Introduction
Food allergy (FA) is one of the most common childhood disorders, with increasing prevalence worldwide (1). In infancy, FA may present with eczema, gastrointestinal symptoms, feeding difficulties, and dietary restrictions, all of which may adversely affect nutritional status and growth (2). Although multiple studies have suggested an association between FA and impaired growth outcomes, particularly in children with severe or multi-food allergies-the overall evidence remains inconsistent, and the underlying mechanisms have not been fully elucidated (3, 4).
Breastfeeding is universally recommended as the optimal source of nutrition during early life, including for infants with diagnosed or suspected FA (5). In clinical practice, mothers of infants with suspected or confirmed FA frequently adopt elimination diets, either on medical advice or based on personal concerns (6). While targeted elimination of specific allergens may be clinically justified in selected cases, excessive or prolonged dietary restriction can compromise maternal nutrient intake and dietary diversity, potentially altering the nutritional composition of breast milk and indirectly influencing infant growth (7, 8).
Importantly, current international guidelines do not support routine maternal dietary avoidance for allergy prevention and instead caution against unnecessary restriction during breastfeeding (9).
Despite these considerations, most previous research on growth in children with FA has focused primarily on dietary restriction applied directly to affected children, as well as on feeding difficulties and nutrient deficiencies in pediatric populations (10, 11). By contrast, relatively few studies have described maternal dietary behavior during lactation in relation to growth among exclusively breastfed infants with FA. Moreover, existing evidence is largely derived from cross-sectional analyses or mixed feeding populations, limiting the ability to characterize dynamic growth trajectories during exclusive breastfeeding (12, 13).
Consequently, longitudinal growth patterns in exclusively breastfed infants with FA, together with the maternal dietary practices accompanying this condition, remain insufficiently characterized.
To address this gap, we conducted a prospective longitudinal cohort study of exclusively breastfed infants with and without FA. By focusing on a homogeneous feeding pattern during early infancy and using repeated anthropometric assessments, we aimed to characterize longitudinal growth trajectories in infants with and without FA and to describe maternal dietary avoidance practices during exclusive breastfeeding.
Materials and methods
Study design and participants
This was a longitudinal cohort study conducted at the Child Health Care Department of the Children’s Hospital of Chongqing Medical University, Chongqing, China. A total of 73 mother-infant pairs were enrolled between November 2024 and November 2025. This cohort focused specifically on exclusively breastfed infants with clinically diagnosed FA, a population in which longitudinal growth data remain limited.
The repeated-measures design, with up to five observations per infant, provides enhanced statistical efficiency for detecting growth trajectory differences between groups. Infants were eligible if they were: (1) 4–6 months of age at enrollment; (2) exclusively breastfed; (3) full-term (gestational age ≥ 37 weeks and < 42 weeks); and (4) free of major congenital diseases. Exclusion criteria included neonatal hospitalization > 30 days, major illness or surgery during follow-up, or relocation that precluded continued follow-up.
Infants with any diagnosed comorbidity that could affect growth (e.g., congenital heart disease, chronic lung disease, endocrine disorders, chromosomal abnormalities, or significant gastroesophageal reflux disease requiring medical treatment) were also excluded.
Diagnosis of food allergy (clinical assessment)
In this pragmatic real-world cohort, FA was diagnosed clinically based on symptom response to maternal dietary elimination and subsequent reintroduction, rather than by universal oral food challenges (OFC). This approach reflects standard clinical practice for breastfed infants—where OFC is often infeasible—and aligns with previous observational studies (14, 15).
All infants were evaluated by experienced pediatric allergists using a standardized algorithm, comprising five sequential steps: first, a detailed clinical history was obtained, assessing presenting symptoms (skin: eczema, urticaria, angioedema; gastrointestinal: vomiting, diarrhea, blood in stool, poor feeding; respiratory: wheeze, rhinitis), timing of symptom onset in relation to feeding, and family history of atopy; second, a systematic physical examination was performed to evaluate cutaneous manifestations, growth parameters, and systemic signs of allergic disease; third, for suspected cases, mothers eliminated the suspected allergen(s) from their diet for 2–4 weeks, with the specific foods eliminated based on clinical history and symptom pattern; fourth, clinical improvement following maternal elimination was recorded; and fifth, suspected foods were reintroduced one at a time over 3–5 days, with careful monitoring for symptom recurrence, where a positive response was defined as reproducible symptom recurrence within 24–72 h of reintroduction. Infants were assigned to the non-FA group if they had no history of reproducible allergic symptoms, no clinical signs of allergic disease on examination, and no evidence of allergic sensitization according to the assessing allergist. We emphasize that FA diagnoses in this cohort are clinically based and should not be equated with universally challenge-confirmed FA; throughout this manuscript, “FA” refers to this clinically defined entity.
