Obesity in young adult Americans rose from 33% to 41% over the timeframe of the study.M. Spencer Green/AP Diabetes and obesity two risk factors for heart disease are on the rise among young adults in the U.S., according to a newly published study of about 13,000 people ages 20 to 44 years old.The prevalence of diabetes climbed from 3% to 4.1%; obesity shot up from 32.7% to 40.9%, based on the study, published in the Journal of the American Medical Association on Sunday, which uses data from 2009 to 2020.