Quantitative and qualitative study of gastric lipolysis in premature infants: do MCT-enriched infant formulas improve fat digestion?

Fatty acid composition and phospholipid types used in infant formulas modifies the establishment of human gut bacteria in germ-free mice

Human milk fat contains high concentrations of medium-chained fatty acids (MCFA) and triacylglycerols emulsified by a sphingomyelin-rich phospholipid membrane (milk phospholipids, MPL). Infant formula comprises mainly long-chained fatty acids (LCFA) emulsified with dairy proteins and soy lecithin (SL) lacking sphingomyelin. Sphingomyelin content and saturation level of phospholipids affect the gut lipase activity, which alters the concentrations of lipid hydrolysis products in ileum and colon, and hereby putatively affects the competitive advantage of specific gut bacteria. Thus, differences in phospholipid and FA composition may modulate the establishment of the gut microbiota. We investigated effects of fatty acid (FA) composition and emulsification (MPL vs SL) ingested during establishment of human gut microbiota in germ-free mice, and found that cecal microbiotas from mice given MCFA-rich emulsions were characterized by high relative abundances of Bacteroidaceae and Desulfovibrionaceae, while LCFA-rich emulsions caused higher abundances of Enterobacteriaceae, Erysipelotrichaceae, Coriobacteriaceae and Enterococcaceae. Consumption of SL-emulsified lipids skewed the community towards more Enterococcaceae and Enterobacteriaceae, while MPL increased Bacteroidaceae, Desulfovibrionaceae, Rikkenellaceae and Porphyromonadaceae. Intake of SL increased cecal concentrations of iso-valeric and iso-butyric acids. This suggests that fat-type and emulsifiers applied in infant formula may have distinct effects on the establishment of the gut microbiota in formula-fed infants.

Guidance on the risk assessment of substances present in food intended for infants below 16 weeks of age

Following a request from the European Commission to EFSA, the EFSA Scientific Committee (SC) prepared a guidance for the risk assessment of substances present in food intended for infants below 16 weeks of age. In its approach to develop this guidance, the EFSA SC took into account, among others, (i) an exposure assessment based on infant formula as the only source of nutrition; (ii) knowledge of organ development in human infants, including the development of the gut, metabolic and excretory capacities, the brain and brain barriers, the immune system, the endocrine and reproductive systems; (iii) the overall toxicological profile of the substance identified through the standard toxicological tests, including critical effects; (iv) the relevance for the human infant of the neonatal experimental animal models used. The EFSA SC notes that during the period from birth up to 16 weeks, infants are expected to be exclusively fed on breast milk and/or infant formula. The EFSA SC views this period as the time where health-based guidance values for the general population do not apply without further considerations. High infant formula consumption per body weight is derived from 95th percentile consumption. The first weeks of life is the time of the highest relative consumption on a body weight basis. Therefore, when performing an exposure assessment, the EFSA SC proposes to use the high consumption value of 260 mL/kg bw per day. A decision tree approach is proposed that enables a risk assessment of substances present in food intended for infants below 16 weeks of age. The additional information needed when testing substances present in food for infants below 16 weeks of age and the approach to be taken for the risk assessment are on a case-by-case basis, depending on whether the substance is added intentionally to food and is systemically available.

Impact of human milk pasteurization on gastric digestion in preterm infants: a randomized controlled trial

BACKGROUND

Holder pasteurization has been reported to modify human milk composition and structure by inactivating bile salt-stimulated lipase (BSSL) and partially denaturing some of its proteins, potentially affecting its subsequent digestion.

OBJECTIVE

We sought to determine the impact of human milk pasteurization on gastric digestion (particularly for proteins and lipids) in preterm infants who were fed their mothers' own milk either raw or pasteurized.

DESIGN

In a randomized controlled trial, 12 hospitalized tube-fed preterm infants were their own control group in comparing the gastric digestion of raw human milk (RHM) with pasteurized human milk (PHM). Over a 6-d sequence, gastric aspirates were collected 2 times/d before and after RHM or PHM ingestion. The impact of milk pasteurization digestive kinetics and disintegration was tested with the use of a general linear mixed model.

