Leptin in Breast-Fed and Formula-Fed Infants

Abstract

Introduction: Leptin is a hormone present in breast milk, but not in formula, which regulates food intake and energy metabolism; it could be one of the factors involved in preventing obesity. Breast milk leptin provides a physiologic explanation for some of the advantages seen in normal growth, regulation of energy intake and immunological status in breast-fed (BF) compared with formula-fed (FF) infants. Aim: To see whether leptin levels are different in BF or FF infants in the first months of life. Methods: We studied 186 AGA healthy infants, in the first 22 m, without any disease of the gastrointestinal tract, admitted to our Department during the period between June 2000 and August 2003. Serum leptin concentration was determined at least 3 h post-feeding by RIA test (LEP-R44 Mediagnostic, Reutlingen, Germany). For each infant the parents filled up a form for the Ethical Committee. Statistical Analysis: Student t-test was performed. Statistical significance was set at p<0.05. Data have been normalized with natural logarithm. Results: A significant difference (p=0.044) appeared in the first 4 m (n=82) between breast-fed (BF) (1.16 ± 0.99 ng/ml) and formula-fed (FF) (0.68 ± 1.11 ng/ml) infants. Between 4 and 8 m of age there were no differences in leptin levels between feeding groups (BF (n=21): 0.73 ± 1.03 ng/ml; FF (n=15): 0.55 ± 0.84 ng/ml). Similar results have been found in infants between 8 and 12 m (n=32; BF: 0.27 ± 1.01 ng/ml; FF: 0.71 ± 0.87 ng/ml). Conclusions: Published data show that leptin levels are higher in breast-fed infants than in formula-fed ones. Breast-fed infants feed more frequently and take in less per feed compared with formula-fed infants. The presence of leptin in breast milk may have a positive effect on satiety and regulation of energy intake. The long-term consequences of this difference between BF and FF infants and the role of leptin in promoting later obesity are unknown.