Complementary feeding with cow's milk alters sleeping metabolic rate in breast-fed infants

Although it is widely accepted that energy expenditure in infants is a function of feeding pattern, the mechanism behind this is not well understood. The objectives of this observational study were as follows: 1) to compare minimal observable energy expenditure (MOEE) between 2 subgroups of breast-fed infants, a BM group in which breast milk was the only source of milk and a BCM group given cow's milk in addition to breast milk; and 2) to identify potential mediators of a feeding pattern effect. For this purpose, infants were classified by feeding group on the basis of a mother's recall. Respiration calorimetry was used to measure MOEE in 62 infants (n = 35 BM, n = 27 BCM) aged 8.7 mo in Pelotas, southern Brazil. Breast-milk intake was measured using deuterium oxide, complementary food intake by 1-d food weighing, total energy expenditure and total body water using doubly labeled water; anthropometric indices were calculated. MOEE was 1672 [+ or -] 175 kJ/d in BM compared with 1858 [+ or -] 210 kJ/d in BCM infants (P < 0.001). Mass-specific MOEE was 201 [+ or -] 24.6 and 216 [+ or -] 31.9 kJ/(kg * d) in BM and BCM infants, respectively (P = 0.041). MOEE (kJ/d) was mediated by protein intake and fat-free mass ([R.sup.2] = 41.4%). We conclude that complementary feeding with cow's milk alters the sleeping metabolic rate in breast-fed infants. These findings deserve attention in relation to 'metabolic programming' and the development of obesity later in life. J. Nutr. 135: 1889-1895, 2005. KEY WORDS: * minimal observable energy expenditure * sleeping metabolic rate * breast milk * cow's milk * infants