RESISTANT STARCH: An Ameliorating Substance

Starches are long chains of glucose that are found in grains, potatoes and various foods but not all of the starch you eat gets digested, certain starches are resistant to digestion.  Resistant starch is a carbohydrate that resists digestion in the small intestine and ferments in the large intestine. As the fibres ferment they act as a prebiotic and feed the good bacteria in the gut. Since resistant starch is not digested in the small intestine, it doesn’t raise glucose. Gut health is improved as fermentation in the large intestine makes more good bacteria in the gut which eventually improves glycaemic control. Other benefits include increased feeling of fullness, prevention of obesity, weight management, treatment and prevention of constipation, decrease in cholesterol levels and lower risk of colon cancer. In short, the inclusion of resistant starch in diet induces complex interactions between microbiota, dietary components, colonic epithelium, the immune system and the nervous and endocrine systems.

Foods that contain resistant starch include:

·         Plantains and green bananas (as a banana ripens the starch changes to a regular starch)

·         Beans, peas, and lentils (white beans and lentils are the highest in resistant starch)

·         Whole grains including oats and barley

·         Cooked and cooled rice

The amount of resistant starch changes with heat. Oats, green bananas, and plantains lose some of their resistant starch when cooked as another type of resistant starch is made in the cooking and cooling process. Cooked rice that has been cooled is higher in resistant starch than rice that was cooked and not cooled.

TYPES OF RESISTANT STARCH

There are currently 5 types of resistant starch. More than one type of resistant starch can be present in a single food.

Type I Starch is synthesized in the endosperm of cereal grains or seeds and starch granules are surrounded by protein matrix and cell wall material. These physical structures prevent water penetration into the starch in the matrix. Therefore, the starch does not have adequate moisture to readily gelatinize and swell. Without proper swelling to expose the starch molecules, the starch is not readily susceptible to enzymatic hydrolysis

Type II Uncooked potato starch, green banana starch, gingko starch, and high-amylose maize starch, which display the B- or C-type polymorph, are highly resistant to enzymatic hydrolysis. High-amylose starch produced by mutation of the amylose-extender gene and the gene encoding starch branching-enzyme I, this starch displays a high gelatinization temperature, above the boiling point of water. After boiling or cooking at a temperature below its gelatinization temperature, this type of starch retains its crystalline structure and remains resistant to enzymatic hydrolysis.

 Type III resistant starch (RSIII) is retrograded amylose and starch .Because amylose molecules have linear structures, they have a great tendency to form double helices, particularly near refrigeration temperatures (4–58 °C) and with adequate moisture content and also has high gelatinization temperatures, up to 170 °C. Starchy foods are stored, particularly in a refrigerator, amylose molecules and long branch chains of amylopectin form double helices and lose their water-binding capacity. The double helices of starch molecules do not fit into the enzymatic binding site of amylase, thus they cannot be hydrolysed by this enzyme.

 Type IV resistant starch (RSIV) is a chemically modified starch, formed either by cross-linking or by adding chemical derivatives. Adding a chemical derivative to starch, such as octenyl succinic groups or acyl groups, changes the structure of the starch and partially restricts the enzymatic hydrolysis of the starch molecule, resulting in resistant starch. A region of the starch without the derivative can be hydrolysed by bacteria amylases and fermented to produce short-chain fatty acids.

Type V. When starch interacts with lipids, amylose and long branch chains of amylopectin form single-helical complexes with fatty acids and fatty alcohols. When the linear starch chain is in a helical-complex structure with the complexed fatty acid in the cavity of the helix, starch binding and cleavage by amylase are prevented.

HEALTH BENEFITS OF RESISTANT STARCH

One of the main reasons why resistant starch improves health is that, it feeds the friendly bacteria in your intestine and increases the production of short-chain fatty acids like butyrate.

Prevention of colon cancer

Resistant starch has received attention for potential prevention of colon cancer and inflammatory bowel diseases,consumption of diets with abundant fibre is believed to protect against colorectal cancer .The most common hypotheses by which colon carcinogenesis may be altered by resistant starch  focus on the alteration of the water-holding capacity of the fecal stream, modification of the microbiota, and increasing SCFA ( short chain fatty acid) production. This seems to be the most promising theory on the impacts of dietary resistant starch on the production of SCFAs and changing the microbiota. SCFAs (acetate, propionate, and butyrate) are increased in amount , these are important metabolites in maintaining intestinal homeostasis .

Butyrate, an end-product of microbial fermentation of resistant starch and the primary energy source for colonocytes, is actively transported into cells by a Na+ -dependent cotransporter . This cell membrane transporter serves as a tumor suppressor gene and is epigenetically silenced by hypermethylation in human aberrant crypt foci (a precancerous lesion) and colorectal cancer . Butyrate has been of particular interest because of the role this molecule plays in colonic epithelial metabolism and differentiation and its influence on signaling pathways that regulate mucosal physiology it have the ability to modify expression of genes that control cell cycle and apoptosis and function to suppress the development of pre-neoplastic and neoplastic phenotypes in vitro Furthermore, butyrate exerts protective effects against intestinal mucosal inflammation, a component of inflammation-mediated colorectal cancer, through apoptosis of T lymphocytes and inhibition of inducible nitric oxide synthase in colonic epithelium.

 PREVENTION/ THERAPY  OF METABOLIC DISEASES

DIABETES

Lifestyle modifications are found to be more effective than pharmacological interventions in delaying the onset of type 2 diabetes . One such lifestyle change is the replacement of ordinary starch in foods with resistant starch, owing to its low glycemic index. Moreover, consuming less digestible starches may decrease glycemic response to a subsequent meal, the “second meal effect.” Ten healthy individuals who ate high-amylose starch at breakfast showed decreased blood glucose response to a lunch containing highly digestible carbohydrate, compared with eating high-amylopectin starch at breakfast . Consequently, replacing ordinary dietary starch with resistant starch contributes to diabetes management.

OBESITY

Overconsumption of energy is proposed to be responsible for the obesity. Increasing consumption of resistant starch are proposed to provide many of the benefits of dietary fiber thus  also aid weight management and beneficially influence body composition .Accumulating evidence from rodent studies suggests that replacing rapidly digestible starch with resistant starch reduces body weight. First, because of the lower calorie content, replacing rapidly digestible starch with resistant starch reduces the energy density of the diet . Second, incorporating resistant starch into a meal may augment feelings of satiety . In rodent models, adding resistant starch to the diet increased secretion of the putative satiety hormones GLP-1 and PYY, suggesting that it might augment satiety. Third, resistant starch may influence body weight by increasing energy expenditure or fat oxidation. However, currently, little evidence supports this hypothesis and several studies have failed to show that resistant starch increases energy expenditure or fat oxidation.

Addition of resistant starch to the diet have enormous ameliorating health effect. However, it is important to note that it may take 2–4 weeks for the production of short-chain fatty acids to increase and to notice all the benefits .Thus, there’s no point in taking much excess amounts .

Miss: AAN MERY BOSCO, III PHARM.D