[Effects of the timing of complementary food on infant physical development].

Objective: To analyze the timing of supplementary food and its effect on the development of infants at 6-8 months of age.

Methods: A total of 168 breastfed healthy infants in Beijing and Chenzhou were selected and followed up from birth to 8 months of age. According to the time of the first supplementary food addition, the survey subjects were divided into a reasonable supplementary food group and an unreasonable supplementary food group. Repeated measures analysis was used to compare the differences in the Z scores of the two groups of infants.

Results: Infants who added complementary food between 4-6 months accounted for 80.4%(n=135). There were 6.0%(n=10) of infants who added complementary food for more than 8 months of age(added too late), and the timing was earlier than 4 months old infants accounted for 6.5%(n=11). The result of repeated measurement analysis showed that the body mass index for age Z score(BAZ) of infants whose complementary foods were added at an unreasonable time was different from that of infants with reasonable complementary food addition(P=0.046). Infants whose complementary food was added at an unreasonable time had higher BAZ at the age of 6 months(β=0.615, 95%CI 0.053-1.178).

Conclusion: Few infants add complementary foods too early or too late, and the timing of complementary foods for most infants was between 4-6 months of age. Unreasonable complementary food addition time might have a short-term impact on the infants' BAZ.