**Background:** Diet quality in childhood is a major public health concern, as poor diets increase risks of undernutrition, obesity, and chronic disease. The Mediterranean diet (MedDiet) is a high-quality dietary pattern associated with numerous health benefits. Breastfeeding has been linked to better diet quality in children, including higher fruit/vegetable intake and lower ultra-processed food consumption, but whether breastfeeding is associated with adherence to a global dietary pattern like the MedDiet had not been previously assessed. This study aimed to analyze the association between breastfeeding history and adherence to the MedDiet in Spanish preschoolers.
**Methods:** Data were drawn from the SENDO (Seguimiento del Niño para un Desarrollo Óptimo) project, an ongoing Spanish pediatric prospective cohort. The analysis included 941 children (mean age 5.01 years, SD 0.85; 51% male) recruited between January 2015 and June 2022 with complete data on study variables. Breastfeeding history (type and duration) was retrospectively reported by parents via baseline questionnaires and categorized as never breastfed (n=150), breastfed <6 months (n=279), or breastfed ≥6 months (n=512). Adherence to the MedDiet was assessed using the KIDMED index (Mediterranean Diet Quality Index for Children), a 16-item score ranging from −3 to 12 points, with categories of poor (≤3), medium (4–7), or high (≥8) adherence. Covariates included child sex, age, race, screen time, physical activity, BMI z-score, gestational age, delivery method, birth weight, maternal age, maternal education, parental nutrition knowledge, and parental eating attitudes. Generalized mixed models accounting for intracluster correlation among siblings were used. Three progressively adjusted models were computed, and marginal effects were calculated.
**Key Results:** Overall, 84.1% of participants had been breastfed, and 54.4% were breastfed for ≥6 months. The mean KIDMED score was 5.5 in never-breastfed children, 5.7 in those breastfed <6 months, and 6.4 in those breastfed ≥6 months. Proportions with high MedDiet adherence (KIDMED ≥8) were 11.9%, 20.2%, and 26.6%, respectively. In the fully adjusted model (Model 3), children breastfed ≥6 months had a significantly higher KIDMED score compared to never-breastfed children (mean difference +0.93 points, 95% CI 0.52 to 1.34; p<0.001). The odds of high MedDiet adherence were nearly threefold higher for children breastfed ≥6 months (OR 2.94, 95% CI 1.50 to 5.36; p<0.01) after adjusting for all covariates including child demographics, perinatal factors, maternal characteristics, and parental nutrition knowledge and attitudes. A significant linear trend was observed across breastfeeding categories (p for trend <0.01). The marginal effect analysis showed 9.8% (95% CI 3.1% to 16.3%; p=0.04) more children with moderate-high MedDiet adherence in the ≥6 months breastfeeding group compared to never-breastfed. Breastfeeding <6 months showed non-significant positive associations.
**Clinical Implications:** This study provides novel evidence that breastfeeding, particularly for ≥6 months, is independently associated with higher adherence to the Mediterranean diet in preschool-aged children. The association persisted after extensive adjustment for sociodemographic, perinatal, and parental factors, suggesting breastfeeding may be an independent predictor of healthier dietary patterns. These findings reinforce WHO recommendations for exclusive breastfeeding through 6 months and highlight early-life nutrition as a critical window for establishing long-term healthy eating habits. Pediatricians and public health professionals should actively promote breastfeeding, especially in populations at higher risk (e.g., preterm or cesarean-delivered infants). Limitations include retrospective self-reporting of breastfeeding (though validation showed 96.8% agreement), a non-representative sample of predominantly white, highly educated families, and the cross-sectional design precluding causal inference. Prospective studies are needed to confirm causality and explore mechanisms, including gut microbiota influences and early flavor exposure.