Data collection and follow-up
Infants were enrolled at 4–6 months of age (before complementary feeding introduction) and followed prospectively according to routine well-child visit schedules: monthly at 4, 5, 6 months of age, and then every 2 months at 8, 10, and 12 months of age. The follow-up interval from 6 to 8 months represents a 2-month gap, as visits occurred at 6 months and then again at 8 months. At each visit, weight and length were measured by trained nurses using standardized equipment.
Anthropometric measurements were converted to age- and sex-specific Z-scores, including weight-for-age Z-score (WAZ), length-for-age Z-score (LAZ), weight-for-length Z-score (WLZ), and head circumference-for-age Z-score (HCZ), using the WHO Child Growth Standards (R package Anthro) (16). At enrollment, maternal dietary avoidance practices since the infant‘s birth were documented using a structured questionnaire that captured: avoided food categories (milk, eggs, wheat, soy, nuts, fish, shellfish, peanuts), duration of avoidance and reasons for avoidance.
Ethics statement
This study was approved by the Ethics Committee of the Children’s Hospital of Chongqing Medical University (Approval No.: 2024 Lun Shen (Lin Yan) Pi Jian No. (419); Clinical Research Registration No.: MR-50-25-026075) and was registered in the Chinese Clinical Trial Registry (Registration No.: ChiCTR2500114005). Written informed consent was obtained from the legal guardians of the participants.
Statistical analysis
Longitudinal growth trajectories were analyzed using linear mixed-effects models (LMMs) with random intercepts for each infant to account for within-subject correlations arising from repeated measurements. Separate models were fitted for WLZ, WAZ, and LAZ as outcome variables. Fixed effects included group (FA vs.
NFA), age (centered at 5 months), the group-by-age interaction, and infant sex as a covariate. The group-by-age interaction was used to evaluate whether longitudinal changes in growth differed between the FA and NFA groups.
For descriptive presentation, observed growth Z-scores were summarized by predefined age intervals (4 to <6, 6 to <8, 8 to <10, 10 to <12, and ≥12 months). These age-specific summaries were treated as descriptive, whereas longitudinal statistical inference was based on the mixed-effects models.
To assess the adequacy of the linear age specification, sensitivity analyses were performed by adding quadratic age terms and group-by-quadratic-age interactions to the longitudinal models. In additional sensitivity analyses, group-by-sex interaction terms were examined to assess potential effect modification by infant sex.
Model assumptions were evaluated using residual-versus-fitted plots and quantile–quantile plots of residuals. Model convergence and singularity were also examined. All statistical analyses were performed using R version 4.3.3.
All tests were two-sided, and p < 0.05 was considered statistically significant.
Results
Participant characteristics
A total of 73 mother–infant pairs (30 in the FA group and 43 in the NFA group) were included, contributing 268 anthropometric observations to the longitudinal analysis (mean, 3.67 observations per infant). The number of available observations varied across age intervals and decreased at later follow-up. Group-specific sample sizes for each predefined age interval are presented in Table 1.
The most common FA phenotypes in the FA group were cow’s milk protein allergy (n = 18, 60.0%), egg allergy (n = 13, 43.3%), shellfish allergy (n = 12, 40.0%), fish allergy (n = 8, 26.7%), and peanut allergy (n = 5, 16.7%). The distribution of FA phenotypes is shown in Supplementary Table S1. Maternal dietary avoidance was substantially more prevalent in the FA group than in the NFA group (83.3% vs.
18.6%, p < 0.001), with a significantly greater number of avoided foods (median 3 vs. 1, p = 0.003). The most avoided foods in the FA group were milk (53.3%), fish (53.3%), shellfish (50.0%), eggs (40.0%), wheat (23.3%), soy (16.7%), and peanuts (10.0%).
