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

1. Introduction

In recent years, interest in plant-based nutrition has grown rapidly among adults and pediatric populations. Vegetarian diets, which exclude meat, and in some cases, other animal-derived products, are increasingly being adopted by families with young children for ethical, environmental, or perceived health-related reasons [1]. While numerous studies have demonstrated the potential health benefits of vegetarian dietary patterns in adults, such as reduced risks of obesity, cardiovascular disease, and type 2 diabetes, the implications of such diets during early childhood remain a subject of ongoing scientific debate [2,3,4,5].

Early childhood is a critical period of rapid growth and development, during which adequate nutrition is essential to support optimal growth, immune function, neurodevelopment, and metabolic programming [6]. Particularly concerning are processes related to bone metabolism and adipose tissue development, both of which are highly sensitive to dietary composition and nutrient availability. Bone accrual during this stage is fundamental for achieving optimal peak bone mass later in life, while adipose tissue plays a key role not only in energy storage but also in endocrine regulation and metabolic homeostasis [7,8].

Bone development is commonly assessed using bone mineral content (BMC) and bone mineral density (BMD), which are key indicators of bone strength and mineralization. The measurement of biochemical markers of bone metabolism, including osteocalcin (OC) and its carboxylated (Gla-OC) and undercarboxylated (Glu-OC) forms, bone-specific alkaline phosphatase (BALP), and C-terminal telopeptide of type I collagen (CTX-I), provides valuable insights into the dynamic processes of bone formation and resorption [9,10]. These markers may allow early detection of imbalances in bone metabolism, which can be influenced by dietary factors, particularly the intake of calcium, vitamin D, and protein.

The balance between bone formation and resorption is tightly regulated by complex molecular signaling pathways that control osteoblast and osteoclast activity. Among these, the RANK/RANKL/OPG (receptor activator of nuclear factor κB/receptor activator of nuclear factor κB ligand/osteoprotegerin) system and the Wnt-β-catenin signaling pathway (modulated by sclerostin) play central roles in the regulation of bone mass, osteoblast and osteoclast differentiation, and osteocyte function [11,12].

In parallel, increasing attention has been paid to the role of adipose tissue metabolism and its endocrine function in early life [8,13]. In parallel, increasing attention is being paid to the role of adipose tissue metabolism and endocrine function in early life. Adipose tissue secretes a range of bioactive molecules, known as adipokines, including leptin and adiponectin, which regulate appetite, insulin sensitivity, inflammation, and energy balance. Importantly, these adipokines influence bone metabolism, highlighting the existence of a functional interplay between adipose tissue and the skeletal system [7]. As such, adipokines may serve as valuable biomarkers reflecting early alterations in body composition and metabolic health shaped by dietary patterns.

A systematic review and meta-analysis of adult populations suggests that vegetarian and especially vegan diets, may be associated with lower BMD than omnivorous diets, particularly at clinically relevant skeletal sites such as the femoral neck and lumbar spine [14]. Furthermore, large prospective cohort studies have reported an increased risk of total and site-specific fractures, including hip fractures, among individuals following vegetarian diets compared with meat-eaters [15,16,17]. These findings are often attributed to differences in nutrient intake, particularly lower consumption of calcium, vitamin D, and high-quality protein.

Despite the growing prevalence of vegetarian diets among young children, there is a paucity of studies investigating their effects on bone health and metabolic regulation during early childhood. The available evidence suggests that vegetarian children may exhibit alterations in bone turnover markers, sometimes accompanied by slightly lower BMC and BMD compared with their omnivorous peers [18,19]. However, many studies include heterogeneous age groups or focus on older children, limiting the ability to draw conclusions specific to early childhood. Most studies either focus on older children or are not designed to assess the simultaneous influence of diet on both skeletal and adipose tissue metabolism.

While several pediatric and nutrition societies state that well-planned vegetarian diets can be appropriate for children if carefully managed and adequately supplemented, others have raised concerns regarding the potential risk of inadequate nutrient intake and long-term consequences for skeletal health [20,21,22,23,24].

