A large-scale observational analysis of social media data reveals major public misperception of the attainability of drastic weight loss by dieting

Introduction: Diet forums in social media websites provide an opportunity to glimpse the experience of different weight loss diet strategies reported by tens of thousands of individuals. 
Methods: We analyzed all postings with weight information from the six major Reddit weight-loss diet forums (“subreddits”) as reported by forum participants. 
Results: Data were collected from January 2011 to April 2020 from all 55,900 users posting weight information. Average start BMI was in the overweight or obese range (26–34 kg/m2), and average goal BMI was in the normal range (21.5–24.5 kg/m2) for all subreddits. There is correlation between start BMI and goal BMI (R2=0.63, p<10-10) and between planned weight loss and reported weight loss (R2=0.56, p<10-10). Approximately 80% of forum participants reported a weight loss that was greater than 5% of their initial body weight. Actual reported weight loss was less than half of goal weight loss. Average reported weight loss and adherence were highest in the keto and loseit subreddits. More upvotes and fewer downvotes were associated with higher reported weight loss in five of the six subreddits. 
Conclusions: Despite the need for cautious interpretation of this data due to self-selection of users who updated weight loss and the possibility of unreliable weight reports, the study has several findings. Average goal BMI was in the normal weight range, demonstrating a highly unrealistic perception, in a very large lay-public cohort, of the plausibility of losing all excess weight. The success in weight loss and maintenance in self-selected individuals who continued reporting weight for many months may demonstrate the subjective value some individuals can obtain from forum participation.