['Previous studies have shown that giving other foods while breastfeeding increases the risk of mother-to-child transmission of human immunodeficiency virus (HIV) type 1. The mechanism is speculated to be increased inflammation of the gastrointestinal tract.', 'In a prospective longitudinal study, we compared fecal calprotectin, a marker of intestinal inflammatory disease, in healthy U.S. infants 0-6 months of age who were exclusively breastfed compared to those given additional liquids or solids.', 'In comparison to infants who were mixed-fed, fecal calprotectin was significantly higher in the exclusively breastfed group (p = 0.01) by a mean of 60 mg/kg (SE = 23).'] Are fecal calprotectin concentrations higher in exclusively breastfed infants compared to those who are mixed-fed?