Chemistry Reference
In-Depth Information
Although scFOS is not digested, it is fermented in the large intestine, so it con-
tributes some energy to the body via short-chain fatty acids (SCFAs). Acetate is
metabolized in muscle, kidney, heart, and brain; propionate is cleared by the liver,
and is reported to be a glucogenic precursor and suppressor of cholesterol synthesis;
and butyrate is metabolized by the colonic epithelium where it regulates cell growth
and differentiation (Tuohy et al., 2006). Hosoya et al. (1988) measured the caloric
value of scFOS by combining data from two radiochemical balance studies. In the
first study, they adapted subjects to 6.1 g/day of [
14
C] labeled scFOS for 7 days, then
collected breath, flatus, urine, and fecal samples for 48 hours to determine parti-
tioning of the
14
C. In the study, 58 and 67 percent of the
14
C was recovered within
24 and 48 hours, respectively. Most of this was recovered in respiratory gas, with
40 percent recovered within the first 12 hours. Over the 48-hour period, 10 percent
was recovered in feces, 2 percent in urine, and less than 0.05 percent in flatus. The
second study used in the caloric value calculation was an
in vitro
human fecal
incubation study, which measured bacterial SCFA production. Following the 8-hour
incubation, 89 percent of the
14
C was recovered; 10 percent was found in
14
CO
2
,
mostly produced within the first 4 hours, and 58 percent of the
14
C was converted to
SCFA. The primary SCFAs were acetate, propionate, and butyrate, with
14
C present
in the ratios 42:35:20. Combining these two studies, Hosoya et al. (1988) calculated
the caloric value of scFOS to be 1.5 kcal/g, less than half that of sucrose. The pres-
ence of labeled SCFAs and CO
2
indicates that scFOS is utilized by the intestinal
bacteria to generate SCFAs, and that these SCFAs are further metabolized.
2.2.2 bacterial utilization of scFos
As described above, there is direct evidence that bacteria utilize scFOS, dem-
onstrated by the production of labeled SCFAs from labeled scFOS (Hosoya et al.,
1988). However, SCFAs are not accepted as validated biomarkers of prebiotic activ-
ity, that is, selected bacterial growth or activity; hence, well-designed clinical studies
with bacterial enumeration are preferred (Roberfroid, 2005d). Selective utilization
of scFOS by intestinal bacteria has been demonstrated
in vitro
using pure cultures of
selected bacterial species or using mixed fecal flora inoculations, and also in animal
and human studies by measuring the bacterial composition of the feces. This section
describes
in vitro
prebiotic studies and the next section describes clinical prebiotic
evidence.
scFOS is one of only three recognized prebiotics—inulin-type fructans,
trans
-
galacto-oligosaccharides, and lactulose (Gibson et al., 2004). It has been accepted as
a prebiotic because it meets the following three criteria:
1. It resists gastric acidity, hydrolysis by mammalian enzymes, and intestinal
absorption.
2. It is fermented by the intestinal microflora.
3. It selectively stimulates the growth of large intestinal bacteria associated with
health and well-being.
