Resistant starch reduces the rate at which other starches in the same food (or meal) are broken down during digestion, and this reduces unhealthful spikes in blood sugar and insulin levels.

In fact, thanks to its so-called “second meal effect”, resistant starch improves the body’s response to dietary sugars and starches (glucose tolerance) for hours after a meal, and even into the next day. (Slowly-digested starches and soluble dietary fibers, such as in oats, also slow digestion of starches, to a lesser extent.)

Beans are the best food source of resistant starch: in general, the starch in beans is about evenly divided between slowly-digested starch and resistant starch. (Whole, intact grains are also substantial sources of resistant starch.)

When we eat resistant starch, it raises intestinal levels of short-chain fatty acids that appear to protect colon cells from cancer-causing genetic damage. And resistant starch enhances absorption of minerals such as calcium and magnesium: an effect also associated with reduced colon cancer risk.

Resistant starch offers a variety of benefits:

• Stabilizes blood sugar and insulin levels.
• Lowers total cholesterol and triglyceride levels
• Raises HDL (“good”) cholesterol levels.
• Promotes beneficial bacteria, and suppresses disease-causing bacteria and their toxic products.
• Promotes regularity.
• Reduces storage of dietary calories as fat.

For more on the benefits of beans, see “Beans Seen to Discourage Weight Gain and Diabetes”.

US-Chinese team links beans to reduced diabetes risk

Prior indications that beans might reduce diabetes risk received support from a recent epidemiological study.

Researchers from Vanderbilt University Medical Center and the Shanghai Cancer Institute recruited 64,227 middle-aged Chinese women with no previous history of diabetes, cardiovascular disease or cancer, surveyed their dietary habits, and examined them after an average of 4.6 years.

The authors reported that the women reporting the highest intake of legumes – beans, lentils, soybeans, and peanuts – had the lowest rates of diabetes.

The women with the highest intake levels of legumes were 38 percent less likely to have developed diabetes and those with the highest intake of soybeans were 47 percent less likely to have developed diabetes.

It is important to note that this apparent protective effect did not extend to processed soy products and pure soy protein.

As they wrote, “The association between soy products (other than soy milk) and soy protein consumption (protein derived from soy beans and their products) with type 2 [diabetes] was not significant.”

Last April and March, Harvard University researchers published the results of clinical trials, in which 42 post-menopausal women with signs of metabolic syndrome replaced red meat with either soy protein or soy nuts.

All of the women were placed on the anti-hypertension diet called DASH (Dietary Approaches to Stop Hypertension), which is rich in fruits, vegetables, whole grains, and low-fat dairy products and low in saturated fat, total fat, cholesterol, refined grains, salt, and sweets.

Both studies showed very positive results from replacing meat in the DASH diet with soy nuts, but did not display as much benefit from replacing red meat with soy protein:

“Short-term soy nut consumption reduced some markers of inflammation … increased plasma nitric oxide levels … improved glycemic control and lipid profiles in postmenopausal women with the metabolic syndrome.” (Azadbakht L et al 2007)

Sources

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• Azadbakht L, Kimiagar M, Mehrabi Y, Esmaillzadeh A, Padyab M, Hu FB, Willett WC. Soy inclusion in the diet improves features of the metabolic syndrome: a randomized crossover study in postmenopausal women. Am J Clin Nutr. 2007 Mar;85(3):735-41.
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• Park OJ, Kang NE, Chang MJ, Kim WK. Resistant starch supplementation influences blood lipid concentrations and glucose control in overweight subjects. J Nutr Sci Vitaminol (Tokyo). 2004 Apr;50(2):93-9.
• Robertson MD, Currie JM, Morgan LM, Jewell DP, Frayn KN. Prior short-term consumption of resistant starch enhances postprandial insulin sensitivity in healthy subjects. Diabetologia. 2003 May;46(5):659-65. Epub 2003 Apr 24.
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• Villegas R, Gao YT, Yang G, Li HL, Elasy TA, Zheng W, Shu XO. Legume and soy food intake and the incidence of type 2 diabetes in the Shanghai Women's Health Study. Am J Clin Nutr. 2008 Jan;87(1):162-7.
• Zhang WQ, Wang HW, Zhang YM, Yang YX. [Effects of resistant starch on insulin resistance of type 2 diabetes mellitus patients]. Zhonghua Yu Fang Yi Xue Za Zhi. 2007 Mar;41(2):101-4. Chinese.
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