<p>Obesity and nutrition-related
non-communicable diseases continue to be major challenges that are increasing
in severity worldwide. Science-centered carbohydrate dietary strategies may be
a viable approach to help address such challenges. Recent reports from our
laboratory indicate that certain carbohydrates with slow digestion profiles
have the ability to trigger the gut-brain axis and reduce food intake and to
slow gastric emptying and potentially affect appetite. Slow carbohydrate
digestion may have other impacts on energy metabolism that have not been
explored. In the current investigations, we sought to better understand the
delayed gastric emptying profile of pearl millet-based foods as well as to
understand how altering carbohydrate digestion rate impacts substrate utilization
for energy.</p>
<p>In the first study, the
physical breakdown of pearl millet couscous particles in a simulated gastric
environment (Human Gastric Simulator) was studied compared to wheat couscous
matched in particle size, and select physicochemical properties of each type of
couscous were characterized. Because we previously showed that pearl millet
couscous had a marked delay in gastric emptying compared to white rice, boiled
potatoes, and pasta in a human study in Mali, the objective of the first investigation
was to test the hypothesis that pearl millet couscous was more resistant to
breakdown in the stomach than wheat couscous and would take longer to empty.
Our findings indicated that pearl millet couscous instead broke down into
smaller, more numerous particles than wheat couscous. However, pearl millet had
a slower starch hydrolysis property compared to wheat couscous per unit surface
area. Pearl millet also had a smaller amylose chain length (839-963 DP) compared
to wheat (1225-1563 DP), which may enable a denser packing of millet starch
molecules that hinders hydrolysis. We also visually observed that the pearl
millet particles formed a paste while breaking down that could reasonably
generate viscosity in the stomach to potentially delay gastric emptying. </p>
<p>Based off the findings
from simulated gastric digestion, we next conducted a human study (<i>n</i>=14)
in the U.S. to test the hypothesis that pearl millet-based foods (couscous –
commercial and self-made, thick porridge) would reduce glycemic response, increase
satiety, and delay gastric emptying compared to wheat couscous and white rice.
We complemented this human study with additional <i>in vitro </i>work using an
advanced gastrointestinal digestion system (TIMagc) to determine if the
viscosity of pearl millet couscous particles as they were breaking down in the
stomach was contributing to a decrease in gastric emptying. Our findings indicated
that all the pearl millet-based foods and wheat couscous had lower overall
glycemic response than white rice, but only the self-made millet couscous
showed higher satiety through subjective appetitive response ratings.
Surprisingly, there were no differences in gastric emptying among the foods.
Additionally, the half-emptying times for these foods were all ~3 h, which is similar
to the comparably low half-emptying times observed for white rice, boiled
potatoes, and pasta in the previous Mali study. We now hypothesize that there
may be diet-induced changes in gut-brain axis signaling when slowly digestible
carbohydrates are consumed repeatedly over time, perhaps through modulating the
number or sensitivity of small intestinal L-cells. We also found that millet
couscous did not exhibit high viscosity in the TIMagc, suggesting that
viscosity was not impacting its rate of gastric emptying. We conclude that at
least some pearl millet-based foods possess a slow digestion property that may
act to trigger the gut-brain axis or ileal brake to increase feelings of
satiety or slow gastric emptying, but the discrepancy between U.S. and Malian
populations requires further study. </p>
<p>In the final
investigation, we examined how altering carbohydrate digestion affected partitioning
of carbohydrate versus fat for oxidation as well as the efficiency of switching
oxidation between these two substrates (termed “metabolic flexibility”) in
mice. Metabolic flexibility has been associated with good health related to
decreased adipose tissue in the body and improved insulin sensitivity and may
have implications on weight management. Carbohydrate digestion was adjusted by:
(1) testing mice that lacked a complete set of enzymes by knocking out
maltase-glucoamylase (Mgam; null) for moderating starch digestion versus
testing wild-type mice; (2) using diets in these two groups of mice to moderate
starch digestion that had different levels of resistant starch (53%, 35%, and
18%), had only raw corn starch or sucrose, or were high in fat; and (3)
providing a supplement of fungal amyloglucosidase (AMG) to the mice treatment
groups to increase starch digestion. Respiratory exchange ratio (RER) was
measured through indirect calorimetry and mathematical modeling was used to
characterize the diurnal shifts in RER (sine equation) as well as carbohydrate
versus fat oxidation and metabolic flexibility (percent relative cumulative
frequency [PRCF] with Weibull and Mixed Weibull Cumulative Distribution
functions). Our results suggest that null mice lacking Mgam had somewhat
increased metabolic flexibility than wild-type mice despite exhibiting minimal
to no effects on carbohydrate oxidation. Intriguingly, the raw corn starch diet
increased fat oxidation and generally promoted metabolic flexibility, although
it did not increase carbohydrate oxidation relative to the other
carbohydrate-predominant diets. Increasing carbohydrate digestion through AMG
supplementation increased carbohydrate oxidation, and generally prompted
earlier shifts to carbohydrate oxidation than without AMG supplementation.
These findings provide a basis for better understanding the metabolic
consequences of altering carbohydrate digestion and establish novel tools that
can be utilized in future investigations. Overall, we propose that moderating
carbohydrate digestion provides the ideal combination of balancing carbohydrate
and fat oxidation while promoting metabolic flexibility. </p>
<p>In conclusion, a slow
digestion property may enable some types of pearl millet to trigger the ileal
brake and gut-brain axis feedback systems to decrease glycemic response and increase
satiety. Moreover, consuming carbohydrates with slow digestion may optimize
substrate utilization for energy by the body. In addition to triggering the
ileal brake and gut-brain axis, modulating carbohydrate digestion to more
effectively switch between carbohydrate and fat for oxidation may be beneficial
for weight management and metabolic disease prevention.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14046713 |
| Date | 01 March 2021 |
| Creators | Anna MR Hayes (8477520) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/In_vitro_and_in_vivo_investigations_of_carbohydrates_with_different_digestibilities_for_improved_satiety_and_metabolic_health/14046713 |
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