RESULTS

Despite inactivating BSSL, instantaneous lipolysis was not affected by pasteurization (mean ± SD at 90 min: 12.6% ± 4.7%; P > 0.05). Lipolysis occurred in milk before digestion and was higher for PHM than for RHM (mean ± SD: 3.2% ± 0.6% and 2.2% ± 0.8%, respectively; P < 0.001). Pasteurization enhanced the proteolysis of lactoferrin (P < 0.01) and reduced that of α-lactalbumin (only at 90 min) (P < 0.05). Strong emulsion destabilization was observed, with smaller aggregates and a higher specific surface for PHM (P < 0.05). Pasteurization did not affect gastric emptying (∼30-min half time) or pH (mean ± SD: 4.4 ± 0.8) at 90 min.

CONCLUSIONS

Overall, pasteurization had no impact on the gastric digestion of lipids and some proteins from human milk but did affect lactoferrin and α-lactalbumin proteolysis and emulsion disintegration. Freeze-thawing and pasteurization increased the milk lipolysis before digestion but did not affect gastric lipolysis. Possible consequences on intestinal digestion and associated nutritional outcomes were not considered in this study. This trial was registered at clinicaltrials.gov as NCT02112331.

In Vitro Model Simulating Gastro-Intestinal Digestion in the Pediatric Population (Neonates and Young Infants)

The focus on drug delivery for the pediatric population has been steadily increasing in the last decades. In terms of developing in vitro models simulating characteristics of the targeted pediatric population, with the purpose of predicting drug product performance after oral administration, it is important to simulate the gastro-intestinal conditions and processes the drug will encounter upon oral administration. When a drug is administered in the fed state, which is commonly the case for neonates, as they are typically fed every 3 h, the digestion of the milk will affect the composition of the fluid available for drug dissolution/solubilization. Therefore, in order to predict the solubilized amount of drug available for absorption, an in vitro model simulating digestion in the gastro-intestinal tract should be utilized. In order to simulate the digestion process and the drug solubilization taking place in vivo, the following aspects should be considered; physiologically relevant media, media volume, use of physiological enzymes in proper amounts, as well as correct pH and addition of relevant co-factors, e.g., bile salts and co-enzymes. Furthermore, physiological transit times and appropriate mixing should be considered and mimicked as close as possible. This paper presents a literature review on physiological factors relevant for digestion and drug solubilization in neonates. Based on the available literature data, a novel in vitro digestion model simulating digestion and drug solubilization in the neonate and young infant pediatric population (2 months old and younger) was designed.

The impact of lactoferrin with different levels of metal saturation on the intestinal epithelial barrier function and mucosal inflammation

Translocation of bacteria, primarily Gram-negative pathogenic flora, from the intestinal lumen into the circulatory system leads to sepsis. In newborns, and especially very low birth weight infants, sepsis is a major cause of morbidity and mortality. The results of recently conducted clinical trials suggest that lactoferrin, an iron-binding protein that is abundant in mammalian colostrum and milk, may be an effective agent in preventing sepsis in newborns. However, despite numerous basic studies on lactoferrin, very little is known about how metal saturation of this protein affects a host’s health. Therefore, the main objective of this study was to elucidate how iron-depleted, iron-saturated, and manganese-saturated forms of lactoferrin regulate intestinal barrier function via interactions with epithelial cells and macrophages. For these studies, a human intestinal epithelial cell line, Caco-2, was used. In this model, none of the tested lactoferrin forms induced higher levels of apoptosis or necrosis. There was also no change in the production of tight junction proteins regardless of lactoferrin metal saturation status. None of the tested forms induced a pro-inflammatory response in Caco-2 cells or in macrophages either. However, the various lactoferrin forms did effectively inhibit the pro-inflammatory response in macrophages that were activated with lipopolysaccharide with the most potent effect observed for apolactoferrin. Lactoferrin that was not bound to its cognate receptor was able to bind and neutralize lipopolysaccharide. Lactoferrin was also able to neutralize microbial-derived antigens, thereby potentially reducing their pro-inflammatory effect. Therefore, we hypothesize that lactoferrin supplementation is a relevant strategy for preventing sepsis.

