Different categories of soy products and metabolic dysfunction-associated steatotic liver disease in cross-sectional study of NHANES 2007-2020.

Although numerous studies have investigated the relationship between soy products and metabolic dysfunction-associated steatotic liver disease (MASLD), the findings have been highly inconsistent. A fundamental reason for this is that prior research has predominantly treated "soy products" as a single, homogeneous exposure variable, overlooking substantial heterogeneity arising from differences in processing methods, consumption purposes, and regional dietary patterns. This study seeks to address this methodological limitation by developing a fine-grained classification framework, which for the first time enables a systematic investigation into the potentially heterogeneous associations between distinct categories of soy products and MASLD in the U.S. population: an epidemiological context marked by low overall soy intake and a predominance of processed soy foods. Using National Health and Nutrition Examination Survey data, this study developed a classification system of soy products based on processing characteristics and consumption purposes. The core analytical approach employed was weighted multivariable logistic regression, which was complemented by subgroup and mediation analyses to comprehensively investigate intercategory differences in these associations. Sensitivity analyses were additionally performed to verify the robustness of the study findings. In a nationally representative U.S. population, different categories of soy products showed heterogeneous associations with MASLD. Future studies need to apply fine-grained classifications based on processing methods and consumption purposes, and explicitly account for population heterogeneity across demographic and lifestyle characteristics. After full adjustment for confounders, only traditional fermented soy products and soy-based functional snacks had significant inverse associations with MASLD, while no consistent links were found for other categories (traditional non-fermented soy products, soy-based meat alternatives, soy protein supplements, foods with soy additives). Mediation analyses additionally revealed that these categories were inversely associated with the outcome, and differed in their mediation patterns; Subgroup analyses showed the strength of these associations differed across population subgroups.