Resistant Starch — This Type of Fiber Can Improve Weight Control and Insulin Sensitivity

September 2012 Issue

Resistant Starch — This Type of Fiber Can Improve Weight Control and Insulin Sensitivity
By Jill Weisenberger, MS, RD, CDE
Today’s Dietitian
Vol. 14 No. 9 P. 22

Perhaps most widely recognized for promoting intestinal regularity, fiber also receives credit for helping protect people from coronary heart disease, stroke, hypertension, and diabetes or becoming obese. Additionally, fiber-rich foods protect against colorectal cancer and other intestinal disorders.1

Fibers are commonly classified as soluble or insoluble, though recognition is spreading that a fiber’s solubility doesn’t determine its physiological function. Other properties, such as viscosity and fermentability, may be more important. Naturally occurring resistant starches are a group of low-viscous fibers that are slowly fermented in the large intestine.

As their name suggests, resistant starches are starches that resist digestion in the small intestine. Their definition is “the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals.”2 Starch polymers are present in granules in plants and exist as either a straight chain (amylose) or a branched chain (amylopectin). The structure of both the granules and polymer chains affect the starch’s digestibility, making some more digestible than others.

Resistant starches are classified according to structure or source, as follows2,3:

• RS1 is physically inaccessible to digestive enzymes. Its sources include whole or partially milled grains, seeds, and legumes.

• RS2 resists digestion because of the granule’s nature. Sources include raw potatoes, underripe bananas, some legumes, and high-amylose starches, such as high-amylose corn.

• RS3 is produced in the cooking-cooling process. Sources include bread, tortillas, cooked and cooled potatoes, rice, and pasta.

• RS4 is a chemically modified starch found in a wide range of products.

Healthy Gut
Like other fibers, resistant starches make their way to the large intestine where they act as prebiotic fibers and serve as food for microbes. Intestinal bacteria ferment resistant starches, producing beneficial short-chain fatty acids (SCFAs) and improving the environment for healthful bacteria to thrive, explains Christine Pelkman, PhD, a senior scientist at Ingredion Incorporated, which produces the Hi-maize resistant cornstarch product.

“Because resistant starch is slowly fermented, it’s more tolerable at much higher doses and with less gas production than other fibers,” Pelkman says. These helpful bacteria have many functions, including producing vitamins, detoxifying potential carcinogens, and activating health-promoting compounds. For example, cruciferous vegetables contain glucosinolates that gut bacteria convert into isothiocyanates, the bioactive compounds.

The SCFAs produced by bacterial fermentation are butyrate, proprionate, and acetate. These fuel colonocytes that stimulate colonic blood flow, promote colonocyte proliferation, increase tone, and reverse the atrophy associated with fiber-poor diets.2 Butyrate in particular may affect gene expression and induce apoptosis, or normal programmed cell death, which further decreases the risk of developing colon cancer.4

The SCFAs also lower the pH of the feces.2 Reduced fecal pH is a marker of colonic health and reduced risk of colon cancer. Studies with both humans and animals show that resistant starches increase fecal weight,2,5 a characteristic thought to help treat and prevent constipation and lower the risk of colon cancer, possibly because of decreased contact between the potential carcinogens and the colon wall. A study comparing the effects of a diet high in resistant starch (39 g/day) to a low resistant starch diet (5 g/day) in 11 men and women found the greater the intake of resistant starch, the greater the increase in fecal output.6 Though significant, the bulking effect of resistant starch isn’t likely as great as the effect of wheat bran and other nonstarch polysaccharides.5

Beyond the Colon
• Weight control: Emerging research suggests that resistant starches may help with weight control. Dietetic professionals routinely advise clients to increase their fiber intake to stave off hunger, but not all fibers may produce the same satiating effects. In a randomized double-blind crossover study, Willis and colleagues examined the satiety-producing effects of four fibers incorporated into muffins. The polydextrose-containing muffin had little effect on satiety, whereas muffins made with resistant starch and corn bran exhibited the greatest effect.7 Other studies suggest that resistant starch can increase satiety and decrease food intake,8,9 but not all studies confirm these results.6

However, Mary Ellen Caldwell, RD, LD, CLT, of Professional Nutrition Therapists in Dallas, sees results with her clients who include resistant starches in their calorie-controlled diets. “It’s easy to incorporate foods with resistant starch,” Caldwell says. “It’s easy to include cooked and cooled starches, beans, and others.”

In addition to resistant starches that occur naturally in foods, products such as Hi-maize can be used as a flour replacement or supplement to increase intake. Caldwell says some of her patients bake with Hi-maize by replacing a portion of the flour called for in a recipe, and one client sprinkles it on oatmeal. Caldwell encourages her patients to include some form of resistant starch in each meal to increase satiety. Compliance is very good, she adds.

Foods containing resistant starches also may aid in weight control because they’re less calorically dense. As resistant starches are fermented in the colon with the production of SCFAs and gases, some of the calories are lost.

