Dietary AAA/BCAA ratio and glycemic load are associated with obesity and novel anthropometric indices in Iranian adults

Obesity remains a major public health issue in Iran, with adult prevalence of overweight ~ 35–38% and obesity ~ 17–22%, driven by dietary transitions toward energy-dense, low-quality foods. While macronutrient quantity has been linked to obesity, the independent role of quality and its relation to novel anthropometric indices is underexplored in Iranian populations. This cross-sectional analysis used baseline data from the first phase of the PERSIAN Organizational Cohort Study at Mashhad University of Medical Sciences. Dietary intake was assessed using a validated 130-item semi-quantitative FFQ; Macronutrient quantity was expressed as percentage of total energy. Macronutrient quality indices were calculated (GI, GL, CQI for carbohydrates, AAA/BCAA, PAR for proteins, MUFA/PUFA, SFA/PUFA, PUFA/SFA for fats). BMI, ABSI, BRI, AVI and VAI were subsequently calculated from anthropometric measurements. Associations were evaluated using crude and multivariable-adjusted logistic regression, controlling for age, sex, physical activity, socioeconomic status, and total energy intake. A higher dietary AAA/BCAA ratio was consistently associated with lower odds of obesity and high levels of BRI and AVI after multivariable adjustment. Associations of glycemic index and glycemic load with adiposity outcomes were less consistent and attenuated after adjustment. Fat-quality ratios and the PAR showed no significant associations. Among the anthropometric indices examined, associations with dietary composition were observed most consistently for BRI and AVI. In this cross-sectional analysis of Iranian adults, a higher dietary AAA/BCAA ratio was associated with lower odds of obesity and selected novel anthropometric indices. Associations of glycemic load and glycemic index were less consistent. Longitudinal studies are required to establish temporality and potential causality.