The nutritional literature shows that changes to the levels of certain plasma lipoproteins that carry cholesterol are associated with an increased risk of developing the disease. In particular high plasma levels of the very low density lipoprotein (VLDL; triglycerides), the small dense low density lipoprotein (LDL), and the lipoprotein(a) particle, as well as low plasma levels of the high density lipoprotein (HDL) particle, are associated with an increased risk of cardiovascular disease. The association is interesting because evidence suggests that some other factor is able to cause changes to plasma lipoproteins, and at the same time increase the risk of cardiovascular disease. The metabolic changes associated with syndrome X (metabolic syndrome) have been identified as the probable causative agent. Metabolic syndrome is characterised by non-alcoholic fatty liver, hyperglycaemia, weight gain and hyperlipidaemia. The inflammation associated with the disorder may be a primary driver of cardiovascular disease.
Poor diet is thought to lead to the development of the metabolic changes associated with the metabolic syndrome. Poor diet is therefore likely the causative agent in the association between plasma lipoprotein changes and cardiovascular disease risk. This suggests that high quality diets containing high intakes of unrefined plant foods should be able to favourably affect plasma lipoprotein levels and cardiovascular risk. That fruit and vegetable intakes are beneficial at reducing cardiovascular risk has been well reported in the nutritional literature in epidemiological studies. Further, the beneficial effects of plant foods on plasma lipoproteins has been reported. One study for example1, investigated the effects of dietary vegetable roots (potatoes, parsnips, carrots, beets, rutabagas and turnips), vegetable leaves and stalks (cabbage, broccoli, brussel sprouts, celery, lettuce, onions, cauliflower and spinach), and whole grain (wheat, corn and oats), on the plasma cholesterol of 16 healthy male adults.
Compared to the control diet, grains and leafy vegetables causes significant falls in LDL cholesterol, with grains showing a greater effects. The VLDL fraction of the plasma fell significantly only in the leafy vegetables. Total cholesterol fell significantly in both grains and leafy vegetables, with the latter showing the greatest effect. No changes in HDL or triglycerides were evident following consumption of any of the plant food groups. Taken as a whole these results suggest that plant food favourably affect plasma cholesterol levels, and this is particularly pertinent when considering that the subjects were all healthy young adults, and that the study only lasted 3 months. Had hypercholesterolaemic individuals been used then the results might have been greater. Plant foods can likely favourably affect plasma cholesterol levels because of the fibre they contain. Plant foods are rich source of both insoluble and soluble fibre, but it is the soluble fibre that may be able to influence plasma lipoproteins most favourably.
The western diet is a primary driver of the metabolic syndrome. The changes associated with the metabolic syndrome include detrimental lipoprotein changes and an increased risk of cardiovascular disease. Reversing the metabolic syndrome is as easy as abandoning the Western diet and consuming a traditional diet based on traditional eating practices. Most, but not all traditional diets are rich in plant foods and these are good sources of fibre. Soluble fibre is able to lower plasma cholesterol through a number of mechanisms. Soluble fiber appears to be particularly effective at increasing the excretion of bile acids, which increases cholesterol turnover in the liver. In addition, soluble fibre may be fermented by gut bacteria in the colon and the resulting short chain fatty acids may inhibit cholesterol synthesis. In addition soluble fibre has beneficial glycaemic effects and this may reduce the hyperinsulinaemia and hyperglycaemia associated with the metabolic syndrome.
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