Assessing Bone and Adipose Tissue Biomarkers in 5–6-Year-Old Polish Children Adhering to Vegetarian and Traditional Diets

Background/Objectives: Plant-based diets are increasingly adopted by families with young children, yet their potential effects on bone development and metabolic regulation during early childhood remain insufficiently understood. This study aimed to evaluate body composition, bone mineral density (BMD), biochemical markers of bone turnover, and adipokine profiles in healthy children aged 5–6 years adhering to lacto-ovo-vegetarian or omnivorous diets. Methods: A cross-sectional analysis was conducted in a well-characterized cohort of 90 healthy normal-weight children consuming either lacto-ovo-vegetarian or omnivorous diets. Body composition and bone mineral density were measured using dual-energy X-ray absorptiometry, and circulating markers of bone formation, resorption, and adipokines were determined using ELISA methods. Correlation analyses were performed to examine the relationships between anthropometric variables, bone parameters, and adipokines. Results: No significant differences were observed between vegetarian and omnivorous diets in anthropometric characteristics, bone mineral content (BMC), or BMD, indicating comparable skeletal status. However, vegetarian children exhibited significantly higher levels of bone turnover markers, including bone alkaline phosphatase (BALP) (p = 0.023) and C-terminal telopeptide of type I collagen (CTX-I) (p = 0.035), and a lower osteocalcin OC/CTX-I ratio (p = 0.027). These findings may suggest a subtle imbalance in bone remodeling dynamics in these children, although their clinical significance remains uncertain. Additionally, higher levels of carboxylated osteocalcin (Gla-OC) (p = 0.022) and an increased carboxylated to undercarboxylated OC (Gla-OC/Glu-OC) ratio (p = 0.005) were observed in vegetarian children. Among adipokines, vegetarian children showed lower HMW adiponectin levels (p = 0.05) and a lower HMW/total adiponectin ratio (p = 0.012). Correlation analyses revealed distinct metabolic patterns between groups. In vegetarian children, bone parameters were primarily associated with lean mass, indicating the predominant role of mechanical factors in skeletal development. In contrast, omnivorous children demonstrated a more integrated relationship between bone indices and adipokines. Conclusions: In conclusion, while a lacto-ovo-vegetarian balanced diet supports normal bone mass in early childhood, it may be associated with subtle alterations in bone metabolism and its regulatory pathways, including adipokine profiles. These findings highlight the importance of adequate dietary planning and underscore the need for longitudinal studies to determine long-term effects on bone status.