Why Eating Resistant Starches May Bolster Health

Resistant starches come in 5 classes, one of which can be found in unripe (green) bananas. Photo Credit:  Mnn.com

       There's been quite a lot of buzz lately over prebiotics, probiotics, gluten-free eating and low-carb diets. Carbohydrates really take a lot of flack for being a contributor to type two diabetes melitus and the obesity epidemic, but what about complex starches that fall under the umbrella of this controversial macronutrient?  What about resistant starches? A resistant starch, as defined by the American Association of Cereal Chemists, is "the starch fraction that escapes digestion in the small intestine of healthy humans." Essentially, what a resistant starch is "resisting" is the enzymatic breakdown and fractionation of strands of bonded glucose that typically occurs in the small intestine through the process of hydrolysis. Resistant starches occur naturally but they can also be produced through the application of cooking techniques or chemical modification. A recent review from the scientific journal Advances in Nutrition differentiates among the 5 types of resistant starches (RS). RS1 has a great deal of its starch trapped or contained in such a way that intestinal enzymes called amylases cannot reach the starch molecules because of the physical barrier of an impenetrable cell wall (seeds, whole grains, legumes, peas). RS2 are the raw/unripe starches that can be found in raw potatoes and green bananas, and this starch loses its resistance when the heat of cooking gelatinizes the starch, thermally breaking bonds so that the glucose units are released. RS3, called retrograde starch, is moist and digestible at room temperature, though cooling renders it indigestible by intestinal enzymes. This type can be found in chilled, cooked pasta/rice/potatoes. RS4 is chemically altering a starch so that the starch's bonds withstand cooking at high temperatures and remain unbreakable by digestive enzymes. These are being further developed for application in commercial products and are already an addition to several available specialty food products to decrease carbohydrate and calorie content. RS5 is bound to a lipid so that hydrolysis cannot physically occur. The result is an indigestible starch component.

So if a consumed starch isn't being digested, what is happening to it? Like fiber, the indigestible resistant starch is passing through the small intestine and is used as a substrate by bacteria of the small intestine for fermentation. This process of fermentation produces several byproducts that, according to the review of research, could be quite beneficial to the health of the consumer by protecting the epithelial cells of the colon and promoting normal growth and development. Given a substrate, also referred to as a prebiotic, protective gut bacteria apply fermentation for sustenance in the colon, continually producing products (such as short chain fatty acids) that directly influence the large bowel, potentially positively influencing the health of their host and possibly even preventing related disease states such as inflammatory bowel disease and colon cancer. Even more, the published review suggests that conditions such as type 2 diabetes and obesity may be attenuated with moderate intake of resistant starch, due to it's slow digestion and absorption, promoting a slow glycemic response, lengthened satiety, and decreased intake at meals.

Though the exact mechanisms of action of resistant starches need to be investigated further in order to completely understand their positive associations, it can be assumed that resistant starches are a beneficial addition to the diet through their fiber-like effect on the microbiome, on glycemic response, and on appetite. Recommendations have been made for consumers to aim to get 6 grams of resistant starch per meal. Though the review states that Americans are shy of this average daily goal of 18 grams by nearly 13 full grams (Americans as a whole tend to consume low amounts of resistant starch per day, only about 5 grams) an increased awareness of practical food swaps and the introduction of products developed to contain modest amounts of resistant starch can increase the dietary intake. Foods high in resistant starch include chickpeas, yams, lentils, kidney beans, uncooked oats, cornflakes and chilled rice/pasta among many others. Certain commercial products are also being developed that contain high amounts of resistant starch, and these can be found online and in select food stores.  Though several promising research studies show inverse relationships between resistant starch consumption and risks associated with diabetes, obesity, inflammatory bowel disease, and colon/rectal cancer, the research findings are not yet well understood and eating a balanced diet including whole grains, fruits, vegetables, and legumes should be considered the best way to obtain both resistant and digestible starches that play a role in total health.


Take a glance at the origional review article HERE! Advances in Nutrition