Introduction to Resistant Starch

Cereals are a major energy-providing food for the global population, and starch is the major energy component in cereals. Tubers and legumes are also important sources of starch in the diet. Starch is the main contributor to sufficient caloric intake in the global population, probably contributing to close to 40% of the global energy intake.

Starch is a polymer of glucose molecules. Normal starch consists of two polysaccharides, amylopectin and amylose. Amylose is essentially a linear polysaccharide with α-(1→4) linkages of D-glucopyranose units and a few branched α-(1→6) linkages. Amylopectin is a highly branched polysaccharide consisting of short linear chains connected by approximately 5% α-(1→6) branched linkages. The digestion of starch occurs partially in the mouth and predominantly in the small intestine, where pancreatic α-amylase is released and dextrinase, amyloglucosidase, α-glucosidase, and maltase are found in the brush border cells of the intestinal wall. Starch is eventually hydrolyzed to glucose, and the glucose is rapidly absorbed in the small intestine to be used for cellular energy production.

However, highly digestible starch may contribute to nutrition-related health problems through several mechanisms. First, the abundance of inexpensive starchy foods has resulted in an oversupply of calories, causing a shift from providing essential nutrients to overconsumption of energy providing nutrients, which results in obesity and related health problems. It was reported that more than 50% of the adult population in the developed world is now overweight or obese. Second, common starch-rich foods generally produce a large glycemic response, which increases the risks of type 2 diabetes and cardiovascular disease. Type 2 diabetes involves an abnormal rise in levels of blood glucose following a starch-rich meal and a delayed reduction in postprandial blood glucose levels. According to the World Health Organization, chronic high blood glucose is the third largest cause of premature mortality. Maintaining glycemic control has been established as the primary treatment goal for diabetic and prediabetic patients. Cardiovascular disease is mainly caused by atherosclerosis, which is an accumulation of cholesterol-rich necrotic tissue in the intima of blood vessels that may cause blockages of arteries through thrombosis. The cholesterol-rich necrotic tissue originates from lipoproteins that transport triglycerides in the blood. Thus, cardiovascular disease is strongly correlated with obesity. Lifestyle interventions, including dietary changes, have therefore been suggested as primary treatments to enable patients to manage their body weights and blood glucose levels.

Because blood glucose levels are directly affected by the intake of readily digestible carbohydrates, especially starch, there is an increased interest in improving the safety and health enrichment of products with low carbohydrate digestibility. Starch has different physiological effects on human health, depending on its digestion rate. According to its digestibility, starch is generally classified as being a rapidly digestible starch (RDS), slowly digestible starch (SDS), or resistant starch (RS), depending on its physiological effects after consumption. RDS induces a fast increase in blood glucose and insulin levels, whereas SDS is slowly digested throughout the small intestine, producing a low glycemic response. RS is that portion of starch that escapes digestion in the small intestine and can only be fermented in the colon.

Public health authorities and nutritionists agree that the intake of foods rich in dietary fiber provides health benefits. RS is recognized as a type of dietary fiber that can be used in foods as a functional ingredient. Studies have found that RS, which is fermented by microbes in the large intestine, can provide many health benefits, including a laxative effect, lowering the risk of developing digestive tract cancer, a reduction of glucose postprandial responses, a reduction in blood lipids levels, and changing the prebiotic capacity to allow it to function as a substrate for colon flora.

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