Reasons for maternal dietary avoidance differed substantially between groups. In the FA group (n = 25, 83.3%), all cases of dietary avoidance were initiated due to suspected or confirmed infant FA. Of these, 20 (80%) were physician-recommended, and 5 (20%) were initiated by mothers based on personal concerns (with subsequent physician confirmation).
In the NFA group (n = 8, 18.6%), avoidance was primarily driven by maternal personal factors: maternal allergy/intolerance (n = 2, 25%), and concern about infant colic (n = 6, 75%). None of the NFA group mothers reported avoidance due to physician recommendation for infant FA. Most baseline characteristics were similar between groups, with the exception of maternal dietary avoidance practices.
Breastfeeding duration was comparable between groups (Table 2). Detailed feeding frequency and duration per feed were not systematically recorded in this study. No infants in either group had major comorbidities that could independently affect growth, as per the exclusion criteria.
Maternal dietary avoidance patterns
Maternal dietary avoidance was markedly more common among mothers of infants with FA than among those without FA. The crude odds ratio for dietary avoidance in the FA group was 16.50(95% CI 5.01–54.38). This association remained highly significant after adjustment for maternal age (continuous), maternal education level (categorical: bachelor or above vs. below bachelor), and family history of allergy (binary) (adjusted OR 14.14, 95% CI 4.04–49.57, p < 0.001), indicating that maternal avoidance practices were strongly associated with the presence of infant FA.
Mothers of infants with FA avoided a significantly greater number of food categories than mothers in the NFA group (median 3 vs. 1, p = 0.003).
Descriptive growth measures across age intervals
Observed growth Z-scores according to the predefined age intervals are summarized in Table 1. The descriptive values showed that mean WLZ was lower in the FA group than in the NFA group during the earlier age intervals, whereas group differences were smaller at later ages. However, these age-specific summaries were not used for inferential testing, and longitudinal group differences were evaluated using the mixed-effects models described below.
The number of available observations decreased at later follow-up, particularly in the FA group, and estimates at later ages should therefore be interpreted cautiously.
Longitudinal growth trajectories
Linear mixed-effects models were used to evaluate longitudinal growth trajectories using all available repeated anthropometric measurements (Table 3).
For WLZ, the estimated difference between the NFA and FA groups at the centered age of 5 months was 0.423 Z-score units (95% CI 0.036 to 0.811, p = 0.035), with lower estimated WLZ in the FA group. The age effect was −0.054 Z-score units per month (95% CI − 0.119 to 0.011, p = 0.105). There was no evidence of a group-by-age interaction (estimate = −0.011, 95% CI − 0.086 to 0.063, p = 0.763), indicating that the linear rate of WLZ change did not differ significantly between groups.
For WAZ and LAZ, significant linear group-by-age interactions were observed (WAZ: estimate = 0.156, 95% CI 0.065 to 0.247, p < 0.001; LAZ: estimate = 0.202, 95% CI 0.109 to 0.296, p < 0.001). However, quadratic sensitivity analyses indicated significant nonlinear age patterns for both outcomes; therefore, these linear interaction estimates were interpreted cautiously rather than as evidence of constant linear divergence over time.
Sensitivity analysis did not support a nonlinear WLZ trajectory: adding quadratic age terms did not significantly improve model fit (p = 0.192), and the group-by-quadratic-age interaction was not significant (p = 0.656). Additional sensitivity analyses showed no evidence of group-by-sex interactions for WLZ (p = 0.599), WAZ (p = 0.980), or LAZ (p = 0.825).
Model-predicted WLZ trajectories with 95% confidence intervals and observed age-specific group means are shown in Figure 1. Quadratic WAZ and LAZ trajectories are provided in Supplementary Figure S1.
Discussion
In this prospective longitudinal cohort of exclusively breastfed infants, infants with clinically diagnosed FA had lower estimated WLZ around 5 months of age than infants without FA. This finding is broadly consistent with previous studies reporting increased vulnerability to growth impairment among children with FA, particularly those with gastrointestinal manifestations, feeding difficulties, or extensive dietary restrictions (14, 17, 18). Maternal dietary avoidance was also substantially more common among mothers of infants with FA, consistent with the frequent use of dietary modification in the clinical management of suspected or confirmed infant FA (19–21).
