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By Ivan Nikolov
copyright © 2008 Ivan Nikolov
In this article I will make an attempt to present what is
available as knowledge about resistant starch – a topic that is still little
Scientists have been studying resistant starch for over 20 years now but there
is still need for more precise methods of research to bring a lot more
knowledge that will clarify some very important points in relation to the
effects of resistant starch on the human body and especially those in relation
to proper sports nutrition.
The topics that I’ll touch on are those, most closely related to the nutrition
part in the sports of bodybuilding such as: physiological effects of resistant
starch; lipid metabolism; resistant starch and insulin and glucose response, GI
and GL. But let’s first take a quick overview to help us get an idea what a
resistant starch is and where it comes from:
Resistant starch (RS) has recently been defined as “… the sum of starch and
products of starch degradation not absorbed in the small intestine of healthy
individuals”. In other words RS is that portion of starch (roughly about 15 per
cent) that is not readily digested and thus surpasses the small intestine. To
date several categories of RS are identified:
RS1 - Physically inaccessible starch due to the presence of intact cell walls
in grains, seeds or tubers. Mainly found in partly milled grains, seeds and
RS2 – This is the group of the raw ungelatinized (uncooked) starches. They are
classified in 3 main types: A (ex. most cereal starches, cassava starch), B
(ex. Green banana and raw potato starches) and C (most legume starches). RS2 is
called high-amylose maize starch.
RS3 – Retrograded starch is a starch that has been cooked and then cooled and
stored for periods of time, ranging from several hours to several months
(cooked and cooled potatoes, bread, cornflakes, food products with prolonged
and/or repeated moist heat treatment).
RS4 – Chemically modified starches. These are derived due to cross bonding with
chemical reagents, ethers, esters, etc. (certain modified breads, pastas and
The first three groups (RS1, RS2 and RS3) can actually
coexist in starchy foods. For ex. RS1 and RS2 are both present in bananas, and
RS1 and RS3 can be found in beans.
The American Association of Cereal Chemists and the Food
Nutrition Board of the Institute of Medicine of the National Academies
currently defines RS as a type of dietary fiber.
How was it found?
Englyst and coworkers accidentally found RS in 1982 while
performing in vitro experiments. They found that after enzymatic hydrolysis
some starch remained not hydrolyzed.
Consequent in vivo studies showed that RS resist digestion
in the stomach and the small intestine and are then delivered in the large
intestine where RS act as a substrate for microbial fermentation. The end
products of this process are short chain fatty acids (SCFA), hydrogen, carbon
dioxide and methane.
Structure and energy value
The two main components of starch are amylose and
amylopectin. As a general rule starches that contain more amylose (the linear
fraction of starch) produce more RS after retrogradation than those with mainly
amylopectin content (the crystalline fraction of starch).
In other words starches rich in amylose are generally more
resistant to digestion and also more susceptible to retrogradation.
Retrogradation occurs when starch is heated in water above its gelatinization
temperature and then cooled. When cooked beyond certain temperature starch
granules gelatinize (melt) thus becoming more readily digestible.
However, these starch gels are unstable and upon cooling
re-form crystals that are resistant to hydrolysis by amylases (digestive
enzymes). Reheating of starch reduces the RS content while continuous cycles of
reheating and cooling have shown to increase RS.
Studies suggest that the energy value of RS is
approximately 2 kcal/g (8 kJ/g) as opposed to the energy value for completely
digestible starch 4.2 kcal/g (15 kJ/g) (Liversey 1994).
Physiological effects of RS
As already mentioned above RS escape digestion in the upper intestinal tract
and once in the large intestine they are subject to fermentation by the
microflora with end-products SCFA (short chain fatty acids), hydrogen, carbon
dioxide and methane.
As being of most importance to the human health we will
now focus our attention mainly on SCFA. SCFA are a product of bacterial
fermentation. The main components are butyrate, propionate and acetate with the
first one being produced in significantly higher levels in comparison with the
SCFA are the main energy source of the colonocytes (the
colon mucosa). They help lower the pH of the intestine, increase colonic blood
flow, help reduce the presence of toxic ammonia, and help prevent the
development of abnormal colonic cell populations. SCFA are known as a
bio-marker for colonic health.
