We investigate the role of heterogeneous peer effects in encouraging healthy and sustainable lifestyles. Our analysis revolves around one of the largest and most extensive databases about weight loss, which contains well over 10 million observations that track individual participants' meeting attendance and progress in a large national weight loss program. A few key findings emerge. First, while higher weight loss among average performing peers leads to lower future weight loss for an individual, the effect of the top weight loss performer among peers leads to greater future weight loss for that same individual. Second, the discouraging effects from average peers and encouraging effects from top performing peers are magnified for individuals who struggled with weight loss in the past. Third, the encouraging effect of top performers has a long-run impact on an individual's weight loss success. Finally, we provide suggestive evidence that the discrepancy between the top and average performer effects is not likely an artifact of salience or informativeness of top performers, but instead, driven by its positive impact on the motivation to accomplish weight loss goals. Given our empirical findings, we discuss managerial implications on meeting design.