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Title: Site, rate and extent of starch digestion in weaning infants
Author: Christian, Martin Tremayne
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2003
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Background: The colon is believed to salvage energy from unabsorbed starch especially when the capacity of the small intestine to digest it is limited. The extent to which this occurs is not known. Aims: The aim of this thesis was to determine site and relative extent of starch digestion and fermentation in young children using the individual and combined approaches of stable isotope breath tests and in vitro stool fermentation models. Stable Isotope Breath Test Methods: Thirteen children (10m, 3f), median (range) age 11.8 mo (7.6 -22.7 mo), took a starchy breakfast containing 13C labelled wheat flour following an overnight fast. Duplicate breath samples were obtained before breakfast and every 30 min for 12 h. Breath 13CO2 enrichment was measured by isotope ratio mass spectrometry and results were expressed as percentage dose recovered (PDR) for each 30 min. PDR data were analysed and mathematically curve fitted either assuming a constant estimate of CO2 production rate or adjusted for physical activity. Stable Isotope Breath Test Results: Mean ± SD cumulative 13C PDR (cPDR) at 12 h was 21.3% ± 8.4% for unadjusted data and 26.5% ± 11.6% for adjusted data. A composite fit of two curves fitted significantly better than a single curve. Curve fitting allowed estimation of cPDRs of small intestine (17.5% ± 6.5% and 22.7% ± 9.3% for unadjusted and adjusted data respectively) and colon (4.6% ± 2.9% and 6.3% ± 5.4 %). From these results it is speculated that the colon may account for up to 20% of starch digestion in young children. In Vitro Colonic Fermentation Methods: A simulated colonic environment was used to account for the fate of raw and cooked starch that was fermented in the colon of young children. A slurry was prepared from faecal samples of 6 infants (7-10 mo), 6 toddlers (16-21 mo) and 7 adults (24-56 years). Each slurry was anaerobically incubated with raw or cooked maize starch in MacCartney bottles in a shaking water bath. Parallel incubations were stopped at 4 and 24 h. The headspace gas volume was analysed for CO2 and methane. The culture supernatant was analyzed for the volatile short chain fatty acids acetate, propionate and butyrate (SCFA), lactate and residual starch. In Vitro Colonic Fermentation Results: There was a decreasing trend of SCFA production with age at 4 h which was not evident at 24 h. At 4 h, toddler stools produced the most CO2 followed by infants and then adults, but this trend was not seen at 24 h. Methane was detected in 3 adults only. Lactate was detected mainly at 4 h in children only. The production of SCFA at 4 h generally declined with age but the differences at 24 h were less marked, suggesting fermentation is a more rapid process in young children than in adults. A highly efficient energy salvage process may take place in the colon of young children. Calculations Using Both Data Sets and Conclusions: Using data from studies described in both parts of the dissertation, it has been possible to derive stoichiometric equations for the whole gut digestion of starch, and thereby calculate its potential energy. There are a number of limitations to the methodology and from assumptions that have been made, but this provides an attractive means to calculate relative roles of small intestine and colon to starch digestion in young children which in turn may form the scientific basis for nutritional advice given to mothers.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available