Barley for Food and Health: Science, Technology, and Products

GLYCEMIC RESPONSE TO CARBOHYDRATE CONSUMPTION 193
The University of Lund researchers subsequently reported some methodology
improvements of the second-meal technique applied to the effect of a low-GI
evening meal on glycemic response to the following morning breakfast meal
(Granfeldt et al. 2006). This study calculated available carbohydrate load as total
carbohydrates minus the indigestible components DF and RS. The evening meals
varied in GI and/or indigestible carbohydrates, and consisted of pasta, barley kernels,
and white wheat bread. Serving sizes were adjusted to correspond with the
DF and RS content. The test evening meals were found to substantially reduce
the GI and insulinemic index of white wheat bread eaten at the subsequent breakfast
meal. Following this study, Nilsson et al. (2007) expanded the study design
to include four different low-GI evening meals and a white bread control. Tests
following the subsequent breakfast meal were expanded to include measurement
of free fatty acid levels, and the markers of colonic fermentation SCFAs in
blood and urine and expired H 2 . The after-breakfast glucose response was significantly
lower following consumption of barley kernels the previous evening than
after white bread or spaghetti with wheat bran. Breath H 2 excretion and plasma
SCFAs were higher at breakfast when subjects had previously consumed barley,
and FFAs were lower, in accordance with earlier reports. These results indicate
that colonic fermentation of the specific indigestible carbohydrates present as
well as low-GI features may both influence the improved glucose tolerance at
breakfast. A follow-up study (Nilsson et al. 2007) was conducted to elucidate the
mechanism of improved glucose tolerance at breakfast. Test evening meals consisted
of high-GI white bread (WWB), WWB + barley + barley DF corresponding
to the DF of barley kernels, low-GI spaghetti + barley DF, spaghetti + double
amounts of barley DF (2*DF), spaghetti + oat DF, or whole-grain barley flour
porridge. The rationale of the treatment containing spaghetti + double the barley
DF (2*DF) was to mimic the DF content of the whole barley kernels in the earlier
studies. At breakfast the morning after the test meals, blood glucose, insulin,
SCFAs, FFAs and breath H 2 were measured. The most effective evening meal
for lowering glucose response was spaghetti + 2*DF. This meal also resulted in
the highest breath H 2 excretion. The glucose incremental AUC after breakfast
was correlated positively with fasting FFAs, suggesting colonic fermentation as
a modulator of glucose tolerance through a mechanism leading to suppressed
FFA levels. This study demonstrated that the low GI of a food per se is not
attributable to slow digestion and absorption of sufficient magnitude to induce
overnight benefits. These researchers suggested the possibility that the presence
of abundant fermentable fiber in a food may be a more reliable indicator of
potential low glycemic responses. More recently (Nilsson et al. 2008), this group
repeated the study using both boiled barley kernels and WWB + barley fiber + RS
at an evening meal. At breakfast, glucose response was negatively correlated with
colonic fermentation and GLP-1 and positively correlated with fasting FFA. The
levels of the pro-inflammatory marker IL-6 were lower at breakfast, and fasting
adiponectin was higher after the previous barley kernel evening meals. These
results support their hypothesis of high fermentable fiber as the definitive factor
in physiological responses in carbohydrate metabolism.