Not all types of carbohydrate can be digested and broken down into glucose. Indigestible carbohydrate is called fibre. In recent years some kinds of starches, not previously classified as fibre, have been found to be resistant to digestion. They are called ‘resistant starches’ we spoke about in the last email.
Fibre is a natural constituent of a healthy diet high in fruits, vegetables, lentils, beans and wholegrains. If you eat such a diet you have less risk of bowel cancer, diabetes or diverticular disease, and are unlikely to suffer from constipation. Contrary to the popular image of fibre as mere ‘roughage’, it can actually absorb water. As it does so, it makes faecal matter bulkier, less dense and easier to pass along the digestive tract. This decreases the amount of time food waste spends inside the body and reduces the risk of infection or cell changes due to carcinogens that are produced when some foods, particularly meat, degrade. Bulkier faecal matter also means less chance of a blockage, or constipation.
There are many different kinds of fibre, some of which are proteins, not carbohydrates. Some fibre, such as that found in oats, is called ‘soluble fibre’ and combines with sugar molecules to slow down the absorption of carbohydrates. This type therefore helps to keep blood sugar levels balanced.
Some fibre is much more water-absorbent than other types. While wheat fibre, for example, swells to ten times its original volume in water, glucomannan fibre (from the Japanese konjac plant) swells to 100 times its volume in water. Highly absorbent types of fibre, by bulking up foods and slowing down the release of sugars, can help to control appetite and play a part in weight maintenance.
Watch this Film The Truth About Fibre to see how much water different forms of fibre absorb.
The average daily intake of fibre in the UK and US is around 20g, which is less than half that of rural Africans who consume around 55g a day and suffer from few of the lower digestive diseases so common in the West. An ideal intake of fibre is not less than 35g a day. For example, if you have a cup of oats, an apple and a heaped tablespoon of seeds for breakfast this will provide 15g of fibre.
A large salad containing crunchy vegetables, such as carrots, cabbage or broccoli pieces, may give you a further 15g. A meal based on beans, lentils or peas is likely to provide a further 15g.
Provided the right foods are eaten, 35g can easily be achieved without the need to add extra fibre. Professor of Nutrition, John Dickerson, from the University of Surrey, has stressed the danger of adding wheat bran to a nutrient poor diet. The reason for this is that wheat bran contains high levels of phytate, which reduces the absorption of essential minerals, including zinc. Overall, it is probably best to get a mixture of fibre from oats, lentils, beans, seeds, fruits and raw or lightly cooked vegetables. Much of the fibre in vegetables is destroyed by cooking, so vegetables are best eaten crunchy.
One way to get soluble fibres is to have a tablespoon of chia seeds a day. Another is to eat whole oat products. You can further up your soluble fibre intake by adding a teaspoon of oat bran to cereal. Soluble are also in vegetables, although somewhat destroyed by heat and hence prolonged coking. They behave quite differently to, for example, wheat fibre.
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