Resistant starch is starch and starch degradation products that escape from
digestion in the small intestine of healthy individuals. Resistant starch
occurs naturally in foods but is also added to foods by the addition of
isolated or manufactured types of resistant starch.
Some types of resistant starch are fermented by the large intestinal
microbiota, conferring benefits to human health through the production of
short-chain fatty acids, increased bacterial mass, and promotion of
butyrate-producing bacteria. Resistant starch functions as a mild
laxative and consuming it can lead to flatulence at high doses.
Origin and history The concept of resistant starch arose
from research in the 1970s and is currently considered to be one of three
starch types: rapidly digested starch, slowly digested starch and resistant
starch, each of which may affect levels of blood glucose.
The Commission of the European Communities has supported research
eventually leading to a definition of resistant starch.
Health effects Internal fermentation of resistant
starch can cause gas when high quantities are consumed. One review
estimated that the acceptable daily intake of resistant starch may be as
high as 45 grams in adults, an amount exceeding the total recommended intake
for dietary fiber of 25-38 grams per day. Resistant starch may contribute to
colon health by increasing regularity, reducing pH, and producing short-chain
fatty acids, among which butyrate is a primary energy source for colonic cells.
In its various forms, resistant starch is digested and/or fermented variably,
leading to preliminary research of resistant starch subtypes on disease
risk. For example, although effects on weight management have been implicated,
there is no evidence that resistant starch has an effect on human weight or
energy balance, and it is not known if resistant starch has any part to play in
helping treat obesity-related disease. When isolated resistant starch is used
to substitute for flour in foods, the glycemic response of that food is
reduced. There is preliminary evidence that resistant starch, used as a
substitute for refined carbohydrate, may increase insulin sensitivity and may
reduce the risk of type 2 diabetes. RS2 resistant starch from high amylose
corn helps to treat diarrhea when delivered in oral rehydration solutions
to people with cholera, rotavirus and other diarrheal diseases.
Starch structure Plants produce starch with different
types of structure and shape characteristics which may affect
digestion. For instance, smaller starch granules are more available to enzyme
digestion because the larger percentage of surface area increases the enzyme
binding rate. Starch consists of amylose and
amylopectin which affect the textural properties of manufactured foods.
Starches with high amylose content generally have increase resistant
starch. Definition and categorization
Resistant starch is any starch or starch digestion products that are not digested
and absorbed in the stomach or small intestine and pass on to the large
intestine. RS has been categorized into four types:
RS1 Physically inaccessible or undigestible resistant starch, such as
that found in seeds or legumes and unprocessed whole grains.
RS2 Resistant starch is inaccessible to enzymes due to starch conformation, as
in high amylose corn starch RS3 Resistant starch that is formed when
starch-containing foods are cooked and cooled, such as pasta. Occurs due to
retrogradation, which refers to the collective processes of dissolved starch
becoming less soluble after being heated and dissolved in water and then cooled.
RS4 Starches that have been chemically modified to resist digestion
Processing effects Processing may affect the natural
resistant starch content of foods. In general, processes that break down
structural barriers to digestion reduce resistant starch content, with greater
reductions resulting from processing. Whole grain wheat may contain as high as
14% resistant starch, while milled wheat flour may contain only 2%. Resistant
starch content of cooked rice may decrease due to grinding or cooking.
Other types of processing increase resistant starch content. If cooking
includes excess water, the starch is gelatinized and becomes more digestible.
However, if these starch gels are then cooled, they can form starch crystals
resistant to digestive enzymes, such as those occurring in cooked and cooled
cereals or potatoes. Cooling a boiled potato overnight increases the amount of
resistant starch. Nutritional information
Resistant starch is considered both a dietary fiber and a functional fiber,
depending on whether it is naturally in foods or added. Although the U.S.
Institute of Medicine has defined total fiber as equal to functional fiber plus
dietary fiber, U.S. food labeling does not distinguish between them.
The Institute of Medicine Panel on the Definition of Dietary Fiber proposed two
definitions: functional fiber as "isolated, nondigestible carbohydrates
that have beneficial physiological effects in humans", and dietary fiber as
"nondigestible carbohydrates and lignin that are intrinsic and intact in
plants." They also proposed that the prior classifications of soluble versus
insoluble be phased out and replaced with viscous versus fermentable for each
specific fiber. Uses
= Resistant starch in food= Starch has been consumed by people and
animals for thousands of years. Thus, foods containing resistant starch are
already commonly consumed. It has been estimated that average
resistant starch intake in developed countries ranges from 3-6 grams/day for
Northern Europeans, Australians and Americans., 8.5 grams/day for Italians
and 10-15 grams/day in Indian and Chinese diets. The higher consumption of
starch-containing foods like pasta and rice likely accounts for higher intake
of resistant starch in Italy, India and China.
Several studies have found that the traditional African diet is high in
resistant starch. Rural black South Africans consume an average of 38 grams
of resistant starch per day by having cooked and cooled corn porridge and
beans in their diets. = Isolated resistant starch=
Isolated and extracted resistant starch and foods rich in resistant starch have
been used to fortify foods to increase their dietary fiber content. Typically,
food fortification utilizes RS2 resistant starch from high amylose corn,
RS3 resistant starch from cassava and RS4 resistant starch from wheat and
potato, as these sources can survive varying degrees of food processing
without losing their resistant starch content.
Resistant starch has a small particle size, white appearance, bland flavor and
low water-holding capacity. Resistant starch typically replaces flour in foods
such as bread and other baked goods, pasta, cereal and batters because it can
produce foods with similar color and texture of the original food. It has
also been used for its textural properties in imitation cheese.
Some types of resistant starch are used as dietary supplements in the United
States. RS2 from potato starch and green banana starch maintain their resistance
as long as they are consumed raw and unheated. If they are heated or baked,
these types of starch become rapidly digestible. RS2 resistant starch from
high amylose corn can be consumed raw or baked into foods.
Physiological effects By definition, resistant starch does not
release glucose within the small intestine, but rather reaches the large
intestine, where it is consumed or fermented by colonic bacteria.
On a daily basis, human intestinal microbiota encounters more carbohydrates
than any other dietary component. This includes resistant starch, non-starch
polysaccharide fibers, oligosaccharides and simple sugars which have
significance to colon health. The fermentation of resistant starch
produces short-chain fatty acids, including acetate, propionate and
butyrate and increased bacterial cell mass. The short-chain fatty acids are
produced in the large intestine where they are rapidly absorbed from the
colon, then are metabolized in colonic epithelial cells, liver or other
tissues. The fermentation of resistant starch produces more butyrate than other
types of dietary fibers. Modest amounts of gases such as carbon
dioxide, methane, and hydrogen are also produced in intestinal fermentation,
with one review estimating that daily intake of resistant starch can be as
high as 45 grams/day in adults before gas production becomes problematic.
References