Monday, February 02, 2009

Blood Sugar Problems? Go For The Starch: Resistant Starch

More on how carbohydrates help manage blood sugar, diabetes, and obesity.

Diets high in carbohydrates, specifically the high-fiber, slow-digesting, fermentable kind, have been shown in several studies to improve blood glucose and cholesterol levels, decrease insulin resistance (a good thing), and help control weight. (Here's one study.)

One way they're thought to do this is by increasing the number of receptors for insulin, and improving how insulin binds to its receptor. (More good things.)

This study describes an additional mechanism. It involves a specific kind of carbohydrate: resistant starch. (I've written about resistant starch, what it is and what foods contain it, on these posts.) Simply, resistant starch is starch (carbohydrate) that resists digestion in the small intestine and ends up in the colon where bacteria feed on it, producing an array of chemicals including some called short chain fatty acids (SCFAs).

In this study, those SCFAs were found to increase the amounts of two hormones that are produced and released from the cells of our gut: 1
  • Glucagon-like peptide-1 (GLP-1)
  • Peptide YY (PYY)
These hormones reduce appetite (increase satiety) and slow gastric emptying (slower digestion means slower and lower post-meal glucose spikes), among other actions.

Study findings:
  1. RS stimulates GLP-1 and PYY secretion in a substantial day-long manner, independent of meal effect or changes in dietary glycemia.
  2. Fermentation and the liberation of SCFAs in the lower gut are associated with increased proglucagon and PYY gene expression.
  3. Glucose tolerance, an indicator of increased active forms of GLP-1 and PYY, was improved in RS-fed diabetic mice.
Take note of finding #1. These hormones typically degrade rapidly after we eat. That wasn't the case here. Higher levels were found for up to a day after resistant starch was consumed.

This helps to explain the "second meal effect," which I talked about here:
"The foods we eat hours and up to a day after a meal that produces SCFAs, even if those subsequent meals contain a lot of easily digestible (high GI) carbohydrate, will be digested more slowly, and the glucose that enters the bloodstream afterwards will be cleared faster."
Good sources for resistant starch? Cooled cooked potato, cooled cooked pasta (cooling rearranges starch structure making it more difficult to digest), starchy beans e.g. kidney beans, and unripe bananas - the green ones.
1 Dietary Resistant Starch Upregulates Total GLP-1 And PYY In A Sustained Day-Long Manner Through Fermentation In Rodents, American Journal of Physiology: Endocrinology and Metabolism, November 2008.

1 comment:

Anonymous said...

This is excellent information. More MDs and dietitians need to be schooled in this.