Relevant pH and lipase for in vitro models of gastric digestion

The development of in vitro digestion models relies on the availability of in vivo data such as digestive enzyme levels and pH values recorded in the course of meal digestion. The variations of these parameters along the GI tract are important for designing dynamic digestion models but also static models for which the choice of representative conditions of the gastric and intestinal conditions is critical. Simulating gastric digestion with a static model and a single set of parameters is particularly challenging because the variations in pH and enzyme concentration occurring in the stomach are much broader than those occurring in the small intestine. A review of the literature on this topic reveals that most models of gastric digestion use very low pH values that are not representative of the fed conditions. This is illustrated here by showing the variations in gastric pH as a function of meal gastric emptying instead of time. This representation highlights those pH values that are the most relevant for testing meal digestion in the stomach. Gastric lipolysis is still largely ignored or is performed with microbial lipases. In vivo data on gastric lipase and lipolysis have however been collected in humans and dogs during test meals. The biochemical characterization of gastric lipase has shown that this enzyme is rather unique among lipases: (i) stability and activity in the pH range 2 to 7 with an optimum at pH 4-5.4; (ii) high tensioactivity that allows resistance to bile salts and penetration into phospholipid layers covering TAG droplets; (iii) sn-3 stereospecificity for TAG hydrolysis; and (iv) resistance to pepsin. Most of these properties have been known for more than two decades and should provide a rational basis for the replacement of gastric lipase by other lipases when gastric lipase is not available.

Medium chain triglycerides (MCT) formulas in paediatric and allergological practice

Fats constitute the most significant nutritional source of energy. Their proper use by the body conditions a number of complex mechanisms of digestion, absorption, distribution, and metabolism. These mechanisms are facilitated by fats made of medium chain fatty acids; therefore, they are an easy and quick source of energy. Thus, an increased supply of medium chain triglycerides (MCT) is particularly important in patients with disturbances of digestion and absorption such as disturbed bile secretion, classic coeliac disease, short bowel syndrome, inflammatory diseases of the intestines, disturbed outflow of lymph, some metabolic disease, and severe food allergies, as well as in prematurely born neonates. Use of preparations containing an additive of MCT is limited, especially if they are to be used for a longer period of time. With a large quantity of MCT in a diet, there is a risk of deficiency of necessary unsaturated fatty acids and some fat-soluble vitamins. The caloricity of MTC compared to long-chain triglycerides is lower, and formulas with MCT are characterised by higher osmolality. Medium chain triglycerides is not recommended as an additive to standard formulas for healthy children. The use of MCT should be limited to strictly specified medical indications.

Dicarboxylic Acid Excretion in Normal Formula-Fed and Breastfed Infants

PURPOSE

Infant formulas are often supplemented with medium-chain triglycerides (MCTs) to optimize calories for small for gestational age or preterm infants. High amounts of MCTs have been associated with an increase in dicarboxylic acid (DCA) in the urine. Elevated DCA in the urine is also a clinical indicator for fatty acid metabolism disorders. The purpose of this study was to identify if there is an amount of MCTs that can be provided without elevating urinary DCA excretion.

METHODS

A metabolic screening laboratory provided urinary DCA excretion data for 175 infants. It was verified that no infants were diagnosed with metabolic disorders and therefore were considered "metabolically normal." All infants were either formula fed or breastfed at the time of screening. The type and volume of formula provided at the time of urine screening was documented. The exact amount of MCTs provided to each infant was calculated.

