A physiological role of breast milk leptin in body weight control in developing infants

Objective: Leptin, a hormone that regulates food intake and energy metabolism, is present in breast milk. The aim of this study was to determine whether milk leptin concentration is correlated with maternal circulating leptin and BMI and with body weight gain of infants. Research Methods and Procedures: A group of 28 non‐obese women (BMI between 16.3 and 27.3 kg/m²) who breast‐fed their infants for at least 6 months and their infants were studied. Venous blood and milk samples were obtained from mothers at 1, 3, 6, and 9 months of lactation, and leptin concentration was determined. Infant body weight and height were followed until 2 years of age. Results: During the whole lactation period, milk leptin concentration correlated positively with maternal plasma leptin concentration and with maternal BMI. In addition, milk leptin concentration at 1 month of lactation was negatively correlated with infant BMI at 18 and 24 months of age. A better negative correlation was also found between log milk leptin concentration at 1 and at 3 months of lactation and infant BMI from 12 to 24 months of age. Discussion: We concluded that, in a group of non‐obese mothers, infant body weight during the first 2 years may be influenced by milk leptin concentration during the first stages of lactation. Thus, moderate milk‐borne maternal leptin appears to provide moderate protection to infants from an excess of weight gain. These results seem to point out that milk leptin is an important factor that could explain, at least partially, the major risk of obesity of formula‐fed infants with respect to breast‐fed infants.