Most of the carbohydrates we eat come from starch. If you’ve ever had to watch your blood sugar, the word starch is probably cringeworthy. But did you know there’s actually a good type of starch that may improve your blood sugar and your digestive health? It’s called resistant starch, and it’s not talked about nearly enough.
Resistant starch is resistant to digestion; it travels through your stomach and small intestine still intact and then hits your large intestine where it's fermented and used for food for the friendly bacteria and cells that line your colon.
There are 4 different types of resistant starch:
1. Resists digestion due to being bound to fibrous cell walls. Sources: legumes, grains, and seeds.
2. Starch with a high amylose content, which is indigestible when raw. Cooking these starches makes them digestible, removing the resistant starch. Sources: potatoes, powdered potato starch and unripe bananas. Buy the greenest bananas at the grocery store and try to eat them before they turn yellow. Powdered potato starch can be used as a thickener or just added to foods like yogurt or smoothies as a supplement to get more resistant starch. Just be sure not to use it in a hot recipe (like soup) since heating will remove the resistant starch.
3. Type 1 or type 2 starch that is cooked and then cooled. Raw potatoes may not be palatable to most people, so the best way to get resistant starches from potatoes is to cook potatoes, and then cool them. Cooled potato salad is a great way to get resistant starch from potatoes. Cooked beans that are cooled and then used in a bean salad is another example.
4. Type 4 is a synthetic-type of resistant starch and is generally not recommended over real food resistant starch.
The list of foods high in resistant starch isn’t long, and it takes conscious effort to make sure you’re getting some. There isn’t an official recommended quantity of resistant starch, but research shows benefits in as low as 6 grams per day up to 40 grams per day with some health professionals recommending 15-30 grams a day. According to one study in 2008, Americans are getting only 5 to 8 grams a day. Calculating resistant starch is difficult since it’s not a nutrient that populates on food diary apps and the amount changes depending on the cooking method or ripeness of a food. This link has a list of resistant starch quantities in food.
Impact on Digestion
We’re learning more and more about the importance of our microbiome, or the colony of bacteria that live in our gut. Every person’s microbiome is unique and vital to our health, with hundreds of different bacteria species. Scientists are linking gut health to brain health, weight management, cancer risk and basically every aspect of our health. To grow the number and variety of healthy bacteria in our gut, we need not only probiotics but also prebiotics, which feed the probiotics. Prebiotics come from resistant starch and soluble fiber. When the bacteria feed on resistant starch, they produce several compounds, including short-chained fatty acids like butyrate.
Short-chained fatty acids fuel the cells in your colon. They may reduce your risk of inflammatory diseases, type 2 diabetes and heart disease. SCFAs reduce the pH level of the colon and reduce the risk of colorectal cancer. Butyrate decreases inflammation and decreases intestinal permeability (also known as leaky gut) – therefore keeping toxins in the gut and out of the bloodstream.
Since resistant starches nurture the cells and bacteria in the colon, it has a positive effect on digestive diseases like ulcerative colitis, Crohn's disease, constipation, and diarrhea.
Impact on Blood Sugar
Since resistant starch is not digested in the stomach or small intestine and is instead fermented in the colon to fuel bacteria and cells, it does not raise blood sugar. Multiple studies have shown that increasing resistant starch has a positive impact on post-meal blood sugar and insulin, as well as satiety. Insulin resistance (when insulin can’t do its job of removing blood sugar) is a risk factor for many chronic diseases like type 2 diabetes, metabolic syndrome, and obesity—which further increases the risk for other diseases. One study looking at increased resistant starch showed improvement in insulin resistance in overweight and obese men, but not women. However, another study did show improvement in glucose in both normal weight and overweight women.
Resistant starch has also been shown to improve insulin resistance in people with metabolic syndrome—or people who already have insulin resistance. One very interesting study found that resistant starch even has a “second meal effect” on blood sugar; meaning if you ate a high resistant starch breakfast, not only would that improve your post-meal blood sugar at breakfast, but would also help to control blood sugar after lunch, too.
Oftentimes, weight loss is also seen with improvement in glucose control and insulin sensitivity. Resistant starch has fewer calories than regular starch – 2 calories versus 4 calories per gram – and also leads to satiety. Due to feeling full after eating resistant starch and eating fewer calories, resistant starch may help with weight loss in overweight or obese individuals.
How to Increase Resistant Starch in Your Diet
Take a look at the top food sources of resistant starch listed above and try to incorporate them into your diet daily. The simplest way of increasing resistant starch is to use potato starch as a supplement. Start small and increase as tolerated; one tablespoon is 8 grams. While eating a low carb or moderate carb diet can be very useful for many to control weight and blood sugar, the type of carb you choose makes a major difference. Choosing carbs high in fiber and resistant starch versus regular starch and sugar will make a big impact on your digestion, insulin sensitivity, weight management, and overall health.
Lindsay Nelson, R.D., L.D.
Lindsay Nelson, R.D./L.D., is a freelance dietitian based in Kansas City, Missouri. Most of her time is dedicated to her 3-year-old and 1-year-old boys, teaching them all about cooking, gardening and nature. Her husband and boys are great guinea pigs in the kitchen, always willing to try her latest food creations. On the weekends you’ll usually find them outside on a trail, hanging out with friends and family and always eating good food.