RESULTS

The mean age of the infants was 3.09 months. The mean total DCA was determined for both the breastfeeding and formula groups. Within the formula group, the means were 32.07, 13.36, and 5.77 mmol/mol creatinine for adipic, suberic, and sebacic acids, respectively. Spearman correlation coefficient indicated correlations of r = 0.0693, r = 0.0166, and r = -0.0128 between percent MCT and adipic, suberic, and sebacic acids, respectively. No value was statistically significant. DCA excretion amounts did not vary between breastfed and formula-fed infants. Our data suggest that clinicians should not expect elevated dicarboxylic aciduria in infants who are fed a standard formula without added MCT oil.

Lipid hydrolysis products affect the composition of infant gut microbial communities in vitro

Some lipid hydrolysis products such as medium-chained NEFA (MC-NEFA), sphingosine and monoacylglycerols (MAG) possess antibacterial activity, while others, including oleic acid, are essential for the optimal growth of Lactobacillus species. Thus, changes in the concentrations of NEFA and MAG in the distal ileum and colon can potentially selectively modulate the composition of the gut microbiota, especially in early life when lipid absorption efficacy is reduced. As medium-chained fatty acids are enriched in mothers' milk, such effects may be highly relevant during gut colonisation. In the present study, we examined the effect of selected NEFA, MAG and sphingosine on the composition of faecal microbial communities derived from infants aged 2-5 months during a 24 h anaerobic in vitro fermentation. We tested lipid mixtures in the concentration range of 0-200 μm, either based on MC-NEFA (10 : 0 to 14 : 0 and MAG 12 : 0) or long-chained NEFA (LC-NEFA; 16 : 0 to 18 : 1 and MAG 16 : 0) with and without sphingosine, representing lipid hydrolysis products characteristic for intestinal hydrolysis of breast milk lipids. Ion Torrent sequencing of the bacterial 16S ribosomal RNA gene revealed that the relative abundance of lactic acid-producing genera, including Lactobacillus and Bifidobacterium, was generally increased in the presence of 50 μm or higher concentrations of MC-NEFA. For Bifidobacterium, the same effect was also observed in the presence of a mixture containing LC-NEFA with sphingosine. On the contrary, the relative abundance of Enterobacteriaceae was significantly decreased in the presence of both lipid mixtures. Our findings suggest that the high concentration of medium-chained fatty acids in breast milk might have functional effects on the establishment of the gut microbiota in early life.

[Expert consensus on the nutritional aspects of initial and follow-on infant formulas]

INTRODUCTION

Infant feeding in the first months/years of life affects the health in the short and long term. Breastfeeding is the perfect food due to its many benefits. However, when breastfeeding is not possible, infant formulas are the best alternative. The aim of this study is to define the role of the supplemented formulas in infant nutrition using the opinion of a panel of experts in infant gastroenterology and nutrition.

MATERIAL AND METHODS

A survey, using 62 items, stratified into 5 blocks, was performed by 48 panelists using the Delphi method to achieve a professional criteria consensus on nutritional aspects of infant formulas.

RESULTS

A consensus was reached in 64.6% of the items, with a non-unified agreement being established as regards the nutritional aspects of infant formulas, and their influence in body and brain development and immune maturity.

CONCLUSIONS

According to the experts surveyed, there is consensus as regards the suitable composition of lipids, lactose, calcium, vitamin D, and prebiotics in infant formulas, for a correct cerebral, immune and somatic development. There was no consensus on the not yet well-defined subjects, such as nutritional quality of proteins, use of thickeners, taurine supplementation, probiotic, and symbiotic aspects. More studies are necessary to confirm these subjects.

