Because a variety of starch or starch degradation products can be classified
as resistant starch, they will not deliver the same health benefits.
Adding healthful ingredients to bakery items is becoming more than just a passing fad. Consumers want products that taste good, but also those that provide nutritional benefits. And, for many bakers, resistant starch not only serves as a readily usable substitute for flour, but delivers the functional benefits consumers' seek.
Yet, why aren't more bakers turning to resistant starches for their nutritional and functional value? Probable reasons include a lack of understanding of what resistant starch is, how it's used and the health impact associated with each type.
Simply put, resistant starch is defined as the starch and starch by-products from digestion that are not absorbed in the small intestine of healthy individuals. Understanding how resistant starches relate to the larger category of carbohydrates can be beneficial. Generally speaking, carbohydrates can be divided into two categories: those that are digested in the small intestine and those that are not.
The first category, consisting of sugar and most starches, are those that are rapidly digested and absorbed in the small intestine, and therefore used for short-term energy needs or stored. These sugars and starches are referred to as available, digestible or glycemic carbohydrates.
Fiber, by definition, falls into the second category — those referred to as unavailable, non-digestible or non-glycemic carbohydrates. Fiber passes through the small intestine and provides no short-term energy, but instead “has a variety of physiological effects in and emanating from the large bowel,” according to National Starch Food Innovation, Bridgewater, N.J. So, without being absorbed, resistant starch passes through the small intestine into the large intestine and is fermented in the colon.
Basically, resistant starch is a type of dietary fiber and is recognized by many public health authorities, such as the World Health Organization, the Food and Agricultural Organization and the U.S. National Academy of Sciences as a beneficial carbohydrate.
Four categories of resistant starches exist (see chart). In category four, for instance, where resistant starches have been produced through chemical, thermal or acid-treated modification, the starch differs mainly in its physical characteristics, and especially in its water-holding capacity, notes Susan Gurkin, bakery snacks and cereals category marketing manager, Cargill Texturizing Solutions, North America, Minneapolis.
As a result of the huge variability of structural differences among resistant starches, not all types deliver the same health benefits. “One type of pregelatinized RS4 resistant starch has been shown to not reduce the glycemic impact of foods. This means that physiologically, it doesn't even reach the large intestine. So, while it is being sold as ‘resistant starch,' it doesn't live up to its name physiologically. This is a prime example of why human clinical studies are so important to confirm the physiological response,” says Rhonda Witwer, senior business development manager, nutrition, National Starch Food Innovation.
In another example, Witwer describes a type of RS3 resistant starch that reaches the large intestine, but is barely fermented. And, fermentation is reportedly the key driver behind turning on the satiety hormones, which helps promote a feeling of fullness. Thus, a resistant starch that is minimally fermented won't help induce a feeling of fullness, which can help with weight loss.
A variety of healthful benefits have been attributed to resistant starch. High amylose corn starch improves insulin sensitivity and glycemic management when replacing flour by reducing the short term glycemic response, or the short term spike in blood sugar; reducing the short term insulin response, or the spike in insulin produced by the body to manage the spike in blood sugar; and significantly improving insulin sensitivity that lasts well beyond the immediate eating occasion, Witwer notes.
“I want to emphasize the importance of improved insulin sensitivity and glycemic management with the dietary consumption of high amylose resistant starch,” Witwer adds. “Baked products have been hit particularly hard by the growing awareness of the high glycemic impact of most processed baked items. People have stopped consuming as many bakery items as they seek to lose weight, as they utilize glycemic control to manage their energy, and as they become concerned about developing diabetes. Many of them haven't yet added processed carbohydrates back into their diet since the low-carb fad.”
“Many dietary fibers have been shown to reduce glycemic and insulin response, so this is relatively common,” Witwer says. “However, reduced glycemic index diets do not correlate to improvements in insulin sensitivity. High amylose corn starch's improvement in insulin sensitivity is very unusual for dietary fibers. It is believed that the fermentation (and not reduced glycemic response) creates this benefit. Most other insoluble fibers are not fermented, and thus cannot possibly trigger this benefit.”
Other health benefits associated with resistant starch include improvements in energy management, digestive health, fat metabolism, mineral absorption and immune system support, among others. Resistant starches also have been beneficial in managing diseases, such as ulcerative colitis and colorectal cancer.
Animal studies have shown that consumption of resistant wheat starch produces higher levels of beneficial short-chain fatty acids, lowers liver cholesterol and increases serum HDL (“good”) cholesterol, notes Kyungsoo Woo, Ph.D., principal scientist, MGP Ingredients, Atchison, Kan. In addition, resistant wheat starch typically contains greater than 90 percent total dietary fiber. Thus, bakers using a minimum of 2.5 g or 5 g fiber per serving can claim a good or excellent source of fiber, respectively.
“It is important for manufacturers to look beyond just the ‘fiber' benefits of resistant starch and consider the ingredient for its satiety characteristics and its contribution to weight management — especially in baked goods,” Gurkin says.
As clinical trials continue and as the science on resistant starch continues to evolve, bakers will be best served by working with their ingredient suppliers to unravel the mysteries surrounding this ingredient type.
|RS1||Physically inaccessible starch, such as seeds and legumes and unprocessed whole grains|
|RS2||Occurs in granular, non-gelatinized sources, such as green bananas, uncooked potatoes and high amylose corn (maize)|
|RS3||Forms when starch-containing foods are cooked and cooled, such as in bread, cornflakes and cooked and chilled potatoes|
|RS4||Starches that have been chemically modified to resist digestion|