Assessment of Dietary Soy Isoflavones Intake Among Women Aged 14 Years and Older in China: A Population-Based Cross-Sectional Study

Objective: This study assessed dietary soy isoflavone (SIF) intake among Chinese women ≥14 years, identified determinants, and evaluated adequacy against the Specific Proposed Level (SPL) in Chinese Dietary Reference Intakes, to inform targeted guidance. Methods: Intake was estimated using a distribution model combining 2017–2020 China National Food Consumption Survey data with SIF concentrations from food composition tables. Demographic differences and adequacy versus age-specific SPL were examined; supplemental doses were calculated for individuals below SPL. Results: Mean SIF intake was 14.77 mg/standard person-day, generally low. Significant differences (p < 0.05) were observed across most demographic subgroups except education. Higher mean intakes (mg/day) were seen in women aged ≥65 years (16.20), rural residents (16.38), light activity level (15.17), annual income > 100,000 CNY (15.51), manual laborers (16.11), and central China residents (highest, 21.01). Dried legumes and products, particularly tofu and its derivatives, contributed about 80% of total intake, with tofu-derived items accounting for 57.62–71.49%. Across all age groups, intake was significantly below the SPL, with >96% of participants failing to meet the recommendation. To reach the SPL, premenopausal women require ~40 mg/day supplemental SIF (equivalent to ~45 g soybeans/products), while perimenopausal and postmenopausal women require ~60 mg/day (~60 g soybeans/products). Conclusions: Dietary SIF intake among Chinese women ≥14 years is substantially below the SPL, a deficit that may attenuate associated health benefits. As dried beans and bean products are the dominant contributors, promoting these foods represents a feasible strategy to improve population-level SIF adequacy.