High-Fiber Diet Helps Fight Disease

High-Fiber Diet Helps Fight Disease

A high-fibre diet is good for you. Everyone knows that. But in recent years the proliferation of claim and counterclaim about insoluble fibre, soluble fibre, oat bran versus wheat bran and fresh fruit versus wholemeal bread has made what once seemed a simple prescription for health a bit of a muddle. No longer is it clear just what the word “fibre” means.

For instance, most people think that fibre cannot be digested. It is true that fibre, the structural bit of a plant, cannot be broken down by ordinary digestive juices in the stomach and the small intestine. But it can be broken down, at least in part, in the large intestine, by the millions of bacteria which colonize that part of our bodies. Much of the bulk of feces is actually made up of the dead bodies of these bacteria.

Fibre is not a single entity. There are several kinds of fibre in food, and they each have different effects on the body during their passage through the digestive tract.

Insoluble fibre is cellulose. It is sometimes called crude fibre and it makes up only a small percentage of the total fibre in an average diet. The soluble fibres, such as the gums in oats and dried beans, and pectin, are completely digested by the bacteria in the large intestine, leaving acids in their wake which stimulate the wall of the intestine to contract.

One kind of dietary fibre, lignin, undergoes almost no digestion, but there is evidence that it helps the body get rid of cholesterol by stripping away bile acids (one of the major functions of cholesterol in the body is to make these acids).

A diet high in fibre is handy in treating and preventing constipation. The acids produced during the digestion of fibre stimulate and speed the movement of food through the body, and the fibre itself absorbs water, giving bulk to feces.

There is also evidence that fibre can help prevent hemorrhoids, hernias of the intestinal wall, colon cancer and possibly cardiovascular disease.

It is believed that by speeding up the passage of food through the body, fibre might help eliminate toxic nasties before they have a chance to cause disease, but there is also some evidence that the acids produced during the digestion of fibre could act as anti-cancer agents.

The picture is clouded somewhat by the fact that a high-fibre diet is also usually fairly low in fat. Since a high consumption of fat is known to increase a person’s risk of cancer, it is unclear how much of the benefit in a high-fibre low-fat diet is due to the fibre and how much to the low level of fats.

There is some evidence that a high-fibre diet, in conjunction with low intakes of fat and sugar, can help diabetics control their disease. The fibre found in some foods, such as oats and legumes, forms a gel on the surface of the stomach which helps slow the rate at which sugar enters the bloodstream.

Most people consume about 15g of dietary fibre a day. Nutritionists recommend that 30 to 40g would be a better target.

But there are dangers in eating too much fibre. Fibre absorbs iron and zinc as it passes through the digestive system, potentially robbing the body of these essential nutrients. Bran by itself will not cure constipation. It needs water to make it swell and do its job and, in fact, if bran is eaten without adequate fluid to complete the cure, constipation can actually worsen. Large amounts of unprocessed bran can cause the cells lining the intestine to be damaged.

Anyone planning to embark on a diet higher in fibre should do so gradually. A sudden shift to a high fibre diet can cause the digestive system to revolt, resulting in wind, nausea and even vomiting.

Ideally, dietary fibre should be obtained from a variety of sources. Foods which are very high in fibre include baked beans (13g of fibre to a cup of beans), pumpernickel bread (5.6g a slice, compared with 2g for a slice of wholemeal bread), dried dates and figs, split peas, pumpkin and raspberries. Foods with surprisingly little fibre include cherries (0.4g in 10 cherries) and grapes (0.3g for the same number).

Flour is relatively high in fibre, which means that most white bread contains about 0.8g of fibre a slice (about the same as a tablespoon of sultanas). That is not great, but it means that white bread is not really the dietary baddie it is sometimes made out to be.

Variety is the key when it comes to fibre. It is much more pleasant to get your daily requirement from a selection of unpeeled fresh fruit and vegetables, along with some whole grain bread, than it is to grind your way through a few tablespoons of unprocessed bran at breakfast time. Look at it this way: a tablespoon of wheat bran has 2.2g of fibre. An unpeeled apple has 2.5g. Which would you rather eat?



Natalia, a health researcher and passionate blogger who enjoys learning, discovering, and sharing tips on Lifestyle & Wellness.

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One Comment

  1. Ben says:

    Thanks for explaining what fiber is and how it can help if we get enough of it in our diet. I appreciate that you said that fiber can’t do the job all on its own. It needs plenty of water too. People see isolated pieces of information, like they need more fiber, and run with that without considering the other things that your body needs to get the best out of that extra fiber.

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