Starches that resist digestion by human digestive enzymes are called resistant starches. They survive the small intestine largely intact and feed the beneficial bacteria residing in the colon.
Resistant starches are found in many plant foods. Good sources include beans and legumes, starchy vegetables, and whole grains. The problem is that the history of agriculture and food processing is largely the tale of eliminating resistant starches. For example, white grains contain only a fraction of the resistant starch found in whole grains. Generations of selective breeding practices have left us with cultivated crops that have significantly less resistant starches than their wild varieties.
And the remaining is wiped out in the kitchen. Cooking oats eliminates 98% of the resistant starches. Even worse, cooked potatoes contain only 0.82% of the resistant starches found in raw potatoes.
In other words, foods that are easy and pleasant for humans to eat contain very little resistant starch.
Consequently, the estimated intake of resistant starches by Americans is only 5 g/day, well short of the recommended 6 g/meal.
Studies show resistant starches produce more butyrate than most other prebiotics. Digestive simulation studies show resistant starches result in a steady production of short-chain fatty acids (SCFA), like butyrate, over 48 hours. On the downside, resistant starches are fermented fairly rapidly. As such people with small intestine bacterial overgrowth should be careful with them, and they aren’t suitable during the first phase of the gut healing protocol.
Not all RS is created equal
There are four types of resistant starches:
- Type 1 is found in grains, seeds, and legumes and resists digestion because it is bound within the fibrous cell walls.
- Type 2 is found in some starchy foods, including raw potatoes and green (unripe) bananas.
- Type 3, so-called retrograde RS, is formed when certain starchy foods, including potatoes and rice, are cooked and then cooled. The cooling turns some of the digestible starches into resistant starches via a process called retrogradation.
- Type 4 is man-made and formed via a chemical process (doesn’t mean it’s unhealthy).
The easiest, but not recommended, way to get resistant starch is to consume potato starch, plantain flour, or green banana flour. All are excellent sources of type 2 RS. I do not recommend you take these.
The mistake many people make is to consume large amounts of potato starch (or another type 2 RS) and leave it at that. That can reduce the microbial diversity in the gut as type 2 RS is a more selective feeder. Meaning that fewer bacteria can ferment it than type 3 RS. Consuming large quantities of type 2 RS encourages the growth of the bacteria that can ferment it. Over time, they crowd out other bacteria from the gut. The problem is that many of the bacteria getting crowded out are essential for a healthy gut.
Another issue is that RS2 ferments rapidly. There’s a concern that consuming potato or banana starch encourages bacteria to migrate up to the small intestine.
The science on this is anything but settled yet, but Dr. Grace Liu makes a compelling argument against too much type 2 RS on her blog.
My recommendation is to get RS3 starch from foods. Here are some tips for doing that:
- Eat some starchy vegetables, legumes, and nuts and seeds. Legumes are better soaked for 12 to 24 hours before cooking to remove the anti-nutrients and improve digestibility.
- Whole grain rice and corn are also good sources of RS.
- For starches, grains and legumes, cook first and allow to cool before eating to increase retrograde RS content. Freshly cooked, these foods have little to no RS. Ideally, store for 24 hours in the fridge before eating. You might want to cook them in larger batches, store in the fridge, and eat as needed. Reheating in the microwave is OK. Reheating somewhat reduces the amount of RS3, but I suspect that in the big picture it doesn’t matter.
For more details on the resistant starch content of various foods, please see this PDF from FreeTheAnimal.com.
Given what we’ve talked about the role of fermentable fiber in gut issues, I don’t recommend you go overboard with resistant starches. Eating too much of any fermentable carbohydrates may lead to problems. Aim to include RS3-rich foods into one meal a day. Examples of foods with RS 3:
- Potato salad (made from cooked and cooled potatoes)
- Sushi rice
- ‘Glass noodles’ – translucent noodles
Good articles on resistant starch