Dietary fibre guidelines

posted on 02 Aug 2010 13:24 by yattaa in Nutrition

Australian dietary guidelines recommend we eat more breads and cereals (preferably wholegrain) and fruit and vegetables.

Oat bran
The ancient Greeks and Romans celebrated the laxative and satiety value of bran and wholemeal breads.
A century ago, fibre in the diet was thought to be harmful to the body. It was believed to interfere with the absorption of essential nutrients from food and also increase bacteria in the bowel.
New dietary guidelines
Today however, the Australian Dietary Guidelines recommend that we eat more breads and cereals (preferably wholegrain) and fruit and vegetables.
Dietary fibre (or 'roughage') is a complex mixture of different components including the carbohydrates cellulose, hemicellulose, gums, mucilages, pectins and the non-carbohydrate - lignin.
These components are found in cell walls and exudative material secreted by plants.
Fibre chemistry is a recently developed science - the metabolic effects of the isolated and purified fractions of fibre are yet to be adequately defined.

Food sources of dietary fibre
Dietary fibre is found in foods of plant origin only - cereals, vegetables, fruit, dried peas, beans, lentils and nuts.

Wheat bran contains 40-50 per cent fibre, wholemeal bread about 6.5 per cent, brown and most mixed grain breads 4.9 per cent and white bread 2.6 per cent - if not enriched.
Because of their water content, fruits and vegetables are more dilute sources, 1.5-5 per cent. Legumes, nuts and dried fruits are higher in fibre, greater than 7 per cent.
Foods such as meat, fish, eggs, milk and cheese, table sugar and alcohol do not provide dietary fibre.
Foods such as meat, fish, eggs, milk and cheese, table sugar and alcohol do not provide dietary fibre.
About 30-35 grams of fibre should be consumed daily and drink plenty of fluids as this assists the action of fibre.

Fibre in prepared food
Fibre plays an important role in the prevention of a number of diseases.
Fibre should be obtained by eating a variety of different foods.
Second only to Americans, Australians are the most health conscious, and food manufacturers are increasingly improving the production of prepared foods in line with the results of latest research.
Products now available on our supermarket shelves are essentially very high in nutritional value and buyers are also quite well informed on increasing fibre in their diet, eating less salt, less fat and lowering cholesterol.

Oat bran
What is oat bran? Bran is the hard and rather woody protective outer coating of cereal grains which serves to protect the grain before it germinates.

Brans are obtained from the normal milling process of commonly-eaten cereals such as wheat and oats.

What is the difference between wheat bran and oat bran? Wheat and oats are cereals but their grains are rather different. Both contain a germ and a large amount of starch.

The starch provides the energy reserve for the germ as it sprouts to produce a new plant. The starch reserve is called the endosperm which we use for energy when we eat oat porridge, muesli, or the flour from wheat.

Oat grain differs from wheat in that it contains about twice as much polyunsaturated fat. The most noticeable difference is in the outer coat and in the fibre of the grains. Wheat contains a layer of cells called the aleurone which separate the seed coat from the endosperm. During milling, the aleurone and the seed coat are broken apart and very little starch remains.

In oats, the aleurone layer contains much more water-soluble fibre and the cells reach down into the endosperm. During milling the oat bran that separates contains aleurone cells, seed coats and starch.

Do oat bran and wheat bran have different effects? Wheat bran is a very good source of dietary fibre as it is not soluble in water. This gives wheat bran its main beneficial action of being a good (and cheap) laxative - because the fibre increases the mass of the stools.

Wheat bran has few other actions that are considered important.

Oat bran contains some insoluble fibre plus a larger amount of soluble fibre, both of which can help laxation.

The soluble fibre component seems to give the oat bran its other major attraction - that of lowering cholesterol.

How can oat bran lower cholesterol? It has been known for many years that oats and oat products can help to lower blood cholesterol levels in the body. This probably occurs through the increased conversion of cholesterol to bile acids in the liver.

Because oat bran binds bile acids in the intestine, more bile acids are lost when oat bran is eaten, therefore more cholesterol is used to replace the bile acids.

How much oat bran? Raised plasma cholesterol is a major risk factor for early coronary artery disease.

Studies in America have shown that a 1 per cent reduction in cholesterol produces a 2 per cent reduction in the risk.

Feeding experiments in humans have shown that about 60-90 grams of oat bran per day (depending on the type of bran) is required in order to lower blood cholesterol levels appreciably. This amount may provide up to 10 grams of the total fibre intake required per day.

The quantity of rolled oats needed to produce the same effect is larger because oat bran is a more concentrated product.

However, both are pleasant foods which may be eaten with enjoyment.

It is important to realize that one food product in the diet cannot be expected to lower cholesterol levels by itself.

Consumers must also reduce the intake of their total and saturated fats. The value of porridge for breakfast is improved if it replaces more fatty food.