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Resistant starch is a type of fermentable fiber that’s very beneficial to the human body. It provides food for the good bacteria in the gut, which metabolize it into butyric acid, the main fuel source for colon cells. Without a good supply of butyric acid, the colon cells can’t function optimally, and all sorts of problems (like leaky gut syndrome) can ensue.
You may recall from high school biology (or nutrition) that the two main types of fiber are insoluble and soluble. Resistant starch is kind of a cross between the two. Insoluble fiber doesn’t get broken down but descends into the colon, and moves things along quite effectively, helping to prevent (or treat) constipation, for example. (It was insoluble fiber your grandmother was talking about when she admonished you to “eat your roughage!”
Soluble fiber, on the other hand, absorbs water, and when it gets to the colon, it’s feasted on by the good bacteria in the gut (also known as probiotics). Remember, probiotics are living organisms, and they too have to eat. Soluble fiber – also known as prebiotic fiber – is their perfect food. When they dine on soluble fiber, they create valuable compounds known as short-chain fatty acids (the most important of which is the previously mentioned butyric acid). These short-chain fatty acids serve as fuel for the gut and help keep your microbiome thriving and healthy.
Resistant starch has characteristics of both insoluble and soluble fiber. Much like insoluble fiber, it’s “resistant” to digestion and passes into the colon undigested, but once there, it behaves like soluble fiber and is fermented (digested) by the good bacteria that live there. In fact, you could call it a kind of “super” soluble fiber, producing even more butyric acid than the regular kind of soluble fiber.
Resistant starch is found in foods like Jerusalem artichokes and unripe bananas. It’s also found in raw potatoes and lentils. Interestingly, the resistant-starch content of both cooked potatoes and lentils increases when the foods are cooled.
With the exception of lentils, most foods that contain resistant starch aren’t eaten very frequently. But because resistant starch has such potential for keeping the gut healthy, manufacturers are looking for ways to create resistant-starch supplements (which is why potato starch is becoming a popular supplement).
There are no recommended daily intakes for resistant starch, but there are recommended intakes for fiber in general. Most health organizations recommend between 21 and 38 grams of total fiber a day, depending on your age and sex. (For the record, most Americans get between 10 and 15 grams of fiber a day, the health consequences of which are only now beginning to be appreciated.)