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a person holding oat flakes on their palms
a person holding oat flakes on their palms

Do you know what resistant starch is? Sure, you know it’s a type of starch—the clue is in the name! And you may also know that foods with resistant starch, like white rice, legumes, and green bananas, can have many health benefits. These benefits include better digestive health, a healthy gut, and improved insulin sensitivity for some people. But just in case you don’t already know what starches are, let’s start there. Starches are chains of simple sugars that are linked together. They’re complex carbohydrates, so they’re broken down by your digestive system before the simple sugars can be released into your blood for your cells to use. 

Depending on how quickly your enzymes can ‘liberate’ glucose from their chains, you can categorize starch as rapidly digestible, slowly digestible, and resistant. Here’s a little more about each type:

  • Rapidly digestible starch is digestible in under 20 minutes. You can find high amounts of this type of starch in foods like bread and potatoes.
  • Slowly digestible starch is digestible in 20 to 100 minutes. This will usually have some kink in its structure that makes it more difficult to digest. You can find this in grains like wheat and rice.
  • Resistant starches are the most challenging for the intestine to digest. They remain undigested even after two hours and can be found in many foods like lentils and oats.

Why Should You Care About Resistant Starches?

a person eating oatmeal with berries

Since resistant starches can escape the small intestine, they pass into the large intestine instead of releasing glucose into the blood. The bacteria that live there then digest them. Because these bacteria break down the starch so your body can digest it, they also produce hydrogen, carbon dioxide, methane, and short-chain fatty acids. All this means you may not have as big of a glucose spike when you’re eating resistant starches, because the foods that they’re found in won’t produce as much glucose when you eat them. Resistant starches are also thought to have fewer fermentation products than other molecules digested in the large intestine (like lactulose). 

Some Benefits of Resistant Starches

There may not be a definitive link between resistant starch and blood glucose until there have been large, well-controlled clinical trials. Still, many smaller studies show that resistant starches may improve the way the body handles glucose and insulin when compared to regular starches. Although there’s no conclusive link we can draw here, the studies saw some benefits two to eight hours after a meal. They found that resistant starches have a more significant impact on improving insulin sensitivity and lowering fasting insulin but less on reducing fasting glucose levels. 

Since the bacteria in the large intestine digests resistant starches, they also act as a probiotic that feeds them energy. And they may also have a role in regulating the lipids, like cholesterol or triglycerides, in your blood. They release less energy into your bloodstream, so they may also help when you want to feel full and avoid overeating.

The Side Effects of Eating Resistant Starches

Are there side effects to eating resistant starches? Maybe! Research on the effects of resistant starches is ongoing. Still, a small number of studies that examined resistant starches found that they can enlarge the cecum in some animal models. The cecum is a part of the large intestine that connects the small intestine to the colon. Some people may notice increased gas or bloating related to digestion issues in the large intestine. However, since neither of these findings has been conclusive among humans (and research is still ongoing), it’s best to view this as an interesting tidbit of information for the moment.  

Resistant Starches Among People with Metabolic Syndrome

three sweetcorn on a plate

These types of starches seem to be most effective among people with metabolic syndrome. Metabolic syndrome means that the insulin your body produces doesn't work as well as it should at moving glucose from your blood into your cells. This can increase your risk of all sorts of illnesses and conditions (including type 2 diabetes and heart disease) and is characterized by insulin resistance.

If resistant starches have a more substantial influence on insulin than on glucose, as research suggests, it could potentially help improve the issue. Take the results of this study, for example. Among 20 people with metabolic syndrome, those who took a resistant starch supplement for 12 weeks saw an improvement in insulin sensitivity. However, their overall weight level and blood test inflammatory markers remained unchanged compared to the group that took a placebo.

There are also likely different reactions to resistant starches because of gender, weight, and other lifestyle factors. Let’s look at another example, with a study that evaluated how people react to high-amylose corn. Amylose is a crystallizable form of starch that your body takes longer to digest. The study included 33 generally healthy people of varying ages from 18 to 69, who were overweight or had slightly larger waistlines than average. In the 11 male participants, they saw the most increase in sensitivity to insulin. In contrast, female participants did not see a similar response. This raises the interesting possibility that the effect of resistant starches may be gender-specific, but remember that research is ongoing here too.

an image of natural resistant starch

So, what’s the deal with resistant starches? There’s a lot of ongoing research, but what we do already know is that foods with resistant starch are not specifically harmful in any way for most people. And an intake of resistant starch may even have some health benefits, including an improvement in insulin sensitivity for some. Of course, since there’s no one-size-fits-all when it comes to staying healthy, the only way to tell how it affects your body is to try it out.

Experimenting by adding foods with resistant starch to your diet is a good idea, especially if you have data to back up your food choices. Here’s where a continuous glucose monitor (CGM) can help. Seeing real-time glycemic responses to your dietary choices can be a good way to ensure you're making the right ones for your body.

Want to know more about resistant starch? There’s a lot more to learn, from how similar they are to dietary fibers (like insoluble fiber in particular), to why they function so well as prebiotics. Watch this space for upcoming articles about how resistant starch is made, the four different types of resistant starch, and some of the foods that include them. 

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Kara Collier, RDN, LDN, CNSC

Reviewed by: Kara Collier, RDN, LDN, CNSC

Kara Collier is the co-founder and VP of Health at Nutrisense, one of America’s fastest-growing wellness-tech startups, where she leads the health team. She is a Forbes 30 under 30 recipient, frequent podcast guest & conference speaker.

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