Nitin R. Mehta

Effect of human milk or formula on gastric function and fat digestion in the premature infant.

The effect of diet, human milk or formula, on gastric function (lipase and pepsin activity, pH, and volume) and intragastric digestion of fat was assessed in 28 appropriate for gestational age preterm infants (gestational age, 28.9 ± 1.4, 29.1 ± 0.9, 29.5 ± 0.6 wk; birth weight, 1.00 ± 0.14 to 1.18 ± 0.07 kg). The infants were fed either human milk (n = 11), SMA Super Preemie formula (n = 9), or Similac, Special Care formula (n = 8). Fasting and postprandial activity of digestive enzymes, pH, and gastric volume (measured before or during 50 min after gavage feeding) did not differ as a function of diet among the three groups of infants. Gastric lipase output, 23.1 ± 5.1, 28.3± 6.6, and 22.5 ± 6.4 (U/kg of body weight) in human milk-, SMA SP-, or Similac SC-fed infants was comparable to the gastric lipase output of healthy adults fed a high fat diet (22.6 ± 3.0). Pepsin output was, however, significantly lower (597 ± 77, 743 ± 97, and 639± 142 U/kg of body weight) in human milk-, SMA SP-, and Similac SC-fed infants) than in healthy adults (3352 ± 753 U/kg). The hydrolysis of dietary fat was 1.7-2.5-fold higher (p < 0.01) in human milk-fed infants than in infants fed either formula. We conclude that differences in type of feeding, i.e. different fatty acid profiles(long chain or medium chain triglycerides), different emulsions (natural or artificial), and different fat particle sizes do not affect the level of activity of gastric enzymes. However, the triglyceride within milk fat globules appears to be more accessible to gastric lipase than that within formula fat particles. We suggest that the contribution of gastric lipase to overall fat digestion might be greater in the newborn (a period of pancreatic insufficiency) than in the adult.

Milk fat globule glycoproteins in human milk and in gastric aspirates of mother's milk-fed preterm infants.

Human milk fat globule (HMFG) glycoproteins can prevent infections by microorganisms in breast-fed infants; the MUC-1 mucin inhibits binding of S-fimbriated Escherchia coli to buccal mucosa, and lactadherin may prevent symptomatic rotavirus infections. In this study, the survival of these HMFG glycoproteins in the stomach of human milk-fed preterm infants (gestational age = 27.5 ± 0.4 wk) was assessed, and levels in their mothers milk determined, using specific RIAs. Butyrophilin, a major component of HMFG membrane that has no demonstrated antimicrobial activity, was studied for comparison. The levels of mucin, lactadherin, and butyrophilin in 41 milk samples of 20 mothers were 729 ± 75, 93 ± 10, and 41 ± 3 µg/mL, respectively. Mucin and lactadherin were significantly higher in early milk samples (<15 d postpartum) than in later milk samples (15-90 d postpartum), whereas butyrophilin showed no such difference. Significant amounts of mucin and lactadherin were found in almost all gastric aspirates of human milk-fed infants, even 4 h after feeding (mucin, 270 ± 30 µg/mL; lactadherin, 23.2 ± 4.4 µg/mL), whereas butyrophilin was rapidly degraded in the majority of aspirates. Western blot analysis demonstrated that the immunoreactive mucin, lactadherin, and butyrophilin in the milk-fed gastric aspirates had the expected native molecular weights. Mucin and lactadherin survived at all gastric pH values, whereas butyrophilin was found only at pH > 4. Neither lactadherin nor butyrophilin were detected in gastric aspirates of formula-fed infants (gestational age = 27.8 ± 0.5 wk), whereas the very low level of mucin (9.1 ± 1.1 µg/mL) in this group is presumably cross-reacting gastric mucin. These results demonstrate that two HMFG glycoproteins implicated in prevention of infection, MUC-1 mucin and lactadherin, survive and maintain their integrity in the stomachs of human milk-fed preterm infants.

The Lipolytic Triad Human Lingual, Breast Milk, and Pancreatic Lipases: Physiological Implications of Their Characteristics in Digestion of Dietary Fats

The characteristics of human lingual, breast milk, and pancreatic lipases as related to the digestion of dietary fats in infants are discussed. The activity and specificity of these enzymes and structure of the dietary fats largely determine the rates of lipolysis, the types of digestion products formed, and the rates of absorption. Also possibly influenced are micelle formation, intestinal health, breast milk jaundice, and the absorption of other nutrients. In premature infants, the action of lingual and breast milk lipase are particularly important in the absorption of dietary fatty acids.