Given these considerations, there is a clear need for comprehensive studies focusing on narrow and developmentally critical age groups. Therefore, the present study aimed to address these important gaps by evaluating anthropometric parameters, bone mineral density, bone metabolism markers, and circulating adipokines in healthy 5–6-year-old children adhering to either a vegetarian or traditional omnivorous diet. Additionally, the study explored the potential associations between anthropometric measures and biochemical markers, offering a more integrated understanding of bone and adipose tissue metabolism in young children following vegetarian and omnivorous diets.

2. Materials and Methods

2.1. Participants

The study included 90 healthy children aged 5–6 years. Participants' health status was evaluated through medical history and basic physical examination. All studied children were of normal weight and free from chronic diseases that could affect bone metabolism. They followed balanced diets that met their energy and macronutrient requirements, in accordance with the Polish dietary guidelines [25]. Among them, 50 children (26 boys and 24 girls) had been following a vegetarian diet since birth, specifically the lacto-ovo-vegetarian dietary pattern, that included milk, dairy and eggs. As described in a previous study [26], prepubertal children on a vegetarian diet had a lower protein intake, higher carbohydrate intake, and a comparable fat intake relative to omnivores. However, these values were still with the reference ranges.

The comparison group consisted of 40 children (20 boys and 20 girls) consuming a traditional omnivorous diet that included meat, poultry, and fish.

The exclusion criteria were low birth weight, developmental or nutritional disorders, gastrointestinal diseases, or regular use of medications, with the exception of standard vitamin D supplementation at a dose of 600–1000 IU/day (15–25 μg/day), as per the updated guidelines for preventing and treating vitamin D deficiency in Poland [27].

Participants were recruited between July 2022 and June 2025 at the Institute of Mother and Child in Warsaw, Poland.

The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of the Institute of Mother and Child in Warsaw, Poland (Protocol Code: 15/2022; Date of Approval: May 5, 2022). Written informed consent was obtained from the parents or legal guardians of all participants.

2.2. Anthropometric and Body Composition Measurements

All participants underwent comprehensive clinical evaluation and anthropometric assessment. Height and weight were measured using standardized equipment, and body mass index (BMI) was calculated as body weight (kg) divided by height squared (m²). BMI Z-scores were derived using age- and sex-specific Polish reference charts [28]. Body composition, total body less head bone mineral content (TBLH-BMC), and bone mineral density in the total body less head (TBLH-BMD) and BMD in the lumbar spine (L1–L4), were assessed using dual-energy X-ray absorptiometry (DXA) with a Lunar Prodigy scanner (General Electric Healthcare, Madison, WI, USA) with pediatric database enCORE software version 9.30.044. We used TBLH-BMD according to the Official Positions of the International Society for Clinical Densitometry 2013 [29].

2.3. Biochemical Analyses

Fasting venous blood samples were collected between 8:00 AM and 10:00 AM, centrifuged at 1000 ×g for 10 minutes at 4 °C to separate the serum, and stored at –80 °C until analysis. Serum levels of 25-hydroxyvitamin D – 25(OH)D were determined using the electrochemiluminescence method (ECLIA) with kits from DiaSorin Inc. (Stillwater, USA). Biochemical bone metabolism markers and adipokine concentrations were quantified using commercially available human enzyme-linked immunosorbent assay (ELISA) kits according to the manufacturers’ protocols.

