Tocotrienols, soluble dietary fibre and blood cholesterol

Author

Ross Lhood

Proceeding

6th Asian Congress Of Nutrition: Nutritional Challanged & Frontiers Towards Year 2000, Kuala Lumpur, Malaysia.

Date

16/9/1991

Keyword

tocotrienols, hypocholesterolaemic properties, soluble dietary fibre, ß-glucans, blood cholesterol

Abstract

Introduction: Elevated blood cholesterol concentration, in particular, the concentration of low-density lipoprotein cholesterol, has been shown to be a major risk factor in the development of atherosclerosis and cardiovascular diseases. Elevated blood cholesterol is linked to increased risk of cardiovascular disease (1-3) and proponents of cholesterol reduction claim a fall in serum cholesterol of 1% is associated with at least a 2% fall in coronary heart disease (4). Blood cholesterol concentration can be reduced by controlling the composition and quantity of dietary fat and by including food components (e.g. soluble dietary fibre, tocotrienols) that possess hypocholesterolaemic properties. The only forms of dietary fibre with the ability to lower blood cholesterol are the water-soluble fractions. Guar gum (5), pectins (6), xanthan gum (7) and locust bean (8) have been shown to be effective in lowering blood cholesterol in animal experiments and human trials. Oat bran also lowers plasma cholesterol (9) and this appears to be due to a high concentration of soluble β-glucans (10,11). The hypocholesterolaemic effect of soluble dietary fibres is due to either/or a combination of two or more possible mechanisms.  Firstly, soluble fibre may increase the viscosity of the digesta, increasing the thickness of the unstirred layer hence reducing the uptake of cholesterol and bile acids (12). Secondly, soluble dietary fibre is an excellent substrate for microbial fermentation in the caecum and large intestine and the resultant volatile fatty acids may suppress hepatic cholesterol synthesis (13). Thirdly, the presence of soluble fibre may cause tropic effects on the enzymes and the structure of the gastrointestinal tract (14,15). Tocotrienols, unsaturated analogues of tocopherols, are not widely found in nature, however, palm oil and its fractions, and barley contain high concentrations of tocotrienols. Palm oil is especially rich in a-tocotrienol (16). Recently, Qureshi et al (17) isolated tocotrienols from barley flour and showed that they inhibited the activity of 3-hydroxy-3-methylglu-taryl coenzyme A reductase in chickens. A number of human trials (18-20) have since shown that capsulated vitamin E concentrate from palm oil (Palmvitee), which is rich in tocotrienols, is effective in reducing blood cholesterol.