Effect of the Molecular Weight of Oat β-glucan on Its Ability to Lower Serum Cholesterol

Effect of Varying Dose and Molecular Weight on the Serum LDL-cholesterol-lowering Properties of Oat β-glucan

The purposes of this study were:

1. To determine if a breakfast cereal containing 3g of high molecular weight oat beta-glucan fiber would lower low-density lipoprotein (LDL) - cholesterol (the "bad" cholesterol) compared to a control cereal containing wheat fiber.
2. To determine if the LDL-cholesterol-lowering effect of oat beta-glucan fiber was reduced when the molecular weight of the fiber was reduced.

The FDA allows a health claim that oat products may reduce the risk of heart disease, based on meta-analyses showing a cholesterol-lowering effect of oat beta-glucan, if the product delivers at least a 3g daily dose of oat beta-glucan. However, not all studies have demonstrated a lowering of oat products. This may be due to variable bioactivity of the beta-glucan in the oat products. The bioactivity of oat beta-glucan is believed to depend upon its viscosity in the gut. Factors influencing viscosity include the molecular weight (MW) of the beta-glucan molecule and the amount of soluble beta-glucan in the product, which, in turn determines its concentration (C) in solution. In finished food products both MW and C can be modified by beta-glucanase enzymes present in other ingredients in the food (eg. wheat flour), processing (eg. extrusion) and storage (eg. freezing of moist products such as muffins). The effect of altering the MW and solubility of beta-glucan in foods on glycemic responses has been shown, but a role for MW and C in cholesterol lowering has not been established.

To address this issue, this study was designed with 2 primary objectives:

1. An extruded oat cereal containing 3g high-molecular weight oat β-glucan daily will reduce LDL cholesterol compared to a control wheat bran cereal.
2. A significant correlation exists between LDL cholesterol and log(C×MW), where C is the amount of soluble β-glucan in the daily dose of cereal and MW is the molecular weight of the β-glucan in the cereal.

Inclusion Criteria:

• body mass index 18.5 to 40.0 kg/m^2
• no intention to lose or gain weight
• fasting total cholesterol 5.0 to 8.0 mmol/L
• fasting LDL cholesterol 3.0 to 5.0 mmol/L
• consuming diet containing <15% energy from saturated fat

Exclusion Criteria:

• use of any cholesterol-lowering drug, herbal or nutritional supplement
• regular consumption of oatmeal, oat bran or psyllium - containing cereals
• fasting serum triglycerides >4.0mmol/L
• serum aspartate transaminase >1.5 times upper limit of normal
• serum urea or creatinine >1.8 times upper limit of normal
• presence of diabetes or fasting glucose >6.9mmol/L
• presence or recent major surgical or medical event
• allergy to wheat or oats
• presence of condition or drug which alters digestion or absorption of foods