Plant-based foods (fruits, vegetables, whole-grain, beans, legumes) contain fibre and most contain soluble and insoluble fibre. Both types have specific health benefits: soluble fibre is contained inside plant cells and absorbs water, forming a gel-like substance that slows down the process of digestion. It also slows down the absorption of glucose and reduces absorption of LDL (unhealthy) cholesterol. Insoluble fibre is found in the cell walls of plants. Although it absorbs water, it cannot be dissolved. Acting like a natural laxative by adding bulk, insoluble fibre aids the passage of stools through the intestines, useful in the prevention of constipation and diverticulosis.
Soluble fibre: beans and lentils, oats, pulses, fruit and vegetables
Insoluble fibre: wholegrain bread and cereals, brown rice, fruit and vegetables
“Soluble fibre dissolves in water, forming a gel, and is fermented in the colon by bacteria to a greater extent than insoluble fibre. Short-chain fatty acids and gas are the active metabolites of soluble fibre, both of which decrease the gut transit time. In contrast, insoluble fibre undergoes minimal change in the digestive tract and shortens colonic transit, causing an increase in the faecal mass.”
Bijkerk C et al (2004), Aliment Pharmacol Ther, 19: 245–251