However, in the present longitudinal analysis, there was no evidence that the linear rate of WLZ change differed between groups over time. A WLZ of zero represents the median of the WHO reference population rather than the expected mean of every study sample; therefore, positive mean WLZ values in this cohort do not themselves indicate abnormal growth (22).
By restricting the cohort to exclusively breastfed infants and using repeated anthropometric assessments, our study provides a focused view of early growth patterns and accompanying maternal dietary practices.
Maternal dietary avoidance may have nutritional implications through several pathways. Extensive avoidance of milk, eggs, wheat, fish, or other major food groups may reduce maternal dietary diversity and nutritional adequacy, particularly when such restriction occurs without professional nutritional counseling (23, 24). Maternal dietary avoidance may also reflect the clinical burden of infant symptoms, because mothers of more symptomatic infants may be more likely to adopt restrictive diets (18).
In the present cohort, maternal dietary avoidance was substantially more frequent among mothers of infants with FA; however, because the revised analysis does not establish an independent association between maternal avoidance and infant growth, these mechanisms should be regarded as clinically plausible considerations rather than explanations directly demonstrated by our data. Complementary feeding may nevertheless be relevant to subsequent growth trajectories in infants with FA. As complementary foods are introduced, dietary diversity and nutrient sources increase beyond breast milk alone, which may influence weight gain and body proportionality during later infancy.
However, detailed information on the timing, composition, quantity, and nutrient density of complementary foods was not collected in this cohort. Therefore, the present data cannot determine whether complementary feeding contributed to the later growth pattern observed in either group. Future prospective studies incorporating detailed complementary feeding records will be needed to assess whether dietary diversification modifies growth trajectories in infants with FA.
The longitudinal patterns of WAZ and LAZ differed from that of WLZ. In the primary linear models, significant group-by-age interactions were observed for both WAZ and LAZ. However, quadratic sensitivity analyses indicated significant nonlinear age patterns for these outcomes, suggesting that their trajectories were not adequately summarized by a constant linear slope over time.
These findings should therefore be interpreted cautiously and as evidence of more complex age-related growth patterns rather than simple linear divergence between the FA and NFA groups. By contrast, the WLZ trajectory was adequately described by the linear model, and no significant group-by-age interaction was detected. WLZ is a standardized measure of weight relative to length and is commonly used to assess body proportionality in infancy (22).
Implications and limitations
These findings support close growth monitoring in exclusively breastfed infants with FA. Maternal dietary avoidance was common among mothers of infants with FA, and when dietary restriction is clinically necessary, individualized nutritional counseling may help maintain maternal dietary adequacy and avoid unnecessary restriction.
This study has several strengths, including its prospective longitudinal design, repeated anthropometric measurements, focus on exclusively breastfed infants, and use of mixed-effects models to account for within-infant correlation. Several limitations should also be acknowledged. First, the sample size was modest, particularly at later follow-up ages, which limited the precision of age-specific descriptive estimates and secondary analyses.
Second, detailed information on complementary feeding practices and nutrient intake was unavailable, precluding direct evaluation of their contribution to later growth patterns. Third, maternal dietary avoidance was assessed retrospectively at enrollment and detailed maternal energy, protein, and micronutrient intake were not measured, limiting interpretation of its nutritional implications. Fourth, because oral food challenges were not systematically performed, FA diagnosis was based primarily on clinical assessment and response to elimination and reintroduction, and IgE- and non-IgE-mediated phenotypes could not be distinguished.
Fifth, follow-up attendance varied across age intervals, and the number of available observations decreased at later ages, particularly in the FA group. Mixed-effects models accommodated unequal numbers of repeated observations across infants, although differential follow-up may still have affected the precision of estimates at later ages. Finally, the observational, single-center design limits causal inference and generalizability to other populations and clinical settings.
Larger prospective studies with detailed maternal and complementary feeding assessments are needed to clarify the relationships among FA, maternal dietary practices, and infant growth.
Conclusion
Infants with clinically diagnosed FA had lower estimated WLZ around 5 months of age than infants without FA, but no significant difference in the linear rate of WLZ change was detected between groups over time. Maternal dietary avoidance was markedly more common in the FA group. These findings support close growth monitoring and appropriate nutritional counseling for breastfed infants with FA and their mothers.
Further prospective studies with detailed dietary assessment are needed to clarify the links among FA, maternal dietary practices, and infant growth.