Understanding Resistant Starch
Resistant starch (RS) is a type of starch that bypasses digestion in the small intestine and instead ferments in the large intestine. It behaves more like a soluble, fermentable fiber, and its fermentation process creates beneficial short-chain fatty acids (SCFAs) like butyrate, which nourishes colon cells. There are different types of resistant starch, with Type 3 (RS3) being the most relevant for cooked and cooled beans, formed by the retrogradation of gelatinized starch.
Beans with High Resistant Starch Content
While most legumes contain some level of resistant starch, specific types consistently show higher concentrations, especially after being properly cooked and cooled. The variability in measured resistant starch can be significant due to differences in analytical methods, bean cultivar, and preparation. However, a consensus highlights several top contenders:
- Kidney Beans: These are a standout source, with one study indicating that their starch was between 70.9% and 83.1% resistant. The higher amylose content in kidney beans contributes to this effect, making them particularly favorable for glycemic control.
- White Beans (Cannellini, Navy): White beans, including navy beans, are often cited for their high resistant starch content. Research suggests they can contain substantial amounts of RS, although figures can vary significantly between sources. Navy beans, in particular, are known for a high concentration of resistant starch that ferments slowly, which can minimize gas and bloating.
- Pinto Beans: Studies have shown that pinto beans are also an excellent source of resistant starch, especially after cooling. In one evaluation, cooked pinto beans had higher levels of resistant starch than cooked black beans after one hour. A 24-hour cooling period further increased their RS content.
- Black Beans: Black beans are a very good source of resistant starch, offering a percentage of RS comparable to pinto beans after cooking and cooling. They are known for supporting gut health and regulating blood sugar.
- Lentils and Chickpeas: These also provide resistant starch, although typically in slightly lower quantities than the top-tier beans, especially after standard cooking. However, cooking followed by cooling is still an effective way to increase their RS levels.
The Role of Cooking and Cooling
The method of preparation plays a crucial role in determining the final resistant starch content. Cooking starch-rich foods like beans causes the starch granules to absorb water and swell in a process called gelatinization. When these foods are cooled, the starch molecules, particularly amylose, can re-associate and crystallize, forming resistant starch through a process called retrogradation (RS3). This makes cooked and cooled beans more beneficial than freshly cooked ones. Refrigerating cooked beans for 24 hours can significantly increase their resistant starch content.
- For maximum resistant starch:
- Cook beans thoroughly until tender.
- Cool them completely, preferably in the refrigerator for at least 24 hours.
- Reheat if desired. Reheating does not significantly reduce the retrograded resistant starch.
- Try adding beans to cold salads or using them in chilled spreads like hummus to preserve the highest levels of RS.
Comparison of Bean Resistant Starch Potential
This table illustrates how resistant starch levels can vary by bean type and preparation, based on available research. Note that these are estimates, as measurement methods differ.
| Bean Type | Resistant Starch (Cooked) | Resistant Starch (Cooked & Cooled) | Key Characteristics |
|---|---|---|---|
| Kidney Beans | High (~32% of dry weight) | Very High (up to 83% of total starch) | High amylose content, excellent for blood sugar control. |
| Navy Beans | High | Very High | Particularly rich in RS, slow-fermenting, and helps reduce gas. |
| White Beans | High | Very High | Great source of fiber and resistant starch, with content sensitive to preparation. |
| Pinto Beans | Medium-High | High (increases significantly after cooling) | Good source, with RS levels comparable to black beans and boosted by chilling. |
| Black Beans | Medium-High | High (increases after cooling) | Supports gut health and provides sustained energy. |
| Chickpeas | Low-Medium | Medium-High (increases with cooling) | Lower initial RS in raw form, benefits from cooling after boiling. |
| Lentils | Low-Medium | Medium-High (increases significantly with cooling) | Excellent source of protein and fiber, with RS increasing after cooling. |
Health Benefits of Resistant Starch
The benefits of consuming resistant starch go beyond just improved digestion and are linked to several aspects of metabolic health:
- Enhanced Gut Health: Resistant starch serves as a prebiotic, nourishing the beneficial bacteria in your gut. These microbes ferment the RS into SCFAs, which support a healthy gut microbiome.
- Blood Sugar Control: Because resistant starch is not digested in the small intestine, it does not cause a spike in blood sugar. This can increase the body's sensitivity to insulin and help regulate blood glucose levels, benefiting those with or at risk for type 2 diabetes.
- Increased Satiety: The fiber and resistant starch in beans help promote a feeling of fullness, which can support weight management by naturally reducing calorie intake.
- Reduced Inflammation: Some SCFAs produced during fermentation, like propionate, have been shown to have anti-inflammatory effects.
Conclusion
While all legumes are a healthy addition to any diet, focusing on certain types and preparation methods can significantly boost your intake of resistant starch. Kidney, navy, and white beans are among the top sources, especially when prepared by cooking and cooling. Implementing simple strategies, such as refrigerating a batch of cooked beans before use, allows you to maximize the prebiotic benefits of these pantry staples. By choosing beans rich in this special type of starch, you can actively support your gut health, manage blood sugar levels, and enjoy the many nutritional advantages legumes have to offer.
For more information on the science behind resistant starch, consider reading the Resistant starch facts from CSIRO.
