A Single-Food Substitution Strategy (SFSS) Improves Fat Mass and Metabolic Parameters in MASLD: A Prospective Pilot...

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD) is associated with obesity, insulin resistance, and altered body composition. Although dietary intervention is a cornerstone of treatment, complex or calorie-restricted regimens may reduce long-term adherence. This study evaluated the effects of a pragmatic, short-term intervention that involved replacing one daily carbohydrate serving with cruciferous vegetables on body composition and metabolic parameters in individuals with obesity and MASLD. Associations between changes in fat mass and vitamin D and follistatin levels were also explored. Methods: In this prospective pilot study, 44 adults with obesity and MASLD followed a two-month intervention, substituting one daily serving of carbohydrate-rich foods with 200 g of cruciferous vegetables, without prescribed caloric restriction. Anthropometric, bioimpedance, biochemical, and FibroScan assessments were performed at baseline and post-intervention. Changes were analyzed using the Wilcoxon signed-rank test, Spearman's correlation analysis, and generalized estimating equation (GEE) models adjusted for confounding factors. Results: The intervention was associated with a significant reduction in fat mass (-4.86 kg, p < 0.001), corresponding to an average relative decrease of approximately 12% along with improvements in metabolic and hepatic parameters. Changes in fat mass were inversely correlated with changes in vitamin D (rho = -0.33, p = 0.035), fat-free mass (rho = -0.37, p = 0.018), and follistatin (rho = -0.24, p = 0.143). In multivariate GEE models, the intervention remained independently associated with fat mass reduction (β = -5.190, p < 0.001). Conclusions: A simple carbohydrate-to-vegetable substitution without prescribed caloric restriction was associated with improvements in body composition and metabolic health. These exploratory findings suggest that pragmatic dietary modifications may provide clinically meaningful metabolic benefits and support the feasibility of minimal dietary substitution strategies in this population. However, causal inferences remain limited by a single-arm pilot design and require confirmation in larger randomized controlled trials.