Barley β-glucan increases fecal bile acid excretion and short chain fatty acid levels in mildly hypercholesterolemic individuals
Thandapilly, S.J., Ndou, S.P., Wang, Y., Nyachoti, C.M., Ames, N.P. (2018). Barley β-glucan increases fecal bile acid excretion and short chain fatty acid levels in mildly hypercholesterolemic individuals. Food and Function, [online] 9(6), 3092-3096. http://dx.doi.org/10.1039/c8fo00157j
Plain language summary
The cholesterol lowering effect of beta-glucan, a type of soluble fibre found in barley and oat, has been well established and approved by various food regulatory agencies around the globe. Despite the many studies showing the benefit of consuming beta-glucan on the management of high cholesterol levels, researchers still did not know the underlying mechanism responsible for its positive effect in the body. Therefore, the objective of the present study was to determine the physiological mechanism of cholesterol lowering by examining the effects of dietary beta-glucan on compounds that are known to facilitate digestion and absorption of lipids in the small intestine as well as regulate cholesterol levels in the body, namely bile acids. Towards this objective, a human feeding trial was conducted where participants with higher blood cholesterol levels consumed barley foods containing either high viscosity beta-glucan or low viscosity beta-glucan at different concentrations. Fecal samples from the participants were analyzed for the amount of bile acids excreted and short chain fatty acids (end products of fermentation of dietary fibers by the gut microbiota). Results from this study showed for the first time that increased bile acid elimination through the feces is one of the primary mechanisms by which beta-glucan lowers blood cholesterol in humans. Furthermore, this study showed that the level of fementability of the fibre is varied based on its characteristics, which was evident from significantly increased levels of short chain fatty acids produced in response to the high viscosity beta-glucan. Overall the present study provides new insights into the mechanisms behind the cholesterol lowering effect of cereal derived beta-glucan and advances the science around the health benefits of barley.
The cholesterol-lowering effect of barley β-glucan has been proposed to be the result of a pleiotropic effect, which involves several biological mechanisms such as gut fermentation, inhibition of intestinal cholesterol absorption and increased bile acid excretion and its synthesis. However, one of the recent studies from our laboratory indicated that increased bile acid excretion and subsequent increase in its synthesis, but not the inhibition of cholesterol absorption or synthesis might be responsible for the cholesterol-lowering effect of barley β-glucan. Accordingly, the primary objective of the present study was to investigate the concentration of bile acids (BA), neutral sterols (NS) and short chain fatty acids (SCFA) excreted through the feces by mildly hypercholesterolemic subjects who consumed diets containing barley β-glucan with varying molecular weights (MW) and concentrations. In a controlled, four phase, crossover trial, 30 mildly hypercholesterolemic but otherwise healthy subjects were randomly assigned to receive breakfast containing 3 g high MW (HMW), 5 g low MW (LMW), 3 g LMW barley β-glucan or a control diet for 5 weeks. The concentrations of BA, NS and SCFA in the feces were measured at the end of each treatment phase. Compared to the other treatment groups, 3 g day-1 HMW barley β-glucan consumption resulted in increased lithocholic acid (LCA) excretion (P < 0.001) but not LMW β-glucan, even at the high dose of 5 g day-1. Increased fermentability of fibre was also evident from a significant increase in fecal total SCFA concentrations in response to the 3 g HMW β-glucan diet compared to the 3 g LMW barley β-glucan and control diet (P = 0.0015). In summary, the current results validate our previous report on the role of fecal bile acid excretion in cholesterol lowering through the consumption of barley β-glucan. In addition, increased SCFA concentrations indicate that an increase in β-glucan molecular weight promotes hindgut fermentation, which might also be playing a role in attenuating cholesterol levels.