Sunday, April 21, 2024

Chilled Grains and "Resistant Starch"


IRRI Images, CC BY 2.0 , via Wikimedia Commons

"Resistant starch" is in the news.

There is evidence that cooking and then cooling starchy foods (rice, pasta, potatoes, legumes, etc.) transforms some of the starches into "resistant starch". 

Resistant starch is so named because it "resists" breakdown in the stomach and small intestine, instead being broken down by the "good" microbes in the large intestine. It is thus a prebiotic. It is similar in some ways to soluble fiber.

Because it is less digestible, one gram of resistant starch has 2 calories, compared to 4 calories per gram of typical starch or sugar. And resistant starch also takes longer to digest, thus spiking blood sugar less than regular starch.

This is all good news for anyone who is trying to increase their intake of prebiotics, decrease their blood sugar variability, and decrease their calorie intake. Which means that it's good news for an overwhelming majority of people in developed countries, and an increasing number of people in developing countries too.

(continued below…)

This New York Times article talks a lot about this theory, and provides a link to a study abstract in which the "Conclusions" section seems to have been accidentally cut off! And full access to the study costs $28! I have other complaints about this NYT article—in particular that the author and/or editor felt it necessary to recommend high–insoluble fiber foods, despite the fact that the study clearly provides a (small) reason not to prefer these foods.

With some digging, I found the full, unabridged "Conclusions" section of the study abstract, which I reproduce here (I feel like this is "fair use"), with emphasis and numbers added:

RS is found naturally in both processed and whole starchy
foods, including breads, cereals, bananas and plantains,
grains, noodles and pasta, potatoes, rice, and legumes. According
to the database, raw foods, including oats and plantains,
had the highest RS content. Among cooked foods,
potatoes and grains (barley and rice) bred to have a higher
amylose to amylopectin ratio have higher amounts of RS than
those with a lower amylose to amylopectin ratio. [1] Potatoes
and grains that are cooked and then chilled have more RS
than if boiled or heated, where the chilling process promotes
the retrogradation of the starch granule to make it less
The duration of storage also increases RS in some
foods, such as corn tortillas, durum wheat pasta, and black
and pinto beans. [2] Foods with the lowest RS include multigrain
flaked cereal, cooked bananas, cooked unripe plantain chips,
fruit scones, wheat-germ bread, store-bought granola,
cooked corn pasta, and cooked brown rice.

Again, the full article can be found here (for $28).

The two points:

  1. If you cook and then chill your starches, all else being equal, they will be better for you (in the ways described above) than if you eat them hot from their first cooking. (Elsewhere the author indicates that reheating them reduces some but not all of the benefit.) I can think of a lot of typical foods that fall into this category! Pasta salad, noodle salad, rice salad, potato salad. Fried rice, congee, refried beans, and yes, even potato chips! (But please fry your potato chips in saturated fats rather that seed oils. Canola oil is a machine lubricant, not a food.)
  2. The foods in the "low RS" list are higher in insoluble fiber. This makes sense, since more insoluble fiber means less digestible carbs to be transformed into RS.

What are my conclusions?

  • If you are going to eat starches, and if it's convenient to, chill them first!
  • It's hard to say with any kind of consistency the extent of this effect. Moderate at best? Anyone who's really interested can pay the $28 and see what the article has to say about it. (And report back in my comment section if you do!)
  • I feel like this is another (small) reason not to feel any obligation to seek out brown rice, whole-grain pasta, and other high-fiber foods, unless you genuinely like them.

And importantly, I don't think this means we can all eat as much carbs as we want as long as we chill them first. Most of us would do well to decrease carb intake. And folks with diabetes are probably best off avoiding carbs as much as possible.

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