Thomas A. Wadden (born September 3, 1952) is a clinical psychologist and educator who is known for his research on the treatment of obesity by methods that include lifestyle modification, pharmacotherapy, and bariatric surgery.

[5] In 1982, Wadden was appointed to the faculty in the Department of Psychiatry at the University of Pennsylvania, where he began his clinical and research career on the treatment of obesity and its associated eating disorders.

Wadden's early contributions to the management of obesity included the first controlled, long-term trial of high protein, very low calorie diets (<800 kcal/d) and the documentation of the marked weight regain with this approach.

[13] This work resulted in Congressional testimony and in a collaboration with the Federal Trade Commission, other researchers, and members of the weight loss industry to improve information provided to prospective dieters.

[14] With colleagues from the Look AHEAD Research Group, he demonstrated that patients with obesity and type 2 diabetes who lost approximately 8% of initial weight with an intensive lifestyle intervention experienced long-term improvements in cardiovascular risk factors, quality of life, and medical care costs.

[16] With Gary Foster, Wadden also developed the Weight and Lifestyle Inventory (WALI), which is widely used to assess the behavioral and psychosocial status of candidates for bariatric surgery.