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<title>Resistant Starch For Health
<S/F>Many nutritionists think that resistant starch should be classified as a component
of dietary fibre. By Dr Antigone Kouris.
<text>Historically starch has been thought to be 100 percent digested to glucose in the
small intestine. Research over the last few decades has found that a significant portion
(about 10 percent) is not digested in the small intestine and passes into the large
intestine where it is a substrate for bacterial fermentation.
The bacteria in the large intestine produce short chain fatty acids from the resistant
starch which may help maintain the health of cells lining the colon (colonocytes) and
prevent bowel cancer.
These fatty acids are also absorbed into the bloodstream and may play a role in
lowering blood cholesterol levels. A new study suggests that resistant starch may also
help with weight loss.
A study by Higgins et al, published in October 2004 issue of Nutrition and Metabolism
showed that replacing 5.4 percent of the carbohydrate content of a meal with resistant
starch increased fat oxidation by 23 percent in a sample of 12 study subjects.
This increase is apparently sustained throughout the day, even if only ONE meal
contains resistant starch and the increased fat oxidation is sustained if one keeps eating
RS on a daily basis.
It appears that the resistant starch changes the order in which the body burns food.
Usually carbohydrates are used first, but when resistant starch is present, dietary fat is
oxidised first into energy before it has a chance to be stored as body fat. This study
suggests that including foods high in resistant starch in THE daily diet may help with
weight management.
STARCHY FACTS
Starch is made up of glucose molecules linked together to form amylose and
amylopectin. Amylose has a linear molecular structure and can stack to form tightly
packed granules which is insoluble and hard to digest whereas amylopectin has a
branched structure and thus cannot form tightly packed granules and is thus easier to
digest.
Most plants contain about 20 to 25 percent amylose. However, other plant sources like
pea starch have 60 percent amylose and certain species of maize starch have 80
percent amylose (eg Hi-Maize). These plants are therefore very high in resistant starch.
The physical and chemical composition of starch determines whether starch is digested
in the small intestine or whether it ferments in the colon. There are several reasons why
starch may not be digested:
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Some starch may be physically trapped inside intact plant cells as in wholegrain
foods like muesli and grainy bread. This starch is therefore inaccessible because
digestive amylases are unable to penetrate or break down the cellulose cell
walls.
The higher the amylose content of starch, the greater its resistance to digestion
because they form tighly packed granules in cells. Raw potato, green bananas,
pulses and high amylose maize starch have a high amylose content.
When starch is heated, starch granules swell and are disrupted. This process,
known as gelatinisation, makes the starch much more accessible to digestive
enzymes.
Starch with a high amylose content and starch which is inaccessible due to the
physical structure in which it is located, are less susceptible to gelatinisation.
They are hence are more resistant to digestion.
When starch that has been heated and cooled, retrogradation occurs and
converts some of the gelatinised starch to a crystalline form, which is resistant to
digestion.
Foods, such as bread, cornflakes, cold cooked potato, rice and pasta contain
retrograded starch that is resistant to digestion.
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HOW MUCH IS GOOD?
Some resistant starch is measured when total dietary fibre is measured. There is
currently no official analytical method for measuring the resistant content of foods.
It has been estimated that resistant starch intake in Australia is around five to seven
grams per person per day. Approximately, 20 grams a day is recommended to obtain
the beneficial health benefits of resistant starch.
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SOURCES OF RESISTANT STARCH
Resistant starch can be found in every day foods such as the following:
 Intact wholegrain cereals/seeds/nuts (unprocessed) such as oats, rye, wheat,
barley, semolina, corn, linseed and sesame.
 Processed starchy foods such as some breakfast cereals (like cornflakes), white
bread, rice and pasta.
 Processed starchy foods with added RS called Hi-Maize derived from corn such
as some breads and cereals.
 Legumes such as lentils and baked beans (legumes have the highest content of
RS).
 Unripe fruit, especially banana.
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Cooking and cooling the food can also increase the resistant starch content such
as cooked cold rice (eg sushi rice), cold pasta salad and cold boiled potato salad.
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Note: Article courtesy of www.healthyeatingclub.org.
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