Direct and indirect effects of dietary fibre on plasma lipoproteins in man

Abstract

In clinical practice two effects of dietary fibre should be distinguished: A direct, and an indirect effect. An indirect effect of dietary-fibre-rich foods is that they displace from the diet foods high in saturated fat and cholesterol. Thus legumes may displace meat, and whole-wheat bread may displace cookies and cakes. As a result, diets high in fibre-rich foods tend to cause low levels of plasma low-density-lipoprotein (LDL) cholesterol. Direct effects of fibre are those seen in strictly controlled experiments where intake of all other nutrients is forcibly held constant. Under those conditions we and others observed the following effects:

- Wheat bran fibre does not cause a fall of plasma cholesterol, but may even induce a slight rise.

- Pectin, both isolated or as a constituent of vegetables and fruits, can lower cholesterol by up to 10%.

- The fibre of soy beans present in soy protein concentrate does not have a favourable effect on plasma lipoproteins.

- Addition of fibre-rich foods such as pulses, oats, fruits and vegetables to a conventional lipid-lowering diet caused an extra fall of 10% in plasma cholesterol on top of the 20% fall already caused by the reduction of saturated fats and cholesterol and the increased intake of polyunsaturated fatty acids. The decrease in high-density lipoprotein (HDL) cholesterol caused by the lipid-lowering diet was partly reversed by the addition of plant foods.

- Extreme high-carbohydrate fat-restricted diets cause a fall in HDL as well as in LDL, and the decrease in HDL cannot be completely prevented by the presence of fibre in the diet.

In conclusion, fibre-rich foods have direct and indirect effects that are of benefit in the prevention and treatment of acquired hypercholesterolaemia.