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15th
World Congress Clinical Nutrition
19th
– 22nd September 2010 El Sokhna Resort - Egypt
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Copyright © 2010.
WCCN2010.COM
All rights reserved |
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Gastrointestinal development –
Implications for feeding infants
Robert Shulman, Baylor College of
Medicine, Houston, Texas, USA
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Objective: Appropriate feedings for
preterm and term infants should be
based, in part, on the ability of
the gastrointestinal tract to digest
and absorb the feeding. Factors
affecting these two processes
include gastrointestinal anatomy
(for example: gastrointestinal
growth and the site of absorption)
and the developmental profile of the
pathways involved in carbohydrate,
protein, and fat digestion and
absorption. The attendees will be
able to discuss the role of these
factors in designing appropriate
feeding regimens for preterm and
term infants as well as the role of
some gastrointestinal hormones in
regulating gastrointestinal growth,
motility, and appetite regulation.
Summary: Gastrointestinal linear
growth is most rapid during the last
trimester of pregnancy.
Gastrointestinal surface area also
is increased by an increase in gut
diameter with a large increase in
surface area occurring from birth to
6 months of age. The increase in
surface area is related, in part, to
enteral feeding. Iron, calcium, and
folate normally are absorbed in the
duodenum and proximal jejunum.
Carbohydrates, protein, and fat
normally are absorbed in the
duodenum and throughout the jejunum.
In contrast, cobalamin and bile
acids are absorbed primarily in the
distal ileum. Pancreatic amylase
activity is minimal until after term
birth. Lactase activity increases
most dramatically in the last
trimester. Glucoamylase and
sucrase-isomaltase activities are
well developed by birth. These
developmental differences in enzyme
activity strongly reflect on the
ability of infants to assimilate
starches, lactose, and glucose
polymers, respectively. Pancreatic
proteases and brush border proteases
are well developed even in very
preterm infants. Consequently,
protein digestion is rarely an issue
in infants. In contrast, fat
digestion and absorption are complex
processes that are strongly
influenced by the development of
pancreatic lipase activity late in
gestation, low intraluminal bile
acid concentrations (in preterm
infants), and possibly limitations
in translocation of fats across the
apical surface of the mucosal cell
and incorporation into chylomicrons.
These factors limit digestion and
absorption of long chain
triglycerides compared with older
children and adults. Despite these
limitations, there is little benefit
to the use of medium chain
triglycerides over long chain
triglycerides under most
circumstances. The gastrointestinal
microbiome (bacteria) can play an
important role in assimilation of
carbohydrates and has implications
for other aspects of preterm health
(for example, necrotizing
enterocolitis). New molecular
methods are providing insight into
the development of the
gastrointestinal microbiome
demonstrating that the neonate’s
gastrointestinal microbiome is quite
different from that of the adult.
Gastrointestinal motility also
affects nutrient assimilation.
Gastric emptying often is less
related to diet than to
developmental factors such as
gestational age. Small intestinal
motility also relates strongly to
developmental age. Gastrointestinal
hormones are now being increasingly
recognized to not only affect
motility (for example, motilin),
gastrointestinal secretion (for
example, secretin), and
gastrointestinal growth (for
example, glucagon-like peptide 2),
but also appetite (for example,
ghrelin), and sensation (for
example, serotonin).
Conclusions: Appropriate feeding of
preterm and term infants can be
based, in part, on our knowledge of
gastrointestinal development.
However, gaps in our understanding
remain as some of our information is
dated. More studies are needed that
follow up on older findings,
evaluate current diets and use
modern methodology.
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