What is Resistant Starch and Why Does It Matter?
Resistant starch is a type of carbohydrate that, as its name implies, resists digestion in the small intestine. Instead of being broken down into glucose, it travels to the large intestine where it is fermented by beneficial gut bacteria. This process produces short-chain fatty acids (SCFAs), such as butyrate, which fuel the cells lining the gut and support a healthy gut microbiome. A healthy gut has been linked to numerous benefits, including improved blood sugar control, better digestive function, and even reduced inflammation.
There are several types of resistant starch, with two being particularly relevant to oats. Raw, unprocessed oats contain a type of resistant starch known as RS2. However, cooking can significantly reduce this type of resistant starch. The good news is that cooking and then cooling starchy foods like oats can create a new type of resistant starch, called RS3, through a process known as retrogradation. The amylose molecules in the starch re-crystallize as the food cools, making them less accessible to digestive enzymes.
The Difference Between Steel Cut and Rolled Oats
To understand their resistant starch potential, it's helpful to know how steel cut and rolled oats are processed differently. Both start as oat groats, which are the hulled whole-oat kernels.
- Steel Cut Oats: Also called Irish or coarse oats, these are simply oat groats that have been chopped into two or three pieces with steel blades. This minimal processing leaves the oat's structure largely intact, which means it takes longer to cook and has a chewier, heartier texture.
- Rolled Oats: Often called old-fashioned oats, these are steamed and then rolled flat. This process changes their structure, allowing them to absorb water faster and cook more quickly.
The difference in processing impacts their glycemic index (GI), a measure of how quickly a food raises blood sugar. Because of their more intact structure, steel cut oats take longer to digest and have a slightly lower GI than rolled oats. This can be a benefit for managing blood sugar levels.
Comparing Resistant Starch: Steel Cut vs. Rolled
When it comes to cooked oatmeal, the truth is that the method of preparation is far more important than the type of oat for maximizing resistant starch. A study found that cooking significantly decreased resistant starch in oats. However, allowing the cooked oats to cool overnight, a process that creates RS3, can increase resistant starch levels significantly in both varieties. The effect is likely similar for both steel cut and rolled oats, as the crucial factor is the retrogradation that occurs upon cooling.
Here’s a breakdown comparing the two types of oats, considering their preparation and resistant starch content:
| Feature | Steel Cut Oats | Rolled Oats |
|---|---|---|
| Processing | Minimally processed (chopped) | More processed (steamed and flattened) |
| Cook Time | Longer (15-30 minutes) | Shorter (5-10 minutes) |
| Texture | Chewy, hearty, less mushy | Softer, creamier, more consistent |
| Glycemic Index | Slightly lower | Slightly higher |
| Resistant Starch (Raw) | Contains Type 2 resistant starch | Contains Type 2 resistant starch |
| Resistant Starch (Cooked) | Cooking reduces RS | Cooking reduces RS |
| Resistant Starch (Cooked & Cooled) | Contains higher levels of retrograded RS3 | Contains higher levels of retrograded RS3 |
How to Maximize Resistant Starch in Your Oats
To get the most resistant starch from your breakfast, focus on the cooking and storage process. Here are some strategies:
- Make overnight oats: This method of soaking raw oats in liquid overnight (instead of cooking with heat) retains more of the natural resistant starch. This also creates a new type of resistant starch as the oats absorb the liquid and cool down.
- Cook and cool: Prepare your oatmeal as you normally would, then refrigerate it overnight. As the cooked oats cool, the starches undergo retrogradation, increasing their resistant starch content. Reheating them the next day won't destroy the newly formed RS3.
- Use chilled oats in smoothies: Adding raw or pre-cooked and cooled oats to a smoothie is an easy way to incorporate resistant starch without heating it.
- Add other resistant starch sources: Combine your oats with other foods high in resistant starch, like cooked and cooled lentils, chickpeas, or a spoonful of raw potato starch.
The Final Word: It's All in the Preparation
While steel cut oats have a slight nutritional advantage due to their minimal processing and lower glycemic index, the idea that they inherently possess significantly more resistant starch than rolled oats is a misconception when both are cooked normally. The real power to increase this beneficial prebiotic fiber lies in the preparation method, specifically in utilizing the cooling process to create resistant starch through retrogradation. For maximum gut health benefits, the best practice is to cook your oats and let them cool, or simply make overnight oats. Both steel cut and rolled oats can provide a valuable source of fiber and resistant starch when prepared correctly, making either a healthy choice.
For more information on resistant starch and its benefits for gut health, refer to the narrative review from the National Institutes of Health.
Conclusion
Ultimately, the choice between steel cut and rolled oats depends on your preference for texture and cooking time, as their potential for resistant starch is maximized by the same cold storage technique. For optimal gut health, incorporating either type into a cook-and-cool routine or making overnight oats is the most effective approach to boosting resistant starch levels. This focus on preparation, rather than just the oat variety, is the key takeaway for anyone seeking to improve their diet with this powerful prebiotic fiber.
