Lifestyle interventions are recommended for weight loss, but results are variable between different research evaluations. There is limited evidence on the influence of interventionist characteristics on participant weight loss. This study examined associations between interventionists, interventionist characteristics and participant weight loss during a structured lifestyle intervention.


Linear mixed models were used to evaluate interventionist predictors of weight loss in 415 adults participating in an 11-week commercial group weight loss program across 58 closed groups led by 11 interventionists. The intervention included diet, activity and behavior therapy components, and all interventionists received the same training.


Mean weight loss was 7.3% (range: -3.1% to 16.2%). There was a significant association between interventionists and participant weight loss (p=0.003), and adjusted means for individual interventionists ranged from 6.0% to 9.0%. Weight loss was greater for participants who had interventionists with a graduate degree in nutrition compared to a graduate degree in psychology (8.3% versus 6.4%, p=0.05).


These results suggest a relatively large effect of the interventionist and educational background on the weight loss of participants in structured lifestyle interventions.