Resistant Starch (RS):Any health benefit?
Starches refer to long chains of glucose that are found in grains, tubers, legumes and various food products. They form a greater percentage of the Ghanaian diet. Some of these starches may not be easily digestible. Sometimes a small part of it passes through the digestive tract unchanged and undigested.
Starch that specifically resists digestion in the digestive tract is termed resistant starch (RS). This means the starch passes through the stomach and the small intestines undigested by the enzymes, and then finally reaches the large intestines where it is then acted upon by the bacteria there. Resistant starch is considered as a type of dietary fibre available in nature. Dietary fibre refers to all the components of plant food that pass through the stomach and small intestines undigested. Dietary fibre includes soluble fibre, insoluble fibre and RS.
Resistant starch functions like soluble or fermentable fibre that travels through the digestive tract, eventually rea
Types of RS
Type 1: This is contained in grains, seeds and legumes and impedes digestion because it is bound within the fibrous cell walls.
Type 2: This can be found in foods, including raw potatoes and unripe bananas.
Type 3: Formed when some foods such as potatoes and rice are cooked and then cooled. The cooling process transforms some of the digestible starches into RS.
Type 4: These are man-made and formed by way of a chemical process.
As far as the above classification is concerned, different types of resistant starch can be contained in the same food substance. Many commonly consumed plant food products are high in resistant starch. These are raw potatoes, cooked and then cooled potatoes, green bananas, various legumes, cashews and raw oats.
Health benefits of RS
Many studies in humans show that resistant starch can have powerful health benefits. Thus, RS serves as food for the non-hostile bacteria which are present in the large intestine and increase production of short-chain fatty acids such as butyrate that serve as fuel for the cells there.
Resistant starch helps to reduce the pH level, and also prevent inflammation. This results in lowering the risk of colorectal cancer. Because of its therapeutic effects on the large intestines, RS can be used to control inflammatory bowel diseases such as Ulcerative Colitis and Crohn’s Disease, constipation, diverticulitis and diarrhoea. Resistant starch enhances insulin sensitivity, lowers blood sugar levels and helps control some problems in people with diabetes. By improving insulin sensitivity and lowering blood sugar, resistant starch may help one avoid a number of chronic diseases and, hence, may make you live both longer and better.
Resistant starch has fewer calories than regular starch and may increase feelings of fullness and help people eat less and lose weight. Resistant starch may contribute to colon health by increasing regularity and reducing pH for the cells of large intestines to thrive. It helps to treat diarrhoea when delivered in oral rehydration solutions to people suffering from cholera, rotavirus and other diarrhoeal diseases. The SCFAs that are not utilised by the cells of the large intestines enter the blood stream, travel to the liver and move to the rest of the body where they exert additional anti-inflammatory effects.
Butyrate plays a role as a powerful anti-inflammatory factor for cells of the large intestines and functions to improve the integrity of the digestive tract by reducing intestinal absorption and, hence, keeps toxins in the gut and out of the bloodstream. Butyrate can reverse abnormal changes in the body and can affect gene expression which may induce cell cycle arrest and naturally programmed cell death.
Processing and consumption of RS
Processing of food containing RS may lead to the breaking down of the structural barriers to digestion and, hence, reducing resistant starch content. Whole grain wheat may contain approximately 14 per cent RS, but when milled may contain only two per cent. RS content of cooked rice may decrease due to grinding or cooking. Cooling of cooked potato overnight increases the amount of RS. Resistant starch is found naturally in all starch-containing foods. Factors influencing the content of RS in foods include the initial quantity and type of starch present, how the starchy food is processed, cooked and stored and how it is ingested.
There are two ways of consuming resistant starches. That is by directly getting them from your diet or by taking them as supplements. Americans consume approximately three to eight grams of resistant starch per day, with an average daily intake of 4.9 g. In Africa and Ghana for that matter people who consume whole grains and unrefined food products are likely to consume about 30-40 g/day. It is 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 fibre of 25-38 grams per day. Individuals are encouraged to have greater consumption of foods that naturally contain resistant starch. This call is necessary in our part of the world especially because people are increasingly resorting to more refined foods rather than the unrefined. Resistant starch may function as a mild laxative and can lead to flatulence when taken at high doses. Therefore caution must be taken when being taken in large doses.
On the whole however, the health benefits of RS cannot be over-emphasised; therefore they should be patronised with the right quantities and form such that, just as it provides an array of health benefits, it does not also in itself translate in adverse health challenges for consumers.
The writer is with the Department of Nutrition and Dietetics, School of Biomedical and Allied Health Sciences,
College of Health Sciences, University of Ghana.