The structure of infant formulas impacts their lipolysis, proteolysis and disintegration during in vitro gastric digestion

Milk lipids supply most of the calories necessary for newborn growth in maternal milk or infant formulas. The chemical composition of infant formulas has been optimized but not the structure of the emulsion. There is still a major difference between the native emulsions of milk fat globules and processed submicronic emulsions in infant formulas. This difference may modify the kinetics of digestion of emulsions in newborns and influence lipid metabolism. To check this, semi-dynamic gastric in vitro digestions were conducted on three matrices: a standardized milk emulsion containing native milk fat globules referred to as minimally-processed emulsion and two processed model infant formulas (homogenized or homogenized/pasteurized). Gastric conditions mimicked those reported in newborns. The minimally-processed emulsion was lipolyzed and proteolyzed slower than processed formulas. The difference in initial structure persisted during digestion. The surface of the droplets was the key parameter to control gastric lipolysis kinetics, the pattern of released fatty acids and proteolysis by faster hydrolysis of adsorbed proteins.

Specificity of infant digestive conditions: some clues for developing relevant in vitro models

Digestion of nutrients is an essential function of the newborn infant gut to allow growth and development and understanding infant digestive function is essential to optimize nutrition and oral drug delivery. Ethical considerations prohibit invasive in vivo trials and as a consequence in vitro assays are often conducted. However, the choice of in vitro model parameters are not supported by an exhaustive analysis of the literature and do not mimic precisely the digestive conditions of the infant. This review contains a compilation of the studies which characterized the gastroduodenal conditions in full-term or preterm infants of variable postnatal age from birth up to six months. Important data about healthy full-term infants are reported. The enzymatic (type of enzymes and level of activity) and nonenzymatic (milk-based diet, frequency of feeding, bile salt concentrations) conditions of digestion in infants are shown to differ significantly from those in adults. In addition, the interindividual and developmental variability of the digestive conditions in infants is also highlighted.

Gastric digestion of α-lactalbumin in adult human subjects using capsule endoscopy and nasogastric tube sampling

In the present study, structural changes in the milk protein α-lactalbumin (α-LA) and its proteolysis were investigated for the potential formation of protein-fatty acid complexes during in vivo gastric digestion. Capsule endoscopy allowed visualisation of the digestion of the test drinks, with nasogastric tubes allowing sampling of the gastric contents. A total of ten healthy volunteers had nasogastric tubes inserted into the stomach and ingested test drinks containing 50 g/l of sucrose and 25 g/l of α-LA with and without 4 g/l of oleic acid (OA). The samples of gastric contents were collected for analysis at 3 min intervals. The results revealed a rapid decrease in the pH of the stomach of the subjects. The fasting pH of 2·31 (SD 1·19) increased to a pH maxima of pH 6·54 (SD 0·29) after ingestion, with a subsequent decrease to pH 2·22 (SD 1·91) after 21 min (n 8). Fluorescence spectroscopy and Fourier transform IR spectroscopy revealed partial protein unfolding, coinciding with the decrease in pH below the isoelectric point of α-LA. The activity of pepsin in the fasting state was found to be 39 (SD 12) units/ml of gastric juice. Rapid digestion of the protein occurred: after 15 min, no native protein was detected using SDS-PAGE; HPLC revealed the presence of small amounts of native protein after 24 min of gastric digestion. Mirocam® capsule endoscopy imaging and video clips (see the online supplementary material) revealed that gastric peristalsis resulted in a heterogeneous mixture during gastric digestion. Unfolding of α-LA was observed during gastric transit; however, there was no evidence of a cytotoxic complex being formed between α-LA and OA.

Clinical, molecular and functional investigation on an infant with neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD)

BACKGROUND AND OBJECTIVE

SLC25A13 analysis has provided reliable evidences for the definitive diagnosis of citrin deficiency (CD) in the past decade. Meanwhile, these studies generated some issues yet to be resolved, including the pathogenicity of SLC25A13 missense mutations and the mRNA product from the mutation c.615+5G>A. This study aims to investigate the effect of a novel missense mutation on the aspartate/glutamate carrier (AGC) function of citrin protein, and to explore the aberrant transcript from c.615+5G>A in the same CD infant.