Bone metabolism markers:

• Bone alkaline phosphatase activity was measured using the BAP EIA kit (Quidel, Athens, OH, USA), with detection limit of 0.7 U/L, and intra- and inter-assay coefficients of variation (CVs) below 5.8% and 7.6%, respectively.
• Osteocalcin and C-terminal telopeptide of type I collagen were assessed using N-MID Osteocalcin ELISA kits and Serum CrossLaps (CTX-I) ELISA kit (IDS, Bolton, UK). The limit of detection for OC was 0.5 ng/mL, intra- and inter-assay CVs were <2.2% and <5.1% and for CTX-I was 0.02 ng/mL, <3.0% and <10.9%, respectively.
• Carboxylated and undercarboxylated osteocalcin levels were measured using ELISA kits from Takara Bio Inc. (Shiga, Japan), with intra- and inter-assay CVs below 2.4% and 4.8% for Gla-OC and <6.7% and 9.9% for Glu-OC, respectively. The limit of detection was 0.25 ng/mL for both forms of osteocalcin.
• Osteoprotegerin was determined using kits from DRG Diagnostics (Marburg, Germany) with a limit of detection of 0.03 pmol/L, intra-assay CV< 4.9% and inter-assay CV <9.0%.
• Soluble receptor activator of nuclear factor kappa-B ligand were measured using the Human sRANKL ELISA kit from SunRed Biotechnology (Shanghai, China). The detection limit was 1.56 pg/mL; intra- and inter-assay CVs were <9% and <11%, respectively.
• Sclerostin was measured using the Sclerostin HS ELISA kit from Teco Medical Group (Sissach, Switzerland) with intra- and inter-assay CVs less than 4.8% and 8.2%, respectively, and a detection limit of 0.006 ng/mL.

Adipokines:

• Leptin levels were determined using ELISA kits from DRG Diagnostics (Marburg, Germany) with detection limit of 0.7 ng/mL, and intra- and inter-assay CVs below 5.9% and 8.6%, respectively.
• Total adiponectin and high-molecular-weight adiponectin were measured using ELISA kits from ALPCO Diagnostics (Salem, NH, USA). The limit of quantitation was 0.019 ng/mL, intra- and inter-assay CVs were <5.4% and <5.0% for total adiponectin, and <5.0% and <5.7% for HMW adiponectin, respectively.

Biochemical parameters were measured in all children, except for HMW adiponectin, which was analyzed in 49 (98%) vegetarian and 38 (95%) omnivorous subjects.

2.4. Statistical Analyses

Normality of the data distribution was assessed using the Kolmogorov–Smirnov test. Data are presented as mean ± standard deviation (SD) for normally distributed variables and as median with interquartile range (IQR; 25th–75th percentiles) for non-normally distributed variables. For selected parameters, the relative percentage difference between the vegetarian and omnivore groups was calculated by dividing the absolute difference by the value in the second group and multiplying by 100. The ratios of OC/CTX-I, Gla-OC/Glu-OC, OPG/sRANKL, leptin/total adiponectin, and HMW/total adiponectin were calculated.

Group differences in anthropometric, biochemical, and bone-related parameters were evaluated using the Mann–Whitney U test. Where a significant difference was found between the groups, the effect size (ES) was calculated by dividing the absolute value of the standardized Mann–Whitney U test statistic by the square root of the total sample size (N = 90). Correlation analyses were performed using Spearman’s rank correlation test.

In this type of study, the sample size is determined by patient availability; in our case, 5–6-year-old children who have followed a vegetarian diet since birth. We could only assess, in a statistical sense, the power of our study using a post hoc method. We conducted this analysis using the free G*Power (version 3.1.9.7) software, taking into account the type I error rate, group sizes, and effect size.

A p-value < 0.05 was considered statistically significant. All statistical analyses were conducted using IBM SPSS Statistics for Windows, version 29.0 (IBM Corp., Armonk, NY, USA).

3. Results

All participants were healthy, normal-weight Caucasian children aged approximately 5–6 years, who followed either a balanced lacto-ovo-vegetarian or omnivorous diet. The groups were comparable with respect to age (vegetarians: 5.5 ± 0.5 years; omnivores: 5.6 ± 0.6 years) and sex distribution (vegetarians: 47% girls/53% boys; omnivores: 50% girls/50% boys).

