Researchers have shown that an infant's first food affects his or her gene expression, giving a possible mechanism for how breast milk impacts health. (Gene expression is the process by which instructions in a gene are used to synthesize a functional gene product, mostly proteins. When genes are expressed, it is as if they are "turned on.")
"Genes are really sensitive to nutrition," said study researcher Sharon Donovan of the University of Illinois. "And we now have genes that may explain many of the clinical observations of how breast-fed and formula-fed  differ."
Using a novel noninvasive technique, researchers compared 10 formula-fed 3-month-olds with 12 breast-fed infants of the same age. Capitalizing on the natural sloughing off of intestinal cells during digestion, the researchers looked for signs of gene expression, in the form of messenger RNA, in the babies' poop.
Breast milk and formula have different effects on at least 146 genes, the researchers found.
Most of the genes enhanced by breast milk promote quick development of the intestine and immune system, Donovan told LiveScience.