Evaluation of leptin and IGF-1 levels in breast milk and their effects on eating behavior in infants with different growth rates

Objective. To evaluate the levels of insulin-like growth factor 1 (IGF-1) and leptin in breast milk (BM) of mothers of infants with different growth rates during lactation in relation to infants’ daily biorhythms and eating behavior and maternal genetic predisposition to obesity. Patients and methods. The study included 103 mothers aged 32.2 ± 0.5 years (M ± m) with a body mass index (BMI) of 19.8 ± 2.8 kg/m2 and their children who were exclusively breastfed for 3 months. Body weight and length were measured in all infants at birth and at 1 and 3 months of age, after which compliance with the standard population (WHO Anthro) was assessed. According to the rate of change in BMI Z-score from birth to 3 months of age, infants were divided into 2 groups: group 1 – low rate (delta BMI Z-score < 0.67, n = 45); group 2 – high rate (delta BMI Z-score ≥ 0.67, n = 58). BM samples were collected on day 10–14, at 1 and 3 months of lactation by decanting the middle portion of milk during the morning feeding. The levels of IGF-1 and leptin in BM were determined by ELISA. The identification of rs9939609 polymorphism in the FTO gene by real-time PCR was performed in all women. Eating behavior of infants was assessed using the BEBQ questionnaire, and daily biorhythms were assessed by mothers completing diaries of infant crying and restless behavior. Results. The median growth rate in infants during the first 3 months of age was 0.11 [-0.25;0.38] in group 1 and 1.29 [0.87;1.24] in group 2, p = 0.000. At birth, infants in group 1 showed significantly higher Z-scores associated with body weight. A significantly higher number of carriers of obesity-related risk allele A and higher height were found among mothers in group 1 compared to mothers in group 2. At 3 months of age, group 1 had significantly higher length-for-age Z-score (p = 0.04) and low BMI and weight-for-length Z-scores (p = 0.003) compared to group 2. Group 1 compared to group 2 showed higher levels of IGF-1 (p10–14 days = 0.023) and lower levels of leptin (p10–14 days = 0.001; p1 month = 0.002) in BM. Differences in BM hormone levels were accompanied by differences in daily biorhythms and eating behavior. Infants in group 2 were less likely to breastfeed and spent more time awake, fed for more than 30 minutes, and finished eating quickly. Conclusion. Infants with a high rate of change in BMI Z-score consumed BM with high levels of leptin, which has anorexigenic activity, and with low levels of IGF-1, which does not stimulate growth activity and appetite. This leads to a significant decrease in length-for-age Z-score at 3 months of age and a significant increase in BMI and weight-for-length Z-scores. The reasons for differences in the hormonal composition of BM may be both genetic and other factors that require further research. Key words: breast milk, exclusive breastfeeding, IGF-1, leptin, eating behavior, growth rate, daily biorhythms, rs9939609