Resistant starch is simply starch that resists digestion and reaches the large intestine. Americans already consume about 5g of resistant starch daily,1 in foods such as unprocessed whole grains (in which the starch is protected from digestion by the seed or shell or hull of the grain), beans, bananas and bread. High amylose corn is another source for natural resistant starch.
Resistant starch is a natural white cornstarch powder that is 55-60 per cent insoluble dietary fibre. By comparison, whole wheat contains 12 per cent fibre,2 with about 10 per cent insoluble fibre. One tablespoon (about 9.5g) delivers a little more than 5g of dietary fibre, (more than the amount of fibre in a bowl of oatmeal). It classifies as a natural RS2 type of resistant starch.
How to use it
National Starch Food Innovation's Hi-maize brand resistant starch is insoluble and is a dry white powder. It is being sold to consumers in both powder form (for home baking and supplement consumption); in medical foods targeting diabetics; and in ready-to-eat baked goods, pasta and bakery mixes.
It easily replaces flour in recipes and food formulations. It can replace up to 20 per cent of the flour in snacks, pasta and baked goods such as cookies, pancakes, muffins, tortillas and cakes. Most formulations require little adjustment, except for the addition of a little bit more water and the addition of vital wheat gluten in bread and pasta.
The powder can be added to smoothie/shake mixes or stirred into oatmeal or yoghurt. As an insoluble fibre, it will not dissolve in beverages, soup or dairy products, nor will it provide thickening (unlike regular cornstarch). It tastes like bland cornstarch and has a minimal impact on the taste or texture of foods.
How it works
When resistant starch replaces flour in foods, the glycaemic response and the insulin response of that food goes down. The higher the proportion of flour that is replaced, the lower the glycaemic and insulin responses will be. While the reduced glycaemic impact is beneficial, it is not the primary mechanism for improved insulin sensitivity.
Hi-maize's resistant starch (55-60 per cent) reaches the large intestine, where it is completely fermented by resident bacteria in the gut, including Bifidobacterium and Lactobacillus acidophilus. The fermentation produces short-chain fatty acids, predominately butyrate, propionate and acetate. For an unknown reason, fermentation of resistant starch produces more butyrate than any other fibre tested.2 For example, the same quantity of inulin will produce less than half of the amount of butyrate than resistant starch will produce, even though both fibres are fully fermented. This difference in chemical by-products is believed to contribute to resistant starch's unique metabolism benefits.
Four clinical trials have been completed examining the impact of Hi-maize resistant starch on insulin sensitivity. Three of the studies followed a similar design — participants were given the resistant starch as a powder supplement and instructed to mix it into their regular diet. As a control, they were given a portion of highly digestible starch so that the glycaemic impact would be the same between the test diet and the control diet. Thus, the only difference was the amount of resistant starch that reached the large intestine. Any physiological benefits found would be the result of the large intestinal fermentation — not differences in blood-sugar release or glycaemic impact.
Two studies showed that Hi-maize significantly improved insulin sensitivity in healthy people.3,4 The latest study in healthy people, published in the American Journal of Clinical Nutrition6 found that when people ate 50g/day (containing about 28-30g dietary fibre) for four weeks, their insulin sensitivity improved by 14 per cent when measured by the gold standard for measuring insulin sensitivity (the hyperinsulinemic euglycemic clamp). When measured by their glucose and insulin response to a standardised meal, their insulin sensitivity improved by 33 per cent.
The preliminary results of the third study were presented at the Diabetes UK Annual Conference in March 2009, and showed that overweight individuals with insulin resistance responded much more strongly to Hi-maize than individuals without metabolic syndrome.5 They consumed 67g/day (containing 40g dietary fibre) in addition to their regular diet. At the end of eight weeks, their muscle insulin sensitivity improved by 24 per cent, their liver insulin sensitivity improved by 54 per cent and there was a 68 per cent increase in glucose absorbed into muscle tissue in the forearm. They also had reduced fasting insulin levels, reduced postprandial insulin responses to a standardised meal and significantly lower levels of fasting nonesterified fatty acids.
"These improvements are actually bigger than you get with most blood glucose lowering drugs," said Dr Denise Robertson, principal investigator at the Postgraduate Medical School at the University of Surrey in the United Kingdom.
A fourth study, published in the Chinese Journal of Preventive Medicine,6 showed that type 2 diabetics had an 11-15 per cent improved insulin sensitivity and significantly lower fasting blood sugar following the dietary consumption of 30g/day for four weeks. Instead of being added to the diet as a supplement, Hi-maize resistant starch was delivered within a noodle or steamed bread.
How much is needed?
The vast majority of Americans need to eat more dietary fibre, so any amount of Hi-maize resistant starch added to the diet would be beneficial. Because it is fermented very slowly, individuals can easily consume the entire recommended intake of dietary fibre as resistant starch without negative digestive side effects. The most common side effect is regularity. Even with extremely large doses, it does not cause bloating, cramping or other digestive-distress symptoms common to other types of soluble fermentable fibres in healthy individuals.
In regard to improving insulin sensitivity, studies have shown that 30-100g/day improved insulin sensitivity. A little more than 3 level tablespoons would deliver 30g of fibre, but insulin-resistant individuals would likely need more to feel the effects. Additional studies are needed to determine the dose response and minimum quantity for insulin sensitivity benefits.
Rhonda Witwer is director of senior business development, nutrition, for National Starch Food Innovation. www.foodinnovation.com
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