This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Enfamil and Enfamil Lipil are rich in palm olein, with a fat blend comprised on 40% palmitic acid and 43% oleic acid. However, in contrast to human milk, the palmitic acid in vegetable oils is predominantly esterified in the sn-1 and sn-3 position rather than the sn-2 position (1), as is the case for palmitic acid found in human milk (2,3). Palmitic acid that is esterified in the sn-1 and sn-3 position tends to be hydrolyzed during digestion and made available to form insoluble calcium soaps, resulting in poorer fat and calcium absorption than is seen with formulas with less palmitic in the sn- 1 and sn-3 position (4-6). Whether the inclusion of interesterified palm olein (with greater palmitic acid in the sn-2 position) in an Enfamil formulation would results in better fat and calcium absorption than the current formulation is not known. Moreover, whether calcium absorption in the current Enfamil formulation is similar to that provided by human milk has not been studied directly. The formula on the market now, like many infant formulas, has the palmitic acid predominantly esterified in the sn-1 and sn-3 position rather than the sn-2 position, as is the case for palmitic acid found in human milk. The second formula has more palmitic acid in the sn-2 position (less in the sn-1 and sn-3 positions), making it more comparable to human milk. As it is even closer in composition to human milk, we consider it to be a safe product and are merely assessing the effect on calcium absorption. From an FDA level, this change is considered minor and does not, for example, require the full set of research studies to allow the change as would be needed for a major change. Finally, previous tolerance studies have been done to demonstrate the safety of the formula. Since modifications and improvements of formulations have been guided by the nutrient content and functional nutrient composition of human milk, it is important that Mead Johnson Nutritionals (MJN) confirm the functional adequacy of Enfamil Lipil compared to human milk. The mean published absorption of calcium from breast milk is 58 +/- 17% with a mean calcium content of 41 mg/100 kcal, yielding a daily calcium absorption of 24.6 +/- 15 (SD) mg/100 kcal. The higher calcium content of Enfamil (78 mg/100 kcal) actually compensates for less fractional calcium absorption (38 +/- 16%). Therefore daily calcium absorption is 29.6 +/- 12.5 mg/100 kcal. All of these values reflect values generated using classic balance techniques rather than dual stables isotopes. Previous studies have shown that by using dual isotope absorption methods we can expect SD for Enfamil Lipil of 8 rather than 12.5 and SD values for Enfamil Lipil with interesterified palm olein fat blend (IPO-EL) of about 40 +/- 10. In contrast to formula, human milk calcium content also varies significantly between mothers in addition to variation in measured fractional absorption, which would be expected to be more similar between groups. Thus, the wider classical balance for absolute calcium absorption from human milk was pooled with the estimated double isotope method variance from the formulas (standard deviations of 15, 8, and 10) to estimate the population variance of 11.4 to calculate the n needed for this study to provide 80% power with an alpha level of 0.05.
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