3.1. Anthropometric and Body Composition Characteristics

The anthropometric and body composition characteristics of the participants are summarized in Table 1. No statistically significant between-group differences were observed in the basic anthropometric indices, including body weight, height, BMI, or BMI Z-score. Similarly, body composition parameters (fat mass and lean mass) did not differ significantly between the groups. However, omnivorous children showed a non-significant trend toward a higher fat mass percentage compared with vegetarians (21.4% vs. 17.6%, respectively).

Bone mineral outcomes were broadly comparable between the groups. Nevertheless, vegetarian children demonstrated slightly lower values across several bone parameters, including TBLH-BMC (-2.5%), spine BMC (-5.5%), TBLH-BMD (-3.5%), and lumbar spine BMD (L1–L4) (-3.5%). These differences did not reach statistical significance.

3.2. Biochemical Markers of Bone Metabolism and Adipokines

Several significant differences were observed between the groups of vegetarians and omnivores with respect to bone turnover markers and adipokines (Table 2).

Markers of bone formation and carboxylation status of osteocalcin differed between the groups. Vegetarian children had significantly higher BALP activity than omnivores. Total OC concentrations were similar between the groups; however, Glu-OC tended to be lower in vegetarians (p = 0.070), while Gla-OC was significantly higher (p = 0.022). As a result, the Gla-OC/Glu-OC ratio was significantly elevated in vegetarians (p = 0.005).

In parallel, serum CTX-I concentrations were significantly higher in vegetarian children, indicating increased bone resorption. Consequently, the OC/CTX-I ratio, which reflects the balance between bone formation and resorption, was significantly lower in vegetarians. No significant between-group differences were found for serum levels of 25(OH)D, sclerostin, OPG, sRANKL, or the OPG/sRANKL ratio.

Among adipokines, leptin and total adiponectin levels were slightly lower in vegetarians, although these differences were not statistically significant. In contrast, vegetarian children displayed lower HMW adiponectin concentrations (p = 0.050) and the HMW/adiponectin ratio (p = 0.012).

The effect size (ES) was calculated for the seven parameters that differed significantly between the vegetarian and omnivore groups (Fig. 1). Overall, the effects were small, with the largest ES observed for the Gla-OC/Glu-OC ratio (ES = 0.2953) and the HMW/adiponectin ratio (ES = 0.2662).

Figure 1. Mann-Whitney r effect size comparison of the two studied groups of children regarding biochemical parameters.

Figure 1. Mann-Whitney r effect size comparison of the two studied groups of children regarding biochemical parameters.

3.3. Correlation Analyses

The correlation analyses revealed distinct patterns of associations between the anthropometric variables, bone densitometry, bone turnover markers, and adipokines in vegetarian and omnivorous children (Table 3).

In both groups, anthropometric variables, particularly body weight and height, as well as lean mass, were strongly and consistently positively associated with bone outcomes, including total body and spine BMC and BMD. Fat mass also correlated with TBLH-BMC and TBLH-BMD, although these associations were generally weaker than those observed for lean mass.

Notable differences were observed in the relationships between biochemical markers and bone densitometric parameters. In vegetarian children, markers of bone turnover were positively related to bone density measures. Specifically, BALP and CTX-I levels correlated positively with spine BMC (p = 0.027, p = 0.009, respectively). In addition, total OC (p = 0.018), Glu-OC (p = 0.034), and sclerostin (p = 0.027) concentrations were positively associated with lumbar spine BMD (L1–L4). In contrast, among omnivorous children, bone turnover markers were largely unrelated to densitometric indices, with the exception of OPG, which showed consistent negative correlations with BMC and BMD measures (p = 0.020 and p = 0.015, respectively).

Adipokines demonstrated the most pronounced differences between the studied groups. In vegetarians, adipokine concentrations were not significantly associated with bone parameters. Conversely, in omnivorous children, leptin showed strong positive associations (p < 0.001) with multiple bone mineral measures, including both total body and spine outcomes. Total adiponectin was strongly positively correlated with lumbar spine BMD (L1–L4) (p < 0.001), while HMW adiponectin was positively associated with TBLH-BMD (p = 0.025) and lumbar spine BMD (L1–L4) (p = 0.023).

