She is an internal medicine physician practicing in the field of bariatrics. Lewis's research focuses on developing and evaluating interventions for obesity and related comorbidities. This work ranges from comparative effectiveness studies of bariatric surgical procedures, to trials of novel behavioral interventions for diet, to studies of policy interventions for improving diet at the population-level. Lewis currently serves as chair for the Health Services Research Section of the Obesity Society, and chair of the Obesity, Diabetes and Nutrition-Related Diseases working group for the Sackler Institute for Nutrition Science.