The Ins and Outs of Inulin, a Food with Function
High in fiber, inulin is a collective term for a large group of complex carbohydrates found in nature. Tasteless and odorless, inulin blends easily with fiber compounds and other nutrients. It has been popping up frequently as a component of nutritional supplements that claim to be weight loss aids. Because of its high physiologic utility, inulin is considered a "functional food" and is on the US Food and Drug Administration's list of Generally Recognized as Safe products.1
Inulin is composed of large numbers of fructose molecules—up to several thousand strung end to end.2 A soluble dietary fiber, inulin is found in more than 36,000 plant species around the world,3,4 but most inulin is extracted from the chicory root. It has no color and no odor and has little taste.
Inulin exerts substantial prebiotic actions. It has been shown to stimulate growth of the Bifidobacterium species and Lactobacillus species both in vitro and in vivo, likely as a result of the low-level fermentation that occurs in the gut.5,6 Because of this action and its fiber component, inulin is beneficial for the maintenance of gut microflora, for maintenance of blood glucose and lipid homeostasis, and for immunomodulation.5 In addition, inulin has become the gold standard for measuring glomerular filtration rate because of its ability to resist enzyme degradation and reabsorption in the renal tubules.7
Inulin has shown promise in weight reduction as a strategy for those with prediabetes. Researchers randomly assigned 44 subjects to either inulin or plain cellulose supplementation8 and monitored them for weight loss as well as intrahepatocellular and intramyocellular fat and glucose levels. Although both groups lost nearly the same amount of weight by week 9, subjects taking inulin continued to lose weight throughout the following 9 weeks. The percentage of body fat reduced was nearly 3 times greater in the inulin group than in the cellulose group at the end of 18 weeks, and intrahepatocellular lipid levels in the inulin group were reduced nearly 5 times the rate found in the cellulose group.8
In another report, the influence of prebiotics and inulin on bowel movements was studied.9 A group of 38 women who underwent intra-abdominal radiation following surgery for gynecologic cancer was randomly assigned to receive either placebo (maltodextrin) or a prebiotic with inulin and fructo-oligosaccharide.9 Patients reported the number of bowel movements per day, the consistency of the bowel movements, and a self-rating of the quality-of-life indicators of insomnia and diarrhea. At the end of the study, which lasted from before beginning radiation therapy to 3 weeks after the last treatment, patients on the prebiotic formulation reported significantly improved scores regarding the number of days of watery stool, compared with the placebo group. The highest scores for quality of life measures were for insomnia and diarrhea in the placebo group but only for insomnia in the treatment group.