It’s worth mentioning also that RS serve as a physical
protection for the probiotics. These are cultures of live microorganisms, which
are shown to regulate the flora in the intestinal tract. Therefore, resistant
starch is prebiotic, based on its probiotic protecting and stimulating
RS and lipid metabolism
RS were continuously shown to cause a significant
reduction in a number of measures of lipid metabolism (total lipids, total
cholesterol, LDL, HDL, VLDL, triglycerides, triglyceride-rich lipoproteins) in
Studies with humans have shown controversial results.
J. A. Higgins and co. performed a study on12 subjects who were given meals
containing 0%, 2.7%, 5.4%, and 10.7% RS as a percentage of total carbohydrate
The conclusion of their study: “The data indicate that
replacement of 5.4% of total dietary carbohydrate with RS significantly
increased post-prandial lipid oxidation and therefore could decrease fat
accumulation in the long-term.
However, some other studies indicate that RS consumption does not affect the
measures of lipid metabolism in humans (Nugent, A. P). Therefore it is evident
that more research is needed to help us better understand the effects of RS on
lipid metabolism in humans.
RS and insulin and glucose metabolism, GL and GI
Insulin is a hormone directly responsible for the
transportation of the blood glucose from the blood stream to the muscle and
adipose (fat) cells.
Avoiding insulin spikes is considered the main factor in
body weight management as this hormone not only stores the blood glucose in the
adipose cells but also inhibits the release of fat and its subsequent use for
Foods rich in RS cause slow and steady insulin release, which enables for a
greater percentage of the stored fat to be transported to the liver and
eventually used for energy. Therefore, RS play a very important role in the
insulin response moderation, this way regulating the glucose metabolism.
As a consequence RS-rich foods are important aid in the
body weight management, treatment of obesity, decreasing the risk of developing
diabetes as well as other major diseases.
In a recent study Y. Yamada and co. examined the inhibitory effect of a single
ingestion of bread containing 6 g of resistant starch (test food) on the
postprandial blood glucose levels in male and female adults.
Bread not containing resistant starch (placebo) was used
as control food. They concluded: “…Postprandial increases in both blood glucose
and blood insulin were significantly inhibited in subjects in the borderline
group who took the test food in comparison with the placebo group.
Although consumption of foods, rich in RS generally
results in reduced glycemic response it isn’t still clear whether this is due
to the lack of digestible carbohydrates or RS poses specific physiological
properties resulting in decreased glycemic response.
However, due to the same low glycemic response, RS display
an interesting and beneficial relation to the glycemic index (GI- an index that
ranks foods oh how they affect the blood glucose level) and glycemic load (GL-
it measures how much of carbohydrate is in a serving with a certain GI).
If some of the digestible carbohydrates are replaced with
RS that will help lower the overall GL this way decrease the negative effect on
health that some carbohydrate foods with high GI and GL might have.
How much RS is required for good health?
Currently an official analytical method for measuring the
resistant content of foods doesn’t exist. It has been estimated that resistant
starch intake in Australia is around 5-7 grams/person/day; 3 – 6 in EU; 10 – 18
in India and China and 2.76 in the UK.
Approximately 20 grams a day is recommended to obtain the beneficial health
benefits of resistant starch.
Natural and commercial sources of RS
A short list of natural sources of RS includes cereal starches, green banana,
raw potato, cooked and cooled potato, legume starches and other food products
with repeated moist heat treatment.
In addition to the natural food sources of RS, some commercially manufactured
forms of RS such as Hi-maize, a commercial form of RS2, and NOVELOSE 330, a
form of RS3 are also available.
As mentioned by A. P. Nugent in his extensive report on RS “there are number of
advantages to using commercially manufactured sources of RS in food products.
Unlike natural sources of RS (e.g. legumes, potatoes, bananas), commercially
manufactured resistant starches are not affected by processing and storage
For example, he states, the amount of RS2 in green bananas
decreases with increasing ripeness, however, a commercial form of RS2,
Hi-maize, does not experience these difficulties.
Although more long term research on humans is needed, it
is clear that RS posses many health benefits with the greatest and most well
researched one being the protective benefit that RS has on the colon.
It is of a big importance also the fact that RS have shown
to have prebiotic (probiotic promotion and protection) functions thus helping
for the regulation of the intestinal flora.
However, in relation to bodybuilding applied nutrition,
more long-term studies are needed to determine to what extend RS may be
eventually beneficial for better management of the lipid and glucose
ABOUT THE AUTOR
Ivan Nikolov, an accomplished natural bodybuilder shares a
wealth of information on Natural
Bodybuilding and Sports
Nutrition on his website www.IvanNikolov.com.
Start using his comprehensive Free Nutrition
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