They say the discovery could lead to ways of boosting the cholesterol-fighting properties of other cereals including wheat.
University of Queensland professor Mike Gidley said the study, funded through the Australian Research Council Centre of Excellence in Plant Cell Walls, revealed new information on the function of beta glucans.
The findings challenged the theory that beta glucans 'mop up' bile, which is secreted during digestion, and prevent its absorption in the small intestine.
In a study using pigs as a model for humans, researchers found that the beta glucan in oats actually reduced, rather than maintained, the total amount of circulating bile.
Writing in the FASEB Journal, they stated: “Although oat beta glucan (BG) has been shown to decrease blood cholesterol in intervention trials, the detailed mechanism is not yet defined, but restricted reabsorption of bile acids (BAs) has been hypothesized.
“Using pigs as a model for humans we demonstrated that, compared to the control, BG added to the diet for 26 days caused decreases of 24% in blood total BAs, 34% in total cholesterol and 57% in LDL cholesterol.”
It adds there was “a 50% reduction in BA active transport across ex vivo ileum after 40 minutes. The results suggest that BG not only physically hinders the active reabsorption of BAs and uptake of cholesterol, but also changes the BAs profile with lower circulating levels without excess excretion in the faeces, thus resulting in reduced blood TC and LDL-C.”
Lead researcher Dr Purnima Gunness said it was previously thought that the body's use of cholesterol to make new bile was one of the mechanisms for how beta glucans reduced the amount of cholesterol in the blood stream.
Dr Guinness added they were not yet sure why, but the study clearly showed that in the presence of beta glucan, there is actually much less circulating bile.
"This means that fats, which bile helps break down, are not digested as rapidly or as completely.
"Now that we know how the beta glucans positively impact on cholesterol levels, it will help us identify other fibres in plant cell walls that may have a similar effect," Dr Guinness said.
Source: FASEB Journal
"Reduction in circulating bile acid and restricted diffusion across the intestinal epithelium are associated with a decrease in blood cholesterol in the presence of oat β-glucan".
Authors: Purnima Gunness, et al.