You likely eat resistant starches every day, but do you understand what they are and why they’re important to your overall health?  

Resistant starches are unlike other carbohydrates in your diet. They’re a type of fiber found in carbohydrate-rich foods that the body can’t absorb in your digestive system. Instead, they pass from the small intestine into the large intestine, remaining undigested. It’s here, through fermentation, that resistant starch is changed into short-chain fatty acids — where it helps to feed your healthy gut bacteria. 

Resistant starches are found in various whole foods, such as starchy vegetables, bananas, beans, nuts, and seeds. Depending on how foods are prepared, resistant starch can help to lower its glycemic index. You can simply cook and cool rice, pasta, and potatoes for this effect.

Research suggests resistant dietary starches may have positive health benefits, including improvements in insulin sensitivity, glucose time in range, and even digestion. Exactly how this happens isn’t clear, but some evidence suggests it’s through changes to healthy gut bacteria (microbiota).  

 

Types of resistant starch 

Resistant starches are classified into five types — all of which are touted to support metabolic health. The following classification system highlights the various types of resistant starches. Keep in mind that more than one source can be found in the same food.  

Type 1 resistant starches are physically protected from being digested by hard shells. Sources include whole or partially milled seeds, grains, beans, peas, and lentils. 

Type 2 resistant starches are protected from digestive enzymes, so they cannot be digested. Sources include raw potatoes, some legumes, unripe (green) bananas, and corn.  

Type 3 resistant starches are physically modified through the cooking and cooling process. Sources include bread, tortilla, cooked and cooled potatoes, rice, and pasta.  

Type 4 resistant starches are synthetic starches created to be resistant to digestive enzymes. They’re usually found in cereals. 

Type 5 resistant starches are newly discovered and are starches combined with a fat, making them more digestive-resistant. 

 

Why is resistant starch good for digestive health?  

Again, when consumed, resistant starches ferment in the large intestine. This process changes resistant starch into a short-chain fatty acid called butyrate. 

This process is thought to positively impact digestive health by creating more good bacteria and boosting gut health. This can be especially important if you live with a digestive condition.   

Research on butyrate is ongoing, but it is thought to be a prebiotic which feeds the microbiota. It’s also a preferable energy source for the digestive tract and microbiota cells. 

 

How do resistant starches affect glucose levels? Here’s my answer 

Resistant starches may be helpful for people living with diabetes or those at risk of developing it. Further research is needed, and not all findings agree with this. It’s also thought that including resistant starches in meals may help reduce after-meal glucose elevations.  

That said, as a dietitian and person living with T1D, I couldn’t resist testing how resistant starches would impact my glucose levels. I’m always looking for tools to make this balancing act somewhat easier. I’ve previously worked on pre-bolus timing, exercise routines, carb-to-insulin ratios, and different ways of eating.  

I started with rice because it’s one of my favorite foods, but it has always been difficult for me to dose insulin for. If you live with diabetes, you can likely relate. Plus, there is research on the cooling of rice and its effects on post-meal glucose levels in type 1 diabetes.  

My personal experience with eating cooled and reheated rice was a win — in that I did not experience the after-meal glucose spike that I typically do when eating cooked rice.  

 

How do I incorporate resistant starches into my diet? 

As a dietitian, I always encourage my clients to incorporate fiber into their diet to help manage glucose levels. Since my experiment, I’ve been encouraging increased resistant starches, too.  

It’s important to have a “slow and steady” approach, as fiber can cause some uncomfortable symptoms such as gas, pain, bloating, or cramping.  By taking your time and working up to the recommended 15 grams per day, you can usually avoid side effects while gleaning other health benefits.  

Now that you understand more about resistant starches, you may be interested in adding them to your diet. Let’s look at best practices for preparing potatoes. 

In general, research suggests that chilled potatoes can make it more difficult to break down carbohydrates, which slows down digestion. However, results may be different for different people. You can see if it makes a difference for you in terms of post-meal glucose levels — similar to what I did with rice. 

Try cooking (steaming or boiling) and cooling or freezing potatoes before eating them to increase their fiber (resistant starch) content. Making cold potato salad, rather than having oven roasted potatoes is a great substitution.   

 

What’s the bottom line? 

The benefits of resistant starches may go well beyond digestive health. Research suggests promising connections between dietary resistant starches and improvements in glucose time in range, gut microbiome, inflammation, and body structure for those living with overweight or obesity. By incorporating resistant starches in your diet, you may notice some of these potential health benefits.