BackgroundDietary intake and body weight are important predictors of long-term health. However, few studies have focused on these topics in adults with genetic syndromes that have associated intellectual disability, such as Williams syndrome (WS).ObjectiveIn adults with WS, describe predicted dietary intake, food-related problems, and associations between body mass index (BMI) and possible factors contributing to differences in weight status.DesignIn this study of 82 participants (median age of 30 years, range 18–69), we cross sectionally investigated associations between BMI, predicted dietary intakes (Dietary Screener Questionnaire), food-related behaviors (Food-Related Problem Questionnaire), and anxiety (Spence Children’s Anxiety Scale). Longitudinal patterns of weight change were further studied in a subset (n= 41).ResultsBMI variation was observed with median BMI of 27.3 kg/m2(range 16.7–55.5 kg/m2). Several components of dietary intake deviated from recommendations in the WS cohort. When compared with WS participants with either normal or overweight BMI, WS participants with obesity had reduced daily intake of fruits and vegetables of 0.15 cup equivalents (P= 0.049), while participants with underweight BMI had reduced daily intake of fruits and vegetables of 0.44 cup equivalents (P= 0.026) and additionally had reduced intake of dietary fiber of 2.12 grams per day (P= 0.019). A one-point increase in the ‘preoccupation with food’ sub-score was associated with a 0.57 unit increase in BMI (P= 0.16), while a one-point increase in the ‘takes and stores food’ sub-score was associated with a 0.72 unit increase in BMI. In the longitudinal weight subset, a weight gain group and a weight stable group were identified. The former was associated with increased ‘takes and stores food’ sub-score but not with dietary intakes.ConclusionWe observed considerable BMI variability. While few dietary intakes were associated with BMI, increased BMI and weight gain were associated with ‘preoccupation with food’ and with ‘takes and stores food’ behavior sub-scores.