A diet abundant in whole-grain cereals, vegetables and
fruits has health promoting effects, which the nutritionists believe to be due
to many factors, such as phytochemicals or fiber-polyphenolic complexes,
working together. On the other hand, a Western-type diet includes foods such as
French fries, processed red meats, high-fat dairy products and refined grains
and sweets that contain high amounts of saturated fat, cholesterol and protein
or easily absorbable carbohydrates. This dietary pattern leads to lifestyle
diseases such as type-2 diabetes, cardiovascular disease (CVD), cancers or even
A Western-type diet, of course, does no good to the
gut health because of lack or limited dietary fiber. So, dietary supplements
are used to increase the dietary fiber in such type of diets.
Inulin is a natural fiber found in numerous fruits and
vegetables. Although it is not digested in the upper gastrointestinal tract, it
is easily fermented by the gut bacteria in the colon. This fermentation leads
to fecal biomass and water content of stools, thus improving bowel movements.
Studies have shown that inulin has a prebiotic
effect as they stimulate the growth of bifidobacteria in colon thereby
protecting the colon from infection, lowering the intestinal pH (lower pH is
beneficial for gut health), assisting in digestion and absorption and also
stimulating the immune response.
Grapefruit contains a type of anti-oxidant called flavonoid
which has shown benefits like improving mineral metabolism and bone health,
lowering blood cholesterol.
Earlier research by the investigators of this study
indicated that supplementation of standard
diet with grapefruit flavonoids increased the intestinal pH and also
decreased the activity of certain microbial enzymes (which is not good).
However, adding inulin to the flavonoid decreased the pH in the hindgut,
increased the microbial activity and normalized the water content of digested
So, this time, the researchers, Adam Jurgonski and
colleagues from the Institute of Animal Reproduction and Food Research, Polish
Academy of Sciences, Poland, examined whether grapefruit flavonoid extract and
inulin combo in a Western-type diet
may provide synergistic effects to hindgut metabolism, as well as blood lipid
and mineral profiles.
Forty male Wistar rats were distributed into 4 groups and
fed for 28 days with diets rich in fat, cholesterol and protein. The control
diet (C) contained 5 percent of sucrose. The inulin diet (IN) had 5 percent of
The results showed that -
• The IN diet showed beneficial changes within the
hindgut such as i) lowered the pH in the hindgut ii) increased bifidobacteria
growth and iii) increased production of propionate and butyrate.
• The 0.3 percent grapefruit flavonoid extract (GFE) diet
caused a considerable enlargement of the hindgut tissue and digestion. The
hindgut microorganisms were not able to sufficiently metabolize the flavonoid
glycosides of GFE.
• An increased and a non-constipated stool output was
observed with GFE feeding.
• The GFE diet group showed a decreased concentration of
ammonia, iso-butyric acid, valeric acid and iso-valeric acid. The decreased
ammonia concentration is considered a positive change because this compound can
destroy cells, alter nucleic acid synthesis, induce cancerous cell growth and
increase viral infections at concentrations in the lower bowel of usual Western
diets, according to the researchers.
• Dietary IN beneficially suppressed the increased
digested mass observed after GFE feeding.
• IN + GFE diet
slightly decreased the pH value and increased the bifidobacteria number and the
propionate concentration, however to the level observed with the control
• The serum cholesterol concentration was similar among
all dietary groups; however, the serum
triglyceride concentration decreased significantly in the GFE group regardless
of the dietary carbohydrate type.
The researchers concluded that 'Inulin does not provide any additional benefit to the blood lipid
profile caused by dietary application of the grapefruit flavonoid extract and
it does not counteract clearly detrimental effects of the extract in the
They also cautioned that adding grapefruit extract to the
diet could cause possible adverse hindgut responses with overdoses.
Jurgonski A, Juskiewicz J, Kowalska K, Zdunczyk
Z. Does dietary inulin affect biological activity of a grapefruit
flavonoid-rich extract? Nutr Metab (Lond). 2012 Apr 11;9(1):31.