• Insulin sensitivity and glucose control: Resistant starch escapes digestion in the small intestine, so it doesn’t contribute to blood glucose levels. Studies also suggest that resistant starch can reduce insulin resistance. One study showed that overweight or obese men (but not women) experienced significant improvements in insulin sensitivity after consuming 15 to 30 g of Hi-maize resistant cornstarch per day for four weeks.10

The exact mechanisms for improved insulin sensitivity haven’t been elucidated, says Mindy Maziarz, MS, RD, LD, who’s conducting resistant starch research at Texas Woman’s University. She notes that the elevated free fatty acids (FFAs) that frequently occur with hyperglycemia may be involved in reducing insulin sensitivity. “SCFAs produced by the fermentation of resistant starch in the colon may lower FFA plasma concentrations, thus improving insulin sensitivity,” Maziarz says. “Resistant starches also may affect insulin sensitivity by changing adipokines associated with adipose metabolism.” Additionally, they may increase the gastrointestinal hormones glucagonlike peptide 1 and peptide YY, she adds.

“Studies with sufficient amounts of Hi-maize resistant starch have shown lower post-meal glucose and insulin levels, increased satiety, and decreased hunger postfood and meal consumption,” says Hope Warshaw, MMSc, RD, CDE, author of Diabetes Meal Planning Made Easy and consultant to Ingredion. These studies have even shown lower caloric intake at the next meal as well as after 24 hours, she adds. “The slow fermentation of resistant starch along the large intestine may be responsible for some of these effects.”

High-amylose cornstarch is the most widely studied resistant starch source, though some studies have looked at the effects of resistant starch from potatoes, bananas, and wheat. It’s not clear whether generalizations can be made about resistant starches as a class based on the research involving only one source.

Helping Clients Boost Intake
Americans consume approximately 3 to 8 g of resistant starch per day, with an average daily intake of 4.9 g.2 A good goal is to consume 15 to 20 g per day, Warshaw says. To help patients and clients reach that goal, RDs should start by encouraging greater consumption of foods that naturally contain resistant starch (see table below).

Second, seek out pastas, breads, flour, and other foods with added Hi-maize resistant starch, Maziarz says. “It’s important for consumers to check the ingredient label for ‘cornstarch’ or ‘resistant cornstarch,’” she adds. Finally, “Consumers can purchase resistant starch and add it to baked goods, smoothies, sauces, and casseroles.”

— Jill Weisenberger, MS, RD, CDE, is a freelance writer, nutrition consultant, and certified diabetes educator in southeastern Virginia and the author of Diabetes Weight Loss — Week by Week.

Resistant Starch Content of Commonly Eaten Foods2

Food	Resistant Starch (g)
Underripe banana, 1 medium	4.7
Rolled oats, 1/4 cup, uncooked	4.4
Oats, 1 cup, cooked	0.5
Pearl barley, 1/2 cup, cooked	1.9
White beans, 1 cup, cooked	7.4
Lentils, 1/2 cup, cooked	3.4
Pumpernickel bread, 1 ounce	1.3
White pita bread, white, 2 ounces	1.1
Whole wheat bread, 1 ounce	0.3
Potato chips, 1 ounce	1.0
Hi-maize resistant starch, 1 T	4.5

References
1. Anderson JW, Baird P, David RH Jr, et al. Health benefits of dietary fiber. Nutr Rev. 2009;67(4):188-205.

2. Murphy MM, Douglass JS, Birkett A. Resistant starch intakes in the United States. J Am Diet Assoc. 2008;108(1):67-78.

3. Warshaw H. Rediscovering natural resistant starch — an old fiber with modern health benefits. Nutr Today. 2007;42(3):123-128.

4. Nugent AP. Health properties of resistant starch. Nutrition Bulletin. 2005;30(1):27-54.

5. Ferguson LR, Tasman-Jones C, Englyst H, Harris PJ. Comparative effects of three resistant starch preparations on transit time and short-chain fatty acid production in rats. Nutr Cancer. 2000;36(2):230-237.

6. Phillips J, Muir JG, Birkett A, et al. Effect of resistant starch on fecal bulk and fermentation-dependent events in humans. Am J Clin Nutr. 1995;62(1):121-130.

7. Willis HJ, Eldridge AL, Beiseigel J, Thomas W, Slavin JL. Greater satiety response with resistant starch and corn bran in human subjects. Nutr Res. 2009;29(2):100-105.

8. Nilsson AC, Ostman EM, Holst JJ, Björck IM. Including indigestible carbohydrates in the evening meal of healthy subjects improves glucose tolerance, lowers inflammatory markers, and increases satiety after a subsequent standardized breakfast. J Nutr. 2008;138(4):732-739.

9. Anderson GH, Cho CE, Akhavan T, Mollard RC, Luhovyy BL, Finocchiaro ET. Relation between estimates of cornstarch digestibility by the Englyst in vitro method and glycemic response, subjective appetite, and short-term food intake in young men. Am J Clin Nutr. 2010;91(4):932-939.

10. Maki KC, Pelkman CL, Finocchiaro ET, et al. Resistant starch from high-amylose maize increases insulin sensitivity in overweight and obese men. J Nutr. 2012;142(4):717-723.