Analyses of the ratio parameters provided additional insights into metabolic interactions (Fig. 2).

Figure 2. Partial Spearman correlation of bone metabolism marker and adipokine ratios with anthropometric and biochemical parameters in children following vegetarian and omnivorous diets.

Figure 2. Partial Spearman correlation of bone metabolism marker and adipokine ratios with anthropometric and biochemical parameters in children following vegetarian and omnivorous diets.

Data from 50 vegetarians and 40 omnivores were analyzed and only statistically significant correlations with p≤0.05 are shown. BMI – body mass index; TBLH – total body less head; BMC – bone mineral content; BMD – bone mineral density; BMD (L1–L4) – lumbar spine (L1–L4) bone mineral density; 25(OH)D – 25-hydroxyvitamin D; OC – osteocalcin; Gla-OC – carboxylated osteocalcin; Glu-OC – undercarboxylated osteocalcin; CTX-I – C-terminal telopeptide of collagen type I; OPG – osteoprotegerin; sRANKL – soluble receptor activator of nuclear factor kappa-B ligand; HMW adiponectin – high molecular weight adiponectin.

In vegetarians, the OC/CTX-I ratio reflected bone formation to bone resorption processes, showed strong expected correlations with OC and CTX-I, but also a weak negative correlation with HMW adiponectin (r = -0.289, p = 0.042). The Gla-OC/Glu-OC ratio demonstrated expected correlations with OC fractions and was negatively correlated with fat mass (r = −0.329, p = 0.019). Adipokine ratios further reflected body composition links: the adiponectin/leptin ratio was negatively correlated with BMI (r = −0.280, p = 0.049) and fat mass (r = −0.374, p = 0.007). The HMW/adiponectin ratio correlated positively with OPG (r = 0.445, p = 0.001) and negatively with sclerostin (r = −0.348, p = 0.013) concentrations.

In omnivores, the ratio parameters showed broader and more integrated correlation patterns. The OC/CTX-I ratio correlated positively with BMI (r = 0.312, p = 0.050), TBLH-BMC (r = 0.353, p = 0.026), and 25(OH)D status (r = 0.372, p = 0.018). The Gla-OC/Glu-OC ratio was positively correlated with TBLH-BMD (r = 0.317, p = 0.047) and negatively with sclerostin concentration (r = -0.371, p = 0.019). The adiponectin/leptin ratio exhibited strong negative correlations with weight (r = -0.426, p = 0.006), BMI (r = -0.635, p < 0.001), fat mass (r = -0.311, p = 0.050), lean mass (r = -0.460, p = 0.003), TBLH-BMC (r = -0.548, p < 0.001), BMC spine (r = -0.512, p = 0.001), TBLH-BMD (r = -0.429, p = 0.006), and BMD (L1–L4) (r = -0.510, p = 0.001). This ratio was also negatively associated with OPG concentration (r = -0.323, p = 0.042). Finally, the HMW/adiponectin ratio was negatively associated with heigh (r = -0.400, p = 0.011) and BMD (L1–L4) (r = -0.417, p = 0.008).

4. Discussion

The present study provides a comprehensive evaluation of bone mineral status, biochemical markers of bone turnover, and adipokine profiles in healthy children aged 5–6-years adhering to lacto-ovo-vegetarian and omnivorous diets. The main findings indicate that despite comparable anthropometric characteristics and bone mineral density between the groups, vegetarian children exhibited subtle but biologically relevant differences in bone remodeling markers and adipokine profiles. This suggests that dietary patterns may influence regulatory mechanisms of bone metabolism during early childhood, even when bone mass remains within the normal physiological range.