METHODS AND RESULTS

By means of screening for prevalent SLC25A13 mutations and exons sequencing, the patient proved a compound heterozygote of c.615+5G>A and a novel c.1064G>A (p.Arg355Gln) mutation. An aberrant transcript with retention of the entire intron 6, r.[615+1_615+1789ins; 615+5 g>a] (GenBank accession number KJ128074), which was resulted from c.615+5G>A, was detected by RT-PCR and cDNA sequencing. After bioinformatic analyses of the novel missense mutation c.1064G>A, the growth abilities of three agc1Δ yeast strains were tested, which had been transformed with recombinant or empty vectors, respectively. Besides the bioinformatically pathogenic evidences, the growth ability of the agc1Δ strains transformed with mutant recombinant was the same as with empty vector, but significantly lower than that with normal control in functional analysis.

CONCLUSIONS

A CD infant was definitely diagnosed in this paper by a genetic, transcriptional and functional analysis of SLC25A13 gene. This study provided direct laboratory evidences supporting the splice-site nature of the c.615+5G>A mutation, and the novel c.1064G>A variation, which proved a pathogenic mutation bioinformatically and functionally, enriched the SLC25A13 mutation spectrum.

In vitro digestion of citric acid esters of mono- and diglycerides (CITREM) and CITREM-containing infant formula/emulsions

The GI lipolysis of CITREM is investigated for the first time using various digestive lipases and a two-stepin vitrodigestion model.

Pancreatic lipase-related protein 2 digests fats in human milk and formula in concert with gastric lipase and carboxyl ester lipase

BACKGROUND

Dietary fats must be digested into fatty acids and monoacylglycerols prior to absorption. In adults, colipase-dependent pancreatic triglyceride lipase (PTL) contributes significantly to fat digestion. In newborn rodents and humans, the pancreas expresses low levels of PTL. In rodents, a homologue of PTL, pancreatic lipase-related protein 2 (PLRP2), and carboxyl ester lipase (CEL) compensate for the lack of PTL. In human newborns, the role of PLRP2 in dietary fat digestion is unclear. To clarify the potential of human PLRP2 to influence dietary fat digestion in newborns, we determined PLRP2 activity against human milk and infant formula.

METHODS

The activity of purified recombinant PLRP2, gastric lipase (GL), and CEL against fats in human milk and formula was measured with each lipase alone and in combination with a standard pH-stat assay.

RESULTS

Colipase added to human milk stimulated fat digestion. PLRP2 and CEL had activity against human milk and formula. Predigestion with GL increased PLRP2 activity against both substrates. Together, CEL and PLRP2 activity was additive with formula and synergistic with human milk.

CONCLUSION

PLRP2 can digest fats in human milk and formula. PLRP2 acts in concert with CEL and GL to digest fats in human milk in vitro.

Molecular mechanisms of the cytotoxicity of human α-lactalbumin made lethal to tumor cells (HAMLET) and other protein-oleic acid complexes

Although HAMLET (human α-lactalbumin made lethal to tumor cells), a complex formed by human α-lactalbumin and oleic acid, has a unique apoptotic activity for the selective killing of tumor cells, the molecular mechanisms of expression of the HAMLET activity are not well understood. Therefore, we studied the molecular properties of HAMLET and its goat counterpart, GAMLET (goat α-lactalbumin made lethal to tumor cells), by pulse field gradient NMR and 920-MHz two-dimensional NMR techniques. We also examined the expression of HAMLET-like activities of complexes between oleic acid and other proteins that form a stable molten globule state. We observed that both HAMLET and GAMLET at pH 7.5 were heterogeneous, composed of the native protein, the monomeric molten globule-like state, and the oligomeric species. At pH 2.0 and 50 °C, HAMLET and GAMLET appeared in the monomeric state, and we identified the oleic acid-binding site in the complexes by two-dimensional NMR. Rather surprisingly, the binding site thus identified was markedly different between HAMLET and GAMLET. Furthermore, canine milk lysozyme, apo-myoglobin, and β2-microglobulin all formed the HAMLET-like complex with the anti-tumor activity, when the protein was treated with oleic acid under conditions in which their molten globule states were stable. From these results, we conclude that the protein portion of HAMLET, GAMLET, and the other HAMLET-like protein-oleic acid complexes is not the origin of their cytotoxicity to tumor cells and that the protein portion of these complexes plays a role in the delivery of cytotoxic oleic acid molecules into tumor cells across the cell membrane.

