for the scientific evaluation of the web-based health program. JK, JB, and DK report funding from Techniker Krankenkasse for clinical trial design, implementation, and scientific evaluation. CC and AG declare that they have no conflicts of interest. RW, RF, MS, IT, EFG, CA, UAF, and PM report funding from Techniker Krankenkasse for the design, implementation, and scientific evaluation of the online trial.Effect sizes of anthropometric variables (intention-to-treat analysis).Results of the robust linear mixed model of behavioral variables (intention-to-treat analysis).Effect sizes of behavior variables (intention-to-treat analysis).Effect sizes of cardiometabolic variables (intention-to-treat analysis).Results of the robust linear mixed model of cardiometabolic variables (intention-to-treat analysis).CONSORT EHEALTH Checklist (V 1.6.1).