Elevated plasma levels of very low density lipoprotein (VLDL) and the small dense sub-fraction of low density lipoprotein (LDL) are associated with an increased risk of cardiovascular disease. Dietary legumes from the Fabinaceae family of plants have been extensively investigated for their ability to lower elevated levels of these lipids. To date, research has identified a number of mechanisms by which legumes may lower elevated levels of LDL and VLDL. In particular, the soluble fibre content has been suggested to be beneficial because it may decrease the glycaemic effect of food. This delayed absorption of glucose may in term favourably lower the plasma insulin to glucagon ratio, with subsequent increases in the oxidation of fatty acids and improvements in insulin sensitivity. However, various lines of reasoning suggest that the fibre content is only one reason for the ability of legumes to lower plasma lipid levels.
For example, researchers1 have investigated the effects of 30 days of broad bean consumption (Vicia faba) in men aged between 18 to 20 years. The subjects had been diagnosed with borderline high (total cholesterol 5.2 to 6.2 mmol/L, LDL cholesterol 3.4 to 4.1 mmol/L) or high (total cholesterol >6.2 mmol/L and LDL >4.1 mmol/L) plasma lipid levels. Of the men with borderline high plasma lipids, one half received ground cooked bean flour, whereas the other half received ground wheat flour, supplemented into their diets. Of the men with high plasma lipids, one half received cooked bean flour, while the other half received raw bean flour, supplemented into their diets. The results showed that after 30 days, bean consumption had significantly lowered plasma glucose, insulin, total cholesterol, VLDL and LDL. Significant increases in plasma glucagon and high density lipoprotein (HDL) were also reported.
These result suggest that broad beans are effective at causing significant reductions in plasma lipid levels. The observation that plasma insulin levels fell, whereas plasma glucagon levels rose, suggests that the effect may have been due to a favourable change in the plasma insulin to glucagon ratio. This data supports other studies that show a reduction in the glycaemic effects of food following bean consumption. Soluble fibre may create a gel-like barrier in the unstirred layer adjacent to the enterocytes, which interferes with the absorption of glucose. However, the largest reductions in plasma lipid levels were seen in subjects consuming raw bean flour, suggesting that the lipid lowering effects may have been partly due to some temperature labile element within beans. In addition, the fibre content of the bean flour amounted to only 2 g/d, suggesting that the lipid lowering effect were caused partly by some non-fibre related component.
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