Legumes are a source of all three recognised forms of dietary fibre – soluble fibre, insoluble fibre and resistant starch – which are responsible for many of the protective effects of legumes.

Insoluble fibre – This type of fibre provides bulk and promotes regularity.  In one study that analysed the insoluble dietary fibre (i.e. lignin, cellulose and hemicellulose) content of raw lentil, kidney beans and chickpea samples, the insoluble fibre values were found to be 24.9%, 21.6% and 17.4% respectively.

Soluble fibre – The soluble fibre content of legumes has been shown to decrease LDL-cholesterol. Water-soluble fibres lower the reabsorption of bile acids, which in turn, increases the hepatic conversion of cholesterol into bile acids. This ultimately leads to increased LDL-cholesterol uptake by the liver. It is estimated that for each additional gram of water-soluble fibre in the diet, serum total and LDL-cholesterol concentrations decrease by -0.028 mmol/L and -0.029 mmol/L, respectively.

Resistant starch – These are starches that ‘resist’ or escape digestion in the small intestine.  Resistant starches have been defined as “the sum of starch and products of starch digestion not absorbed in the small intestine of healthy individuals.” These starches reach the large intestine, where they are fermented by resident bacteria, producing a variety of end products, including short chain fatty acids (SCFA), particularly butyrate. Butyrate is the favoured energy source of colon cells and it has been shown to have anti-carcinogenic properties. Most notably, published research has shown butyrate reverses neoplastic changes in vitro and it induces apoptosis (programmed cell death) of human colorectal cancer cells. Lentils and baked beans are the best known sources of resistant starch (sub-type RS1) within the legume food ranks.

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