Digested formula but not digested fresh human milk causes death of intestinal cells in vitro: implications for necrotizing enterocolitis

BACKGROUND

Premature infants fed formula are more likely to develop necrotizing enterocolitis (NEC) than those who are breastfed, but the mechanisms of intestinal necrosis in NEC and protection by breast milk are unknown. We hypothesized that after lipase digestion, formula, but not fresh breast milk, contains levels of unbound free fatty acids (FFAs) that are cytotoxic to intestinal cells.

METHODS

We digested multiple term and preterm infant formulas or human milk with pancreatic lipase, proteases (trypsin and chymotrypsin), lipase + proteases, or luminal fluid from a rat small intestine and tested FFA levels and cytotoxicity in vitro on intestinal epithelial cells, endothelial cells, and neutrophils.

RESULTS

Lipase digestion of formula, but not milk, caused significant death of neutrophils (ranging from 47 to 99% with formulas vs. 6% with milk) with similar results in endothelial and epithelial cells. FFAs were significantly elevated in digested formula vs. milk and death from formula was significantly decreased with lipase inhibitor pretreatment, or treatments to bind FFAs. Protease digestion significantly increased FFA binding capacity of formula and milk but only enough to decrease cytotoxicity from milk.

CONCLUSION

FFA-induced cytotoxicity may contribute to the pathogenesis of NEC.

Development of the Digestive System-Experimental Challenges and Approaches of Infant Lipid Digestion

At least during the first 6 months after birth, the nutrition of infants should ideally consist of human milk which provides 40–60 % of energy from lipids. Beyond energy, human milk also delivers lipids with a specific functionality, such as essential fatty acids (FA), phospholipids, and cholesterol. Healthy development, especially of the nervous and digestive systems, depends fundamentally on these. Epidemiological data suggest that human milk provides unique health benefits during early infancy that extend to long-lasting benefits. Preclinical findings show that qualitative changes in dietary lipids, i.e., lipid structure and FA composition, during early life may contribute to the reported long-term effects. Little is known in this respect about the development of digestive function and the digestion and absorption of lipids by the newborn. This review gives a detailed overview of the distinct functionalities that dietary lipids from human milk and infant formula provide and the profound differences in the physiology and biochemistry of lipid digestion between infants and adults. Fundamental mechanisms of infant lipid digestion can, however, almost exclusively be elucidated in vitro. Experimental approaches and their challenges are reviewed in depth.

Lipid digestion and absorption in early life: an update

PURPOSE OF REVIEW

To highlight our understanding of digestion and absorption of dietary lipids in newborn infants, and specifically how these processes differ from those in children and adults.

RECENT FINDINGS

The intestinal concentration of pancreatic triglyceride lipase (PTL) and bile salts is lower in newborns compared to later in life. Instead the PTL-related protein 2 and bile salt-stimulated lipase (BSSL) are the key enzymes secreted from pancreas, which in concerted action with gastric lipase operate to achieve efficient fat absorption during infancy. BSSL is also present in human milk which affects fat absorption and growth in breast-fed preterm infants. Under conditions of low luminal bile salt concentrations fat absorption is likely to occur from liquid crystalline product phases, which may result in absorption from an extended part of the small intestinal mucosal surfaces compared to adults. Chylomicron assembly and secretion also seem to adapt to the specific situation of the newborn.

SUMMARY

Both fat digestion and product absorption are different in newborn infants compared to adults; other lipases are used for digestion and different physical-chemical phases may be used for product absorption. Why these differences occur is still an unsolved question of considerable importance to neonatal nutrition.