US Pharm. 2006;10:109.

Inulin is a natural food fiber found in more than 30,000 plants, including fruits and vegetables. Inulin resists digestion in the upper gastrointestinal (GI) tract but is fermented by microflora in the colon. This fermentation leads to increased fecal biomass and water content of stools, thereby improving bowel regularity.1 Inulin has also been found to have features different from many other fibers and may have many possible health benefits.2,3

Inulin has a neutral taste and is colorless, texture-free, and highly soluble, allowing it to be added to water, dairy products, or other fluids. Inulin is stable at high temperatures, so it may be added to food prior to cooking or baking or mixed into hot fluids.3 Inulin has been added to several food products, is available in supplement form, and is now available as a fiber supplement in FiberSure.

Inulin, along with other dietary fibers, has been shown to promote regularity. Scientists have postulated that inulin and other fibers have potential health benefits that include improving or maintaining colon health as a prebiotic, lowering cholesterol and glucose, increasing the absorption of minerals, particularly calcium, and improving immune function.1

A review of all studies investigating the potential benefits associated with dietary supplementation using inulin or inulin-type fructo-oligosaccharides in humans has been conducted. Studies were identified using PubMed and GoogleScholar, review articles, and a metasearch engine. Thirty-seven studies were found and are described as follows (studies that looked at more than one result are included more than once):

•   15 studies cover bifidobacterial growth or prebiotic effect4-18;

•   10 studies review the effect on regularity6,7,19-26;

•   four studies cover the effect on mineral absorption27-30;

•   12 studies address potential effect s on lipids, 11 as primary findings and one as a secondary finding10,17,26,31-39;

•   one study addresses immune modulation18; and

•   one study addresses dosing-finding to adverse events.40

Growth of Bifidobacteria/Prebiotic Effect
Prebiotics are nondigestible food ingredients that benefit the host by selectively stimulating the growth or activity of one or a limited number of bacteria in the colon.41 Bifidobacteria is one of the major colonic bacteria studied and is thought to have the most beneficial health-promoting effects.2 Positive effects include protection from enteric infection, lowering of intestinal pH, suppression of putrefactive and pathogenic bacteria, production of vitamins, activation of intestinal function, assistance of digestion and absorption, and stimulation of the immune response.2,42,43

The animal and in vitro evidence supporting inulin's effect on bifidobacteria and its potential as a prebiotic is strong.1 The data are supported by numerous randomized, controlled (albeit small, with less than 20 patients) human trials.4-18 Without exception, these studies showed that dietary supplementation with inulin at a dose of 8 g per day or greater increased bifidobacteria in the range of 7 to 9 log10. The range of the increase was widely variable between individuals. Compared to lower doses, doses higher than 20 g per day were more likely to be associated with complaints of GI problems, primarily flatulence. Only three of the 15 studies included more than 20 patients;5,8,12 this is a limitation.

Effect on Regularity
Ten studies looked at inulin's effect on regularity.6,7,19-26 Nine of these studies showed an increase in either number or weight of stools or decreased enema or laxative use; six had findings that were statistically significant in at least one of the above categories.19-24,27 The one study that showed no difference in whole gut transit time or stool weight involved 21 subjects with irritable bowel syndrome and used low doses of fiber (6 g/day).7 Again, only three of these studies were large (more than 20 patients).7,24,25

Effect on Minerals
Although only four studies have examined the potential for inulin to improve mineral absorption,27-30 two of the studies were large and well designed.28,30 Three of the four studies reported improved calcium absorption after inulin supplementation, even after a period as short as three weeks.27,28,30 The one study that did not find improved calcium absorption was small (N = 12), used a lower dose of short-chained fructo-oligosaccharides (5 g/day), and lasted only three weeks.29 A study conducted in adolescents over the course of one year firmly supported inulin's role in increasing calcium absorption without adversely affecting other mineral content.30

Effect on Lipids and Glucose
Twelve studies looked at inulin's effect on lipids and/or glucose.10,17,28,31-39 Again, most were small; only four studies included more than 20 patients.31,32,35,38 Overall, the findings were mixed. Most of the studies reported no significant effect on lipids or glucose, although the study durations were typically short.

Findings from the largest studies were mixed.31,32,36,38 Furthermore, the studies with the longest durations had inconclusive results.32,37-39 Of note, there was little to no toxicity reported by study subjects, and several studies did report a beneficial effect on lipids and/or glucose.17,35,36,38,39

Effect on Immune Modulation
One small study examined immune modulation, with results supporting inulin's role in improving immune modulation.18 The finding's strength rested in the study population--19 frail elderly patients, in whom improved immune function typically is difficult to stimulate--and in the measures employed (phagocytosis and interleukin-6 mRNA). Its weaknesses were its small study size and the dearth of other studies that replicate or confirm the findings.

Miscellaneous Study
One study was conducted similarly to a dose-finding study for a new drug. It clearly established 40 g as the dose associated with dose-limiting toxicities (i.e., bloating, abdominal cramps, flatulence).40

Overall, the findings on potential benefits of inulin were positive. Inulin clearly increases bifidobacteria and promotes regularity, probably improves calcium absorption, and may improve immune function or the lipid/glucose profile. Of note, the study populations were vastly different and included neonates, adolescents, young adults, and the frail elderly. No group reported problems related to supplementation until doses of 30 to 40 g per day were consumed. It appears that consuming inulin in divided doses of 8 to 10 g per day has the potential to significantly improve health.

--Abigail Brugger

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