Objectives: The present study evaluated anthropometry Z-scores of exclusively breastfed infants aged 0~6 months and examined their associations with various parent–infant factors. Methods: This cross-sectional study included 383 mother–infant dyads from 10 Chinese cities in the final analyses, under strict inclusion and exclusion criteria. Data were collected by trained investigators using questionnaires covering demographic characteristics, perinatal health, maternal and infant factors during lactation. Nutrient intake was assessed and calculated by 24 h recall. Anthropometric measurements of parents and infants were taken using calibrated instruments, with infant growth assessed via Chinese growth standards. Statistical analyses included correlation and linear mixed-effect models accounting for regional clustering, with variable selection guided by backward elimination step regression. Nonlinear relationships were explored using spline and piecewise regression methods. Results: Over 60% of the mothers had inadequate energy and protein intake. Approximately two-thirds of the participants had fat intakes exceeding the upper limit. Inadequate or excessive gestational weight gain, poor maternal sleep quality, lactational mastitis, higher maternal fat intake and infant gastrointestinal symptoms were associated with lower infant anthropometry Z-scores. A threshold effect was detected between maternal fat intake and infant WAZ, BMI Z, and WLZ. Conclusions: This study found that anthropometry Z-scores of exclusively breastfed infants aged 0–6 months were significantly associated with certain maternal–infant factors and maternal fat intake, emphasizing the need for early intervention on adverse factors and balanced maternal diet nutrition during lactation.

Background/Objectives: Evidence suggests that partially hydrolyzed whey protein promotes appropriate infant growth; however, research on its long-term effects, especially in Asia, remains limited. This study set out to evaluate the effects of an infant formula containing partially hydrolyzed whey and intact protein on infant growth and development. Methods: This multicenter, triple-blind, randomized non-inferiority trial enrolled healthy full-term infants (≤14 days old). Participants were randomized (1:1) to receive pHF (n = 78) or SF (n = 70) until 6 months of age, with propensity score-matched exclusively breastfed (BF) infants (n = 70) serving as the reference. The primary outcome was daily weight gain. Linear mixed models assessed the association between feeding type and WHO z-scores over time. Results: Over 6 months, the adjusted mean (SE) daily weight gain (g) was 26.4 (1.27) g/day in BF, 26.0 (1.19) g/day in pHF, and 25.3 (1.27) g/day in the SF group. The adjusted mean difference between pHF and SF was 0.64 g/day (95%CI: −1.55, 2.83), confirming non-inferiority. Growth parameters were comparable between pHF and SF, with WHO z-scores remaining within ±1 SD of reference standards. Compared with pHF, SF was associated with a slower increase in length-for-age z score (LAZ). While there was no difference between the pHF and BF groups, WAZ increased significantly less in SF vs. BF [−0.34 (95%CI: −0.58, −0.10), p = 0.003]. Gastrointestinal disorders occurred more frequently in the SF group than in the BF group, with no significant difference between the pHF and BF groups. Conclusions: An infant formula containing partially hydrolyzed whey and intact protein supported adequate growth and was well tolerated during the first six months of life, with growth trajectories comparable to those of breastfed infants.