Oat beta-glucan LDL effect linked to molecular weight and gut viscosity

By Jess Halliday

- Last updated on GMT

Related tags: Cholesterol

The ability of oat beta-glucan to lower LDL cholesterol is related to its molecular weight and viscosity in the gut, a new study has found – and manufacture using an extrusion process makes the beta-glucan more soluble and produces higher viscosity.

Beta glucan from oats is renowned for its potential to reduce LDL (bad) cholesterol. The FDA allowing a health clam on reduced risk of heart disease and the European Food Safety Authority (EFSA) recently published a positive generic (article 13.1) health claim on the cause and effect of oat beta-glucan lowering cholesterol.

However the authors of the new study noted that not all the research has drawn positive conclusions. This inconsistency seems to be down to the molecular weight of the beta glucan (MW), which effects viscosity of the gut contents, and its solubility. The higher the viscosity in the upper gut (small intestine) the greater the observed effect on LDL cholesterol.

The researchers said that the MW and solubility can be affected by normal methods of processing and storage. There have been concerns that high temperature and pressure processing would break down the beta-glucan molecules and make them lose their effectiveness. This now seems to be unfounded in the case of extrusion.

The team set out to test whether 3g high MW beta glucan would reduce LDL cholesterol, and whether the cholesterol lowering was related to MW and viscosity.

Their study involved 345 participants with high LDL cholesterol, who were randomly assigned to receive a manufactured extruded cereal with one of four different additions for 4 weeks: wheat fibre; 3g high MW beta glucan; 4g medium MW beta glucan; 3g medium MW beta glucan; or 4g low MW beta glucan. The doses were split across two servings a day.

The study was multi-centre, with participants in Canada, Australia and the United Kingdom. The source of the beta glucan used in the cereals was Oatwell oat bran, supplied by Swiss company CreaNutrition.

Once a week the participants gave a fasting blood sample and were weighed, had their blood pressure measured and changes in medication and any adverse effects were noted. The blood samples were analysed for total and HDL cholesterol, triglycerides, glucose, AST, CRP, urea and creatine, and LDL cholesterol was calculated. The participants also had to provide a diet record.

At the end of the 4 week period, the researchers found that the participants who took the 3g high MW, 4g medium MW, and 3g medium MW beta glucan was significantly lower than those that took the 4g low MW and the wheat fibre – by an average of 0.21, 0.26, and 0.19 mmol/L respectively.

“The physicochemical properties of oat beta-glucan should be considered when assessing the cholesterol-lowering ability of oat-containing products,”​ concluded the researchers. “An extruded breakfast cereal containing 3g oat beta-glucan/d with a high MW (2,210,000 g/mol) or a medium MW (530,000 g/mol) lowered cholesterol similarly by around 0.2mmol/L (5%) but efficacy was reduced by 50% when MW was reduced to 210,000 g/mol.”

Ruedi Duss of CreaNutrition, who was also one of the authors, told NutraIngredients.com that the study is significant because 1.5 g bioactive oat beta-glucan from an eligible oat source consumed twice a day as part of a normal diet has not been studied by any scientific group before.

“As far as we know this is the largest ever published international multicenter RCT trial based on bioactive oat beta-glucan ,”​ he said, drawing attention to the consistent results across three continents.

“And the study could also show non bioactive oat beta-glucan has no effect,”​ he said.

Source: American Journal of Clinical Nutrition
2010, Volume 92, Pages 723-732
"Physicochemical properties of oat beta-glucan influence its ability to reduce serum LDL cholesterol in humans: a randomized clinical trial"
Authors: Wolever, T., Tosh, S., Gibbs, A., Brand-Miller, J., Duncan, A, Hart, V., Lamarche, B., Thomson, B., Duss, R., Wood, P.

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