Lipolysis of triglycerides of human milk during storage at low temperatures: a note of caution.

Summary: Human milk samples were divided at collection and stored at −70°C or −20°C, or extracted immediately with organic solvent, to compare lipid class composition. Storage at −20°C was not satisfactory for maintaining milk lipid composition, for it resulted in hydrolysis of triglycerides and the appearance of free fatty acids.

Fat absorption in premature infants: medium-chain triglycerides and long-chain triglycerides are absorbed from formula at similar rates.

Fat absorption from two different premature infant formulas and one full-term formula containing three different fat blends was investigated in two groups of premature infants. The first group of nine infants (gestational age, 29.1 ± 0.88 weeks; postnatal age, 3.13 ± 0.71 weeks) was fed alternately for 1 week each SMA preterm formula containing either high levels (50%) of medium-chain triglycerides (MCT) (6:0, 8:0, and 10:0) or high levels (86%) of long-chain triglycerides (LCT) (≥C12). Except for fat blends, the formulas were otherwise identical. The second group of 11 infants (gestational age, 30.5 ± 0.77 weeks, studied at a postnatal age of 4.33 ± 0.91 weeks) was fed for 1 week a full-term infant formula, S-26, containing 98% LCT. Fat absorption (studied during a 3-day fat balance period) was similar irrespective of fat blend: 89.08 ± 2.37% during feeding of preterm SMA, 50% MCT; 87.0 ± 3.81% during feeding of preterm SMA, 86% LCT: and 83.00 ± 2.89% during feeding of S-26, 98% LCT. Weight gain (grams per day) and increase in length (centimeters per day) were 23.2 ± 1.7, 21.20 ± 1.7, and 14.28 ± 2.9, and 0.17 ± 0.06, 0.16 ± 0.04, and 0.22 ± 0.07 during feeding of the three fat blends, respectively. Lipase activity levels in fasting gastric aspirates were higher during feeding of the LCT than the MCT formula. The possible stimulation of gastric lipase secretion secondary to long-chain fatty acid stimulation of cholecystokinin secretion might be related to the efficient digestion of formula fat, irrespective of triglyceride-fatty acid chain length. The study shows that preterm infants are able to digest and absorb efficiently formula fat containing as much as 98% long-chain fatty acids.

α-amylase in Preterm Human Milk

Summary We have measured α-amylase activity in the milk of 18 women who delivered at 25–40 weeks of pregnancy: 25–30 weeks (n = 7), 31–35 weeks (n = 5), and 36–40 weeks (n = 6). In each subject, α-amylase activity in milk was measured 3 days postpartum (colostrum) and at 1. 3, and 6 weeks of lactation. In each of these three groups, α-amylase activity was high in colostrum (mean values of 8,973 ± 697, 4.422 ± 1.000, and 3,550 ± 889 U/L. respectively) and decreased gradually during the following 6 weeks of lactation (mean values of 2.007 ± 413. 1,462 ± 465, and 1,373 ± 400 U/L, respectively. after 6 weeks). The decrease in total α-amylase activity during this time period was not accounted for by a similar decrease in total milk protein since the specific α-amylase activity in colostrum (142.3 ± 15.9 U/g protein) was substantially greater than that measured in milk obtained 6 weeks postpartum (103.4 ± 12.6 U/g protein). The α-amylase in pooled preterm human milk was relatively stable (22°r loss of activity) when preincubated at a pH of 3.0 for 2 h at 37°C. The activity of the enzyme in preterm human milk had a broad pH optimum in the range of 5.0–7.0. Thus, the enzyme can pass through the stomach of the infant after a milk meal without substantial inactivation because of acidity (pH 3.5–6.5). and has maximum catalytic activity at a pH in the range of that found in the duodenum (pH 6.0–7.0).

Comparison of the cholesteryl ester composition of human milk from preterm and term mothers.

