One of the most common questions I get has to do with the color of a newborn’s bowel movements. The first stool that an infant has is a dark green, black substance called meconium. Babies pass meconium stools for a few days before they have something called transitional stools. Transitional stools are usually a medium green color and runny. In many cases, transitional stools can “shoot” out of a baby’s bottom like diarrhea.

Breastfed babies usually have loose, seedy or runny stools. They can be yellow, green or brownish in color. The reason parents worry about green stools in babies is because older children and adults only have green bowel movements when they are sick. There is a simple explanation for this.

The body uses bile acids to digest fats. Bile is pea green in color. In children and adults, waste moves through the large intestine slower than in newborns. This allows the “good” bacteria that live in the intestine to metabolize the bile, which converts it to a brownish color. Because fecal material moves through a newborn’s intestinal tract rapidly, there is less time for intestinal bacteria to convert the bile from green to brown. When children and adults have diarrhea, peristalsis is sped up causing green poops.