Fat Malabsorption in Preterm and Term Neonates Is Not Due to Insufficient Lipolysis, but to Impaired Uptake of Long Chain Fatty Acids from the Intestinal Lumen

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Abstract 1706 Neonatal Nutrition and Metabolism II Poster Symposium, Monday, 5/3

Background: In human neonates, especially in preterms, the intestinal absorption of dietary fat is impaired until the postnatal age of 6 months. Although it has been demonstrated that (preterm) neonates have an immature production of pancreatic fluid and of bile, it is not known whether this fat malabsorption is primarily due to insufficient lipolysis or to impaired uptake of long chain fatty acids. We aimed to determine in humans in vitro the role of lipolysis and of uptake of long chain fatty acids in neonatal fat absorption in a longitudinal fashion.

Design: In 16 preterm and in 8 term neonates intestinal lipolysis and uptake of long chain fatty acids were determined at 4 (preterms) or 3 consecutive timepoints between birth and 6 months after the term age. Lipolysis was determined by measuring serum concentration of 1-13C-palmitic acid (PA) after the enteral administration of tri-1-13C palmitoyl-glycerol. Intestinal uptake of long chain fatty acids per se (i.e. independent from lipolysis) was determined by measuring serum concentration of 1-13C-stearic acid (SA) after enteral administration of this fatty acid. We reasoned that, if lipolysis would be rate-limiting for fat absorption, the PA absorption, but not the SA absorption, would be positively correlated with the 72h-fat absorption percentage (%FA, calculated from fat ingested by formula feeding and fat excreted via feces). Alternatively, if impaired uptake of long chain fatty acid per se would be responsible for neonatal fat malabsorption, both PA absorption and SA absorption would be expected to correlate positively with %FA.

Results: The efficacy of fat absorption increased linearly in preterm and term infants: from 88.7 ± 5.3% at 32.6 wk postconceptional age (PCA), to 97.3 ± 2.3% (53.6 wk PCA); and from 91.7 ± 2.3% (40.4 wk PCA) to 96.5 ± 3.0% (59.4 wk PCA), respectively. In individual infants, the 4h-serum concentrations of PA and of SA increased linearly between the first postnatal timepoint and the timepoint 6 months after term age. Upon pooling of the individual data, the 4h-serum concentration of SA, as well as that of PA, appeared highly correlated with the %FA (R = 0.90, P = 0.006; and, R = 0.83, P= 0.02; respectively).

Conclusion: Neonatal fat malabsorption, both in preterm and in term infants, is mainly due to impaired uptake of long chain fatty acids from the intestinal lumen.

Study was supported by a grant from Numeco BV, The Netherlands

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