The Effects of Prebiotic Fiber Inulin on Satiety and Gastrointestinal Tolerance and Prebiotic Properties of a Yeast Fermentate In Vitro

Abstract

The prevalence of chronic non-communicable diseases continues to rise in the United States. Cardiovascular disease (CVD), type 2 diabetes, obesity, hypertension, and associated inflammatory conditions threaten the health and wellbeing of the population. One dietary strategy to combat this trend is the promotion of dietary fiber intake. Dietary fiber offers numerous health benefits with consumption including the reduced risk of certain cancers and CVD, maintenance of healthy blood glucose levels, promotion of healthy bodyweight through enhanced satiety, and promotion of healthy blood lipid profiles. Prebiotics are a subcategory of fiber which offer all mentioned health benefits in addition to selective stimulation of beneficial gut bacteria, immuno-protective properties, attenuation of inflammatory pathways, and promotion of epithelial barrier integrity. Inulin is an extensively studied prebiotic fiber and is most often seen as an isolated powder derived from chicory roots. Inulin is also found abundantly in Jerusalem artichokes, and to a lesser extent in onions, bananas, garlic, leeks, and wheat. Jerusalem artichokes offer a whole food fiber source which can be incorporated into meals or blended into beverages. However, little work has been done evaluating the gastrointestinal tolerance (GIT) and satiety properties of Jerusalem artichokes. Given a recent consumer interest of incorporating more healthful whole foods into the diet, Jerusalem artichokes serve as an available, affordable, whole food vegetable offering a rich source of prebiotic fiber and health benefits upon consumption. The objective of our first study was to compare two forms of inulin, an isolated powder and a whole food source (Jerusalem artichokes), and to identify their effects on satiety and GIT when blended into a breakfast smoothie. We hypothesized that Jerusalem artichokes would promote greater satiety and be better tolerated when compared to inulin powder. In a randomized, single-blind, crossover designed study, 26 participants (13 females, 13 males) fasted for 12 hours and then consumed a chocolate breakfast smoothie with inulin powder or Jerusalem artichoke puree mixed in. A plain smoothie without fiber was used as a control. The primary outcome was to observe satiety using a visual analog scale (VAS) to assess hunger, satiety, fullness, and then assess prospective food intake. The secondary outcome was to observe GIT through surveys probing the presence and severity of common adverse gastrointestinal symptoms. Satiety was generally not different based on treatment group within four hours of smoothie consumption, with one exception at the 60-minute timepoint where those consuming Jerusalem artichokes indicated greater feelings of fullness than those receiving the inulin powder or control smoothie (P = 0.016). No significant differences in GIT were observed other than a slight increase in reported flatulence for both treatment groups when compared to a control at the 30-minute timepoint (P = 0.042). These data indicate that neither treatment promoted greater satiety than a control, and that both sources of inulin were well tolerated without producing adverse gastrointestinal symptoms in healthy adults. As efforts to identify new prebiotics continue, the objective of our second study was to measure prebiotic properties of a yeast fermentate in an in vitro system. Yeast (Saccharomyces cerevisiae) is used widely in human and animal nutrition for the contribution of micronutrients, antioxidants, amino acids, and other bioactive compounds. The fiber content of yeast fermentates has been shown to have prebiotic effects and the ability to alter the gut microbiota in a positive direction for gut health in several animal species, although data with human subjects is lacking. We hypothesized that a yeast fermentate would selectively stimulate the growth of Bifidobacteria and Lactobacillus, while also increasing short chain fatty acid (SCFA) production in an in vitro simulated human microbiome environment. In our trial, human fecal samples were used with practical doses of a yeast fermentate, 0.5 g/L and 1.5 g/L, to compare SCFA, lactate, Bifidobacteria, Lactobacillus, ammonium (NH4+) and branched SCFA production. Maltodextrin was a placebo treatment. The yeast fermentate demonstrated prebiotic properties by beneficially altering microbiome activity and increasing Lactobacillus, butyrate, and propionate in a dose-dependent manner with the strongest effects being observed for the highest test dose (P < 0.05). This research supports that a yeast fermentate has prebiotic activity. Further, the changes we observed in gut microbiota and levels of SCFAs may be the mechanism by which yeast fermentate improves immune response and gut health seen in animal species. The results from these two studies provide valuable data towards the continued evaluation of prebiotic compounds. Even though we did not see an effect on satiety from the two inulin sources tested, we found that Jerusalem artichokes were well tolerated and easy to blend into a beverage. With the current interest of incorporating healthy whole foods into the diet, this information will be valuable to consumers and provide a new option for achieving greater fiber intake. Our yeast fermentate data provide evidence of prebiotic properties in vitro using human fecal donors, which indicates a likelihood of prebiotic health benefits for humans upon consumption that are currently demonstrated in animal species. And while there are currently a limited number of supporting studies to officially classify yeast fermentates as prebiotics for humans, these data strengthen that argument.