Starch is an efficient way for plants to store glucose, in polysaccharides (sugar chains). There are two main types of polysaccharides: amylose and amylopectin. The former is more of a single chain (so you have to release the glucose molecules one at a time) while the latter is a series of branches (more surface area, so you can release more molecules at once). For that reason, the amylopectin has a higher glycemic index than the amylose. Amylose is therefore the primary type of polysaccharide found in resistant starches.

What Resistant Starch Is

Resistant starch is so called because it is resistant to digestion: it doesn’t get broken down into sugars as readily as other starches. But not all amylose is automatically resistant to digestion—this depends on other factors too, largely dependent on preparation methods, or other chemical reactions. Many resistant starches get broken down with heat, for instance: most whole grains (such as rice and oats) and potatoes are high in resistant starches, but after cooking and when still warm, these starches are no longer resistant. If cooked and allowed to cool, however, the resistant starch properties return.

Unripe bananas are also high in resistant starch–but the ripening process breaks the resistant starch down into very bioavailable sugars, rendering ripe bananas a very high glycemic fruit.

Resistant Starch and Your Gut

Resistant starch is one of the components of fiber, defined as undigestible elements of a plant. Resistant starch specifically acts as a pre-biotic (food for the good bacteria) to the flora in your colon, helping to produce Short Chain Fatty Acids, and primarily butyrate. SCFAs are the food for the colonic cells.  For this reason, 1) resistant starch is great for your digestion, but 2) a sudden extreme increase in resistant starch ingestion may cause gas and bloating (true of any prebiotics your body isn’t used to, as they will act as food for good and bad bacteria alike. If you have any bad bacteria, they will eat it too, and have a party!) This is why it’s a good idea to increase your resistant starches slowly rather than all at once, if you’re not used to eating a lot of whole foods.

Resistant Starch and Your Metabolism

Most of the spotlight surrounding resistant starch lately has involved metabolism. Because resistant starch acts like fiber, slowing the release of carbs into the bloodstream, it has been shown to:

The Upshot

The refined and highly processed carb-dense foods common in the Western world are basically pre-digested. All the resistant starch is gone, which means the calories are ready to be released the second it hits our saliva. It also means we’re starving the good flora in our intestines, which leads to poor digestion.

One great way to increase resistant starch is just to eat a whole food diet—nothing boxed, bagged, canned, or otherwise processed. But you’ll also greatly increase the resistant starch content in your carb-dense foods by allowing them to cool before you consume them (and don’t re-heat either.)

You can also purchase resistant starch supplements such as raw potato starch or hi-maize flour, both of which you can add by the tablespoon to smoothies, yogurt, etc. This is a good choice if you’re otherwise on a low-carb diet, since you’ll add very little digestible carbs to your diet this way.