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.
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
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
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.