Bread and Fibre

Bread and Fibre

Sourced from the Consumer Information Division

Bread Research Institute of Australia

PO Box 7, North Ryde NSW 2113

What is Dietary Fibre?

Dietary fibre is a very complex mixture of different components which give the rigid structure to plant cell walls.  Sometimes referred to as roughage, it is generally regarded as not absorbed by the human digestive tract.  However, recent research shows that many of dietary fibre’s components are broken down to sugars, gases (carbon dioxide, methane and hydrogen) and volatile fatty acids (acetate, propionate and butyrate) by bacterial fermentation in the large bowel.

Which foods contain Dietary Fibre?

Dietary fibre is found only in foods derived from plants, such as cereals, bread, vegetables, fruit, legumes and nuts.  It is not found in animal foods, sugar or alcohol.

In Australia 37% of our dietary fibre comes from cereal sources, 33% from vegetables, 20% from fruit, and 10% from other food sources.

How much fibre should I be eating?

Health authorities recommend that Australians should increase their dietary fibre intake from the present level of about 20 g, to closer to 30 g per day.  Bread can make a valuable contribution to achieving this goal.  Women should eat at least 4 – 5 slices of bread per day.  If this amount is eaten as Wholemeal or fibre-increased bread it will provide approximately 10 g of dietary fibre, or 33% of the recommended intake.  Seven to eight slices of bread is suggested for men, which will provide around 15 g of dietary fibre (about 50% of the suggested intake).

Crude Fibre v Dietary Fibre

The Australian Food Standards Code requires that the declaration of fibre content on food labels must be in terms of dietary fibre.

However, for classifying breads into categories e.g. wholemeal, fibre increased etc. the requirements is crude fibre.

Crude fibre measures part of the insoluble dietary fibre and none of the soluble dietary fibre.  Hence it significantly underestimates total dietary fibre (by as much as 80%).

BREAD FIBRE STANDARDS

(NH & MRC 1991)

Type of Bread Crude Fibre % (dry Basis)
Brown 1.0 minimum
Fibre increased 1.85 minimum
Wholemeal 1.8 minimum
Wholemeal fibre increased 2.7 minimum

DIETARY FIBRE CONTENT OF SELECTED FOODS

>6 mg/100g

Dark Rye

Wholemeal Fibre-increased Bread

Wholemeal Bread

Bran breakfast cereals

Dried Fruit

Almonds, peanuts

4-6 mg/100g

White fibre-increased Bread

Mixed Grain Bread

Brown Bread

Berry Fruit

Spinach

Peas

Dried beans and peas

2-4 mg/100 g

White bread

Apples

Oranges

Carrots

Potatoes

Sweetcorn

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*Figures in brackets represent average serving size

Dietary fibre figures from Composition of Foods Australia (1989) Dept of Community Services and health.  All figures rounded off.

What are Fibre-increased Breads?

Fibre-increased breads are now available on the market in response to consumer recognition of the importance of fibre.  The fibre may be derived from any edible cereal (oats, maize, rye, legumes (peas, beans) or tuber (potato, cassava).

These breads must comply with Australian Food Regulations for the minimum quantity of fibre they contain.  White, high-fibre breads contain the same amount of crude fibre as wholemeal bread.  Wholemeal fibre-increased breads contain half as much again.  Many mixed grain breads are ow being labelled as fibre-increased.  Their fibre content is equivalent to wholemeal breads.

How much Fibre is there in Bread?

All breads are a source of dietary fibre, with wholemeal bread being the best.  Contrary to popular opinion, white bread contains dietary fibre-about one third that of wholemeal.  White flour, the main ingredient in white bread, contains about 70 – 80% of the whole wheat grain.  This includes a significant proportion of the bran layers.  The cell wall material found in the endosperm also contributes fibre to white flour.

Brown breads and mixed grain breads have a fibre content falling between wholemeal and white.Australian Food Standards stipulate minimum Fibre contents for wholemeal and brown breads.

Why is Fibre Important?

Fibre is important, not for its nutritive properties, but for how it affects our body functions.

Although originally thought to be a single substance, research has now shown that fibre is actually a mixture of various components which have different actions.

  • Insoluble fibres e.g. cereal fibres, are important in regulating bowel function.  The act by absorbing water and softening the stools.
  • Soluble fibre e.g. pectin and gums (found in fruits, vegetables and rolled oats) and saponins (in legumes) can help lower cholesterol.

Fibre delays the rate at which food leaves the stomach, resulting in a feeling of “fullness” – a benefit in weight control.

Increasing the amount of fibre in the diet will usually result in a lower intake of high fat and high sugar foods.

Most high fibre foods provide valuable vitamins and minerals.

Should we obtain fibre from food or from special fibre supplements?

Health authorities recommended that fibre be obtained from food rather than supplements.  Although supplements e.g. unprocessed bran, may be beneficial in the short term, they do not contribute the important nutrients of fibre-rich foods.  In addition the effects of fibre may been enhanced by the other components in food.  Excessive use of unprocessed bran i.e. more than 1 – 2 tablespoons daily, is not recommended as it may adversely affect levels of other nutrients in the diet.

Are there any dangers in eating too much fibre?

Studies indicate that fibre may affect the absorption of minerals, particularly iron, calcium, magnesium and zinc.  Phytates, found in wholegrain cereals, may render these nutrients unavailable.  Fibre may also affect the digestibility of fat and protein, and inhibit the absorption of certain drugs.  However, much of the evidence to date is conflicting.  If one is consuming a nutritionally adequate diet, these adverse effects should not pose a problem.