In a study published in the Canadian Medical Association Journal, researchers led by Anita Kozyrskyj found that babies born by C-section harbored a different set of microbes in their digestive tracts than those born vaginally, and that infants who were breast-fed had a different recipe of bacteria in their guts than those who were given formula.
Researchers looked at the nutritional value of including two different varieties of egg yolks as weaning foods for a group of breast-fed and formula-fed infants.