Starch in foods contribute a major portion of calories in human diets and most of the population in the world depend on rice, wheat, and other cereals as their staple diet. Almost all cereals contain high levels of starch and normal starch, when digested in the gastrointestinal tract, yields readily utilizable glucose which is absorbed across the intestinal wall for serving as energy source for the living cells. It is only during the last 3-4 decades that sugar and other non-starch carbohydrates have become major sources of energy because of the predominance of industrially processed food products in the daily diet. The modern weight watching community has invariably targeted the starch in their attempts to cut down weight and they may be right in so far as all products from the industry contain refined starch ingredients devoid of the innate nutrients like germ, bran and others. But all starches do not deserve to be condemned and the importance of resistant starch, a form of starch molecules different in physical structure from the conventional ones, can be extremely healthy for humans as being brought out by many studies.
Many consumers may be unaware of the existence of resistant starch which is present in almost all foods one consumes to varying extent. The name is derived from the fact that it resists digestion in the small intestine and ends up in the large intestine for doing its good work. Many nutritional experts believe that resistant starch should be considered as the third form of dietary fiber, the other two being soluble and insoluble fibers. It is generally agreed that there are four different types of resistant starches, all capable of functioning as dietary fiber with varying efficiency. Starch that cannot be accessed physically from the sources like seeds, legumes and whole grains constitutes the first category known as RS1 while starch present in uncooked materials like uncooked potato, raw green banana flour and high amylose corn comes under RS2. During cooking or processing resistant starch is generated like in cooked legumes, baked bread, corn flakes and others, known as RS3 while chemically modified starches like etherized, esterified and cross bonded starches, not occurring in nature constitute the RS4 category.
In nature resistant starch occurs at varying levels in foods like cooked Navy beans ( 10 gm per half cup), raw banana (5 gm per one fruit), cold potato ( 3 gm per half inch diameter sample), cooked lentils (2.5 gm per half cup), cold pasta (2 gm per cup), pearled barley (1.5 gm per half cup) and in smaller amounts in many others. One of the beneficial attributes of these starches is that they help the friendly microbes in the large intestine to grow and produce the much needed short chain fatty acids including butyrates in abundance which are implicated in healthy growth of colon cells, acting as anti-inflammatory and anti-carcinogenic agents, abetting better absorption of Calcium and Magnesium, reducing cholesterol build up, over all reducing the intestinal pH and generation of potentially harmful secondary bile acids, ammonia and phenols.
The foods which are rich in resistant starch seems to have a role in aiding digestion since they provide fuel for bacteria in the colon that aid the process. Resistant starch has become a focal area of interest lately because they have been recognized by global agencies like the Food and Agricultural Organization (FAO) and World Health Organization (WHO). Some researchers even claim that resistant starch is able to cause shrinkage of fat cells in the human body, simultaneously increasing the muscle mass. According to the findings by scientists from University of Colorado based on a massive study those who consumed most of their carbohydrates from whole grains, fruits and vegetables were slim while others who ate the least carbohydrates tended to over-weight. If WHO findings are true, resistant starch may be the future "weight buster" and "Health Mascot" as it promotes satiety while decreasing the cravings for energy- and fat-rich foods.