By Craig Weatherby
Legumes rank among the most overlooked health-boosters.
Beans – black, kidney, pinto, garbanzo, string beans, and more – are the best known members of the legume family, which includes peanuts.
Their healthful properties stem primarily from four factors in them: antioxidants, omega-3s, soluble fiber, and special “resistant” starch.
(The omega-3s in beans are a short-chain type called ALA, and humans can only convert about five percent of ALA into the essential long-chain forms – DHA and EPA – found in human cells and seafood.)
Among the healthful factors in beans, the least-known but potentially most important factor is resistant starch.
Beans lower the glycemic index of other foods consumed in a meal, and blunt blood sugar spikes for up to 24 hours afterward.
Last year, a controlled clinical trial from Canada's University of Toronto showed that diabetics who ate at least one cup of beans or other legumes daily improved their glycemic (blood sugar) control and likely reduced their risk for coronary heart disease (Jenkins DJ et al. 2012).
As its name suggests, resistant starch resists the digestive processes that break regular starch down into sugars … but it's not a true fiber, either.
Legumes (beans, lentils, split peas, string beans) contain the highest percentages of resistant starch, by far, followed distantly by whole, unprocessed grains.
You can raise the percentage of resistant starch in fresh-baked bread or in cooked, rice, pasta and potatoes just by cooling them quickly … a process called “retrogradation”.
When you heat these foods, the digestible starchy adopts a gel-like form, and when you cool it quickly, it morphs into digestion-resistant forms.
Now, an evidence review from the University of Colorado Cancer Center supports the idea that resistant starch helps the body resist colorectal cancer.
Beans vs. colon cancer
Once in the bowel, resistant starch does some valuable things:
Lowers bowel pH (more acidic).
Slows digestive “transit time”, thereby curbing spikes in blood sugar levels.
Boosts production of short-chain fatty acids that promote the growth of beneficial bacteria and discourage pathogenic bugs.
Resistant starch appears to discourage colon cancer by killing pre-cancerous cells and reducing the inflammation that can promote cancer.
“You have to consume it at room temperature or below – as soon as you heat it, the resistant starch is gone. But consumed correctly, it appears to kill pre-cancerous cells in the bowel,” said co-author Janine Higgins, Ph.D. (UCCC 2013)
Higgins cited studies showing that rats fed resistant starch show lower numbers and sizes of lesions due to colorectal cancer, and more cells that express the protein IL-10, which moderates the body's inflammatory response: “Much of this information currently comes from rodent models and small clinical trials but the evidence is encouraging.”
As Higgins says, “… if you let rats get obese, get them to lose the weight, and then feed half of the rats a diet high in resistant starch – these rats don't gain back the weight as fast as rats fed a regular, digestible starch diet. This effect on obesity may help to reduce breast cancer risk as well as having implications for the treatment of colorectal cancer.” (UCCC 2013)
While it's unclear which benefits will prove effective mechanisms of cancer prevention, one thing is clear: resistant starch should be on the menu.
The study was supported in part by the National Institutes of Health.
- Higgins JA, Brown IL. Resistant starch: a promising dietary agent for the prevention/treatment of inflammatory bowel disease and bowel cancer. Curr Opin Gastroenterol. 2013 Mar;29(2):190-4. doi: 10.1097/MOG.0b013e32835b9aa3.
- Jacobasch G, Schmiedl D, Kruschewski M, Schmehl K. Dietary resistant starch and chronic inflammatory bowel diseases. Int J Colorectal Dis. 1999 Nov;14(4-5):201-11. Review.
- Jenkins DJ, Kendall CW, Augustin LS, Mitchell S, Sahye-Pudaruth S, Blanco Mejia S, Chiavaroli L, Mirrahimi A, Ireland C, Bashyam B, Vidgen E, de Souza RJ, Sievenpiper JL, Coveney J, Leiter LA, Josse RG. Effect of legumes as part of a low glycemic index diet on glycemic control and cardiovascular risk factors in type 2 diabetes mellitus: a randomized controlled trial. Arch Intern Med. 2012 Nov 26;172(21):1653-60.
- Johnston KL, Thomas EL, Bell JD, Frost GS, Robertson MD. Resistant starch improves insulin sensitivity in metabolic syndrome. Diabet Med. 2010 Apr;27(4):391-7. doi: 10.1111/j.1464-5491.2010.02923.x.
- Kendall CW, Emam A, Augustin LS, Jenkins DJ. Resistant starches and health. J AOAC Int. 2004 May-Jun;87(3):769-74. Review. Robertson MD. Dietary-resistant starch and glucose metabolism. Curr Opin Clin Nutr Metab Care. 2012 Jul;15(4):362-7. doi: 10.1097/MCO.0b013e3283536931. Review.
- University of Colorado Cancer Center (UCCC). A diet of resistant starch helps the body resist colorectal cancer. February 19, 2013. Accessed at http://www.coloradocancerblogs.org/a-diet-of-resistant-starch-helps-the-body-resist-colorectal-cancer/