Consistent with previous pediatric research, body size and composition were the primary determinants of skeletal development [30,31]. Lean mass showed the strongest positive association with both bone mineral content and bone mineral density, confirming the central role of muscle-derived mechanical loading in bone modeling during growth. In line with earlier studies, vegetarian children (aged 5–10 years) have comparable or slightly lower spine BMC and BMD values, without clinically significant bone deficits [32,33]. The studies by Meyer and Protudjer [34] and Reis et al. [35] support the notion that a well-planned vegetarian diet, adequately supplemented, particularly with vitamin B₁₂, and supervised by qualified healthcare professionals does not impair bone health during childhood. Nevertheless, the degree of dietary restriction and the child’s age remain critical determinants of nutritional risk [22,36].

An important observation in our study was the difference in the relationships between body composition and bone outcomes between the dietary groups. In vegetarian children, bone parameters were primarily associated with lean mass and body weight, while fat mass showed weaker or inconsistent relationships. This pattern suggests that bone development in this group may be driven predominantly by mechanical factors rather than adipose tissue-derived signals. In contrast, omnivorous children exhibited a more integrated pattern, with both lean and fat mass contributing to bone parameters, indicating a broader and more complex metabolic influence on skeletal regulation.

Despite similar bone mineral status, vegetarian children in our study exhibited higher levels of bone turnover markers, including BALP and CTX-I, along with a lower OC/CTX-I ratio. This pattern suggests an imbalance in bone remodeling, with a relative shift toward resorption. Such alterations, although not reflected in current bone mass, may have implications for long-term skeletal health if sustained, potentially affecting peak bone mass and increasing the risk of osteopenia. Similar findings have been reported in pediatric populations consuming plant-based diets, where elevated bone resorption markers and higher PTH concentrations suggest subtle alterations in bone metabolism that may emerge early in life [19,37]. The authors reported a progressive increase in PTH concentrations across dietary groups (omnivorous < vegetarian < vegan), suggesting a shift toward increased bone resorption in more restrictive plant-based diets. Importantly, these findings were not explained by differences in vitamin D status or calcium intake, which were adequate due to supplementation.

A recent study conducted by Itkonen et al. [19] included 2–7-year-old Finnish children and their caregivers on plant-based diets. Among children, no statistically significant differences were observed in primary bone turnover markers: tartrate-resistant acid phosphatase 5b (TRAP5b) and BALP, suggesting similar overall bone remodeling activity across dietary groups. Notably, these alterations appear to become more pronounced with age, as demonstrated in adult populations from similar cohorts. Vegetarian adults had elevated levels either bone formation and bone resorption markers (BALP and TRAP5b), indicating an increase in bone turnover. Together with our findings (higher BALP and CTX-I levels), this suggests that subtle alterations in bone metabolism may already be present in early childhood and become more pronounced later in life. At the same time, vegetarian children in our study also exhibited higher Gla-OC levels and a higher Gla-OC/Glu-OC ratio. This suggests improved vitamin K status, which is essential for the γ-carboxylation of osteocalcin, enabling its binding to hydroxyapatite and supporting bone mineralization. This may reflect higher intake of vitamin K from plant foods and indicates a potentially beneficial effect on bone mineralization, partially offsetting other dietary limitations [38]. This may suggest that certain aspects of vegetarian diets may exert beneficial effects on bone metabolism, potentially offsetting other nutritional limitations.

A novel aspect of this study is the analysis of adipokines in relation to bone parameters. Adipokines, such as leptin and adiponectin are increasingly recognized as important mediators of the crosstalk between energy metabolism and skeletal homeostasis [7,8]. Experimental and clinical studies indicate that leptin can influence bone metabolism both centrally through hypothalamic pathways and peripherally through direct effects on osteoblasts and osteoclasts [39,40]. This is consistent with studies conducted in pediatric populations, including prepubertal children and adolescents, where leptin has been shown to correlate positively with bone mass, particularly in individuals with normal or higher adiposity [41,42,43,44]. Although leptin concentrations did not differ significantly between our studied groups, its association with bone parameters varied. In omnivorous children, leptin was positively associated with BMD, particularly at the lumbar spine and total body, consistent with its proposed anabolic role. In contrast, no such associations were observed in our group of vegetarian children, suggesting that the role of leptin in bone metabolism may depend on body composition and the metabolic context. These findings suggest that the role of leptin in bone metabolism may be context-dependent, influenced by body composition, energy availability, and possibly dietary composition.