Milk was obtained on postpartum days 2-3 (colostrum) and days 7, 21, 42, and 84 from mothers of 18 very premature (VPT, 26-30 weeks gestational age), 28 premature (PT, 31-36 weeks), and 6 term (T, 37-40 weeks) infants. Lipids were extracted in chloroform-methanol and analyzed by thin-layer (TLC) and gas liquid chromatography (GLC). Fatty acid composition of cholesteryl esters was determined by GLC after isolation of cholesteryl esters by preparative TLC and preparation of methyl esters of the constituent fatty acids. As lactation progressed, amounts of total cholesterol and cholesteryl esters declined. Cholesteryl esters decreased from about 5 mg/dl in colostrum to 1 mg/dl in mature milk. The cholesteryl esters of colostrum from mothers of premature infants were different in fatty acid composition from those of term infants. Proportions of medium-chain saturated fatty acids (12:0, 14:0, 16:0) of preterm colostrum (VPT and PT) were considerably lower than in term colostrum: 23% of total fatty acids versus 35%. Proportions of 18:3, 20:3, and 20:4 of VPT (5.6%) and PT (6.2%) colostrum were considerably higher than T colostrum (1.8%). The fatty acid composition of cholesteryl esters of VPT, PT, and T milk was relatively similar at all subsequent lactation periods. Fatty acids esterified with cholesterol in weight percents were as follows: 10:0, 0.7; 12:0, 2.6; 14:0, 2.3; 16:0, 11.4; 16:1, 5.0; 18:0, 8.8; 18:1, 32.9; 18:2, 30.6; 18:3, 1.7; 20:3, 0.9; and 20:4, 1.8. Unsaturated fatty acids contributed 73 wt % of fatty acids in cholesteryl esters, which is considerably higher than in milk triglycerides. The greatest difference occurred in 18:2 content, which was 30.6% in cholesteryl esters and only 13.0% of total fatty acids in milk. Results suggest that unsaturated fatty acids are associated preferentially with the cholesteryl ester fraction and that the fatty acid composition of cholesteryl esters differs from the composition of total milk lipid.

Bile salt-stimulated lipase of human milk: characteristics of the enzyme in the milk of mothers of premature and full-term infants

Human milk contains a lipase (bile salt-stimulated lipase) that is considered to have an important role in infant fat digestion. In this study we compared the characteristics of bile salt-stimulated lipase activity in milk samples from mothers delivering prematurely (26-30 and 31-37 weeks of gestation) and in milk from mothers delivering at term (38-42 weeks of gestation). Preterm milks were collected at day 1-5 and during week 6 of lactation. Term milks were collected during week 6 of lactation. The characteristics of the enzyme (kinetics, enzyme concentration, pH optimum, and pH stability, effects of bile salt structure and concentration, eserine inhibition) were identical regardless of length of pregnancy or duration of lactation. Bile salt-stimulated lipase had a neutral to alkaline pH optimum (pH 7.3-8.6), was stable for 1 h at a wide pH range (pH 3.1-8.6), was active only in the presence of primary bile salts, and was inhibited by eserine. The data indicate that, following parturition at as early as 26 weeks of gestation, the mammary glands synthesizes bile salt-stimulated lipase with identical characteristics as does the mammary gland after a full-term pregnancy.

Adherence of medium-chain fatty acids to feeding tubes of premature infants fed formula fortified with medium-chain triglyceride

Summary: Adherence of medium-chain triglyceride (MCT) oil to feeding tubes during gavage feeding of Enfamil formula was quantitated. Infants were fed similar volumes of either unfortified formula (n = 11) or MCT oil-fortified formula (0.5 ml/oz); either the MCT oil was mixed with the formula before feeding (n = 11) or the MCT oil was delivered into the feeding tube and then was followed by formula (n = 11). The fat residue in the feeding sets was quantitated by gravimetry, and individual fatty acids were characterized by gas-liquid chromatography. The data show that only trace amounts of lipid (0.23 ± 0.04%) adhered to feeding sets during feeding of unfortified formula. Significantly more lipid (p < 0.0005) adhered when formula was fortified with MCT oil, and the method of feeding greatly affected lipid adherence, i.e., 1.52 ± 0.21% when the MCT oil was followed by formula versus 10.20 ± 1.76% when the MCT oil was mixed with formula before feeding. Analysis of the fat residue of fortified formula showed that >90% was composed of C8:0 and C10:0, the major fatty acid components of MCT oil. We suggest that care be exercised when fortifying infant formula with MCT oil.

Gastric Proteolysis in the Preterm Infant: Protein Digestion is Limited and Is Not Affected by Diet, Human Milk or Formula † 580

Gastric Proteolysis in the Preterm Infant: Protein Digestion is Limited and Is Not Affected by Diet, Human Milk or Formula † 580