Effects of feeding infant formula rich in sn-2 palmitate for 6 months on fecal saponified fatty acids, calcium and stool characteristics: a cluster-randomized controlled trial.

BACKGROUND: Human milk palmitic acid (PA) is mainly esterified at the sn-2 position of triacylglycerols, while infant formula contains palmitate predominantly in the sn-1/3 positions. Current evidence on long-term health effects of increasing sn-2 palmitate in formula remains insufficient. This study investigated the effects of high sn-2 PA formula (> 40%) on fecal saponified fatty acid, calcium, magnesium and stool characteristics in healthy full-term infants. METHODS: In this cluster-randomized controlled trial, healthy infants < 14 d were assigned to breastfeeding (BF group, n = 66), high sn-2 palmitate formula (sn-2 group, n = 66, 46.3% sn-2 PA) or low sn-2 palmitate formula (control group, n = 67, 10.3% sn-2 PA). Infant demographics, feeding status, stool characteristics, physical exams, and stool samples were collected at 6, 16, and 24 weeks. Per-protocol analysis was used. RESULTS: The sn-2 group exhibited a significant time-dependent decline in fecal saponified PA and calcium over time (Ph for Trend < 0.001). The BF group declined faster than the sn-2 group (Padjusted for Group*Time < 0.001). Fecal saponified PA proportion in sn-2 group was significantly lower than controls at all timepoints. At week 24, fecal calcium was lower in the sn-2 group vs. control (0.9 vs. 1.3 mg/g, P = 0.010). No significant difference was found in stool frequency, consistency or size between sn-2 and control groups at any point. CONCLUSION: Infant formula enriched with > 40% sn-2 palmitate reduces fecal fatty acid and calcium excretion, supports efficient lipid and calcium absorption, shows a fecal magnesium pattern similar to breastfed infants, but does not alter stool characteristics relative to the control formula. TRIAL REGISTRATION: The trial is registered at Chinese Clinical Trial Registry: ChiCTR1800014479; 30/Jan./2018.