Differences were also observed in adiponectin profiles, with vegetarian children exhibiting lower levels of HMW adiponectin, which is the most biologically active isoform. Although the role of adiponectin in bone metabolism remains complex and not fully understood, several studies have reported inverse associations between adiponectin levels and BMD and its influence on bone remodeling [13,39,45,46]. The lower HMW adiponectin level and HMW/adiponectin ratio observed in our group of vegetarian children may indicate subtle differences in adipose-bone signaling, however, the clinical significance of this finding remains unclear and warrants further investigation.

Our analysis of ratio-based biomarkers provides additional insights into the integrated regulation of both bone and metabolic pathways. In vegetarian children, these ratios showed more selective associations, mainly with bone turnover markers, supporting a more compartmentalized regulatory pattern. Additionally, the associations between the HMW/total adiponectin ratio and regulatory markers such as OPG and sclerostin may indicate a potentially protective but indirect role of adipokine isoforms in bone regulation in children on a vegetarian diet. In contrast, omnivorous children exhibited broader associations, linking these ratios not only with bone turnover but also with anthropometric parameters and vitamin D status. The adiponectin-related ratios were consistently negatively associated with both anthropometric and bone parameters. This suggests a more integrated interaction between the skeletal and metabolic pathways in children consuming mixed diets.

Overall, our findings highlight the differences in the regulation of bone metabolism rather than bone mass status in 5–6-year-old vegetarian and omnivorous children. A more mechanically driven and selectively regulated pattern of bone development, accompanied by increased remodeling activity was observed in children on a vegetarian diet. In contrast, a more integrated metabolic profile involving adipokines, bone turnover markers, and body composition was observed in children following a traditional diet.

The main strength of this study is the simultaneous comprehensive assessment of DXA-derived bone parameters, body composition, biochemical bone metabolism markers, and adipokines in a well-characterized cohort of 5–6-year-old children. This integrative approach allowed for the evaluation of both structural and metabolic aspects of bone health and provided insights into bone–adipose tissue interactions. The inclusion of children adhering to a lacto-ovo-vegetarian diet from early life represents a unique and valuable study, provided for the first time. Additionally, the study groups were well matched for age, sex, and anthropometric parameters, minimizing potential confounding factors.

However, several limitations should be acknowledged. The cross-sectional design limits causal interpretation. The relatively small sample size and single-center setting may have reduce the statistical power to detect subtle differences in bone mineral parameters. In addition, although the children followed balanced diets, detailed dietary intake data, particularly for protein, and specific micronutrients including calcium, and vitamin K, were not available. This limited the direct assessment of nutrient–biomarker relationships. Future longitudinal studies incorporating detailed nutritional assessment are needed to better understand the long-term implications of these findings.

5. Conclusions

In conclusion, children aged 5–6 years following vegetarian or omnivorous diets exhibit comparable growth, body composition, and bone mineral density, indicating that well-planned vegetarian diets do not impair early skeletal development. However, differences in bone turnover markers and adipokine–bone interactions suggest distinct regulatory patterns of bone metabolism. Vegetarian children demonstrate an imbalance in bone turnover and a more selective, mechanically driven pattern of skeletal regulation, whereas omnivorous children display a more metabolically integrated profile involving adiposity-related signals. These findings highlight the importance of combining densitometric, bone metabolism markers and adipokine assessments when evaluating bone health in children and underscore the need for careful nutritional planning in plant-based diets during early life.