Background Levels of Carbon-13 Reduced in Breath and Stool by New Infant Formula

Abstract

Summary: Studies of the absorption and bioavailability of nutrients naturally enriched with ¹³C require accurate measurements of small increases of ¹³C in respiratory CO₂ and stool carbon. The sensitivity of these measurements would be increased if the natural background of ¹³C in these exereta were reduced. We have developed a ¹³C-depleted infant formula based on lactose, whey, and casein from New Zealand cows that consume only C₃ vegetation naturally low in ¹³C. This formula, designated CNRC₃ was produced by a commercial infant formula manufacturer and was comparable with a 60:40 whey/casein product. To test the ability of the formula to reduce baseline levels of ¹³C in infant excreta, 10 formulafed infants 28–60 days old and free of metabolic disorders were enrolled in the 9-day study. Two stool samples were collected daily. Infants received their usual formula on days 1 and 2 and were switched to CNRC₃ formula for days 3–9. On days 2 and 9, seven breath samples were collected at 30-min intervals with a face mask. Breath and stool samples were analyzed for ¹³C content by gas isotope ratio mass spectrometry. Infants consuming their commercial formula had breath × ¹³C values of −21.1 × 0.6%, over the 3-h collection period; stool values were −22.9 × 0.4%. After 7 days on the CNRC₃ formula, ¹³C values of breath declined by 5.6% to −26.7 × 0.7%; stool values declined by 3.0% to −25.6 × 0.5%. The reduced background of ¹³C achieved by the CNRC₃ formula can improve resolution of excess ¹³C from naturally enriched substrates in infant breath by ~50% and in stool by ~30%