Abstract
<title>Abstract</title> <p>This cross-sectional study examined the independent associations of intact grain energy density and background non-grain ultra-processed food (UPF) share with measured waist circumference in a nationally representative sample of US adults, and tested whether those associations differed by biological sex. Most studies have not disaggregated grain-based from non-grain UPF exposure, nor formally tested sex as a modifier of the UPF-adiposity relationship. We analysed 5,183 adults aged 20 to 79 years from the National Health and Nutrition Examination Survey 2021 to 2023 cycle. Dietary exposures were derived from Day 1 24-hour dietary recalls using 8-digit USDA Food and Nutrient Database for Dietary Studies codes and expressed as isocaloric percentages of total daily energy intake. Complex survey linear regression models adjusted for age, sex, race and ethnicity, income-to-poverty ratio, and total energy intake. Background non-grain UPF share was independently and positively associated with waist circumference in the fully adjusted pooled model (β = 0.1453, SE = 0.0257, p = 0.005). Intact grain energy density showed no independent association in any model. The UPF association was significantly stronger in males (β = 0.1965, p = 0.003) than females (β = 0.0945, p = 0.020), confirmed by a formal sex interaction test (β = −0.1051, p = 0.048). Sensitivity analyses restricting intact grain classification to structurally preserved grain codes yielded identical estimates. These findings identify the broader dietary processing environment, rather than intact grain intake in isolation, as the dietary construct most consistently linked to abdominal adiposity.</p>