Doctors have long noted that baby boys tend to be born heavier than baby girls. Researchers from the Harvard School of Public Health and the Karolinska Institutet in Stockholm, Sweden, may have uncovered the reason. Their recent study of 244 American women shows that women pregnant with a male embryo actually eat 10 percent more calories on average than those carrying a girl. Notably, the increased food intake had no impact on the mothers' weight - all the extra nutrients seem to go directly to the fetus.