Breast-fed infants given solid foods at 4 months of age grow no faster than do those who first receive solid foods at 6 months, and there may be disadvantages to earlier introduction of complementary foods, according to a study in Latin America by nutritionists at the University of California, Davis. Their findings will appear in the July 30 issue of the British medical journal Lancet. "Early introduction of solid foods to any breast-fed baby will likely decrease its intake of nutrient-rich breast milk, but is particularly risky in developing nations, where the lack of proper sanitation may increase the chance of food contamination," said study co-author Kathryn G. Dewey, a UC Davis professor of nutrition and an authority on maternal and child nutrition. In a study, completed by 141 women and their babies in the low-income Honduran city of San Pedro Sula, graduate student Roberta Cohen, Dewey and colleagues found that early introduction of solid foods at the age of 4 months, rather than 6 months, provided no advantages in terms of increased caloric intake or infant growth. Furthermore, babies receiving solid foods significantly decreased their breast milk intake. While breast-feeding is recommended worldwide as the best method for feeding young infants, there has been considerable debate over when to introduce solid foods. In light of the World Health Organization's recommendation to offer complementary foods to breast-fed babies sometime between 4 and 6 months of age, the UC Davis nutritionists set out to determine if there was any advantage to starting infants on solid foods at the earlier end of that age span. "We were particularly interested in determining whether complementary foods introduced before 6 months actually increased the infant's total energy intake or merely displaced breast milk," said Cohen. The nutritionists monitored breast milk intake, total energy intake and growth of the infants from the age of 16 weeks to 26 weeks. The mothers and their babies were randomly assigned to either a control group, whose participants exclusively breast-fed their infants; a group that introduced solid foods at 16 weeks, while breast-feeding only according to infant demand; or a group that introduced solid foods at 16 weeks, but maintained the same schedule of breast-feeding as they had before the study. Commercial baby food was used to avoid any increase in illness or nutrient deficiency that might result from home-prepared foods. The food included rice cereal, egg yolk, fruits and vegetables, all of which were locally used as weaning foods. While the exclusively breast-fed babies maintained their breast milk intake during the study, researchers found that the infants receiving solid foods reduced the frequency and duration of nursing, dramatically decreasing their intake of breast milk. This apparent replacement of breast milk by solid foods supports indications from earlier research that breast-fed infants have a "self-regulating" mechanism whereby they maintain a given energy intake level, said Dewey. There were no significant differences between the three groups in infant growth, measured in terms of weight and length. Likewise, common infant ailments, such as upper respiratory illnesses and diarrhea, were quite low in all three study groups. "In developing countries there is normally a marked increase in illnesses accompanying the introduction of solid foods," Cohen said. "Had we not provided pre-prepared baby foods in this study, the rate of illness probably would have been higher for those infants receiving solid foods." Furthermore, researchers found that the infants in the study, 20 percent of whom were born with low birth weights (less than 5.5 pounds), grew more rapidly than do breast-fed infants in the United States up to the age of 4 months and at a rate very similar to their U.S. counterparts from 4 months to 6 months of age. "It has been suggested that breast-fed infants in developing countries falter in their growth rate by the age of 6 months, perhaps due to maternal malnutrition," said Dewey. "In the Honduran study, however, lactation performance was not compromised nor was there growth faltering, even though the mothers in the study were low-income and many had marginal diets." The satisfactory infant growth in the Honduran study may be due to the constant encouragement mothers received from the research team to continue exclusively breast-feeding their babies, Cohen said. Collaborating with Cohen and Dewey on the study were Kenneth A. Brown, a UC Davis professor of nutrition; Judy Canahuati, former director of the La Leche League in San Pedro Sula, Honduras; and Leonardo Landa Rivera, a medical adviser to La Leche League in San Pedro Sula, Honduras. The study was supported by the Thrasher Research Fund, the World Health Organization, the Institute for Reproductive Health, Georgetown University and UNICEF/Honduras.