Retrogradation is a process in which food starches, after cooking and cooling, crystallize to become resistant to digestion. The conversion reduces the digestible calories and increases health benefits.

How Does This Happen?

Starches are long molecules of glucose chains, either linear (amylose) or branched (amylopectin). Cooking alters the plant foods with these structures increasing digestibility and safety.

For example, some starchy uncooked foods like potatoes, beans, and eggplant contain harmful compounds that cooking destroys.

Additionally, before cooking, plant starches can be difficult for digestive enzymes to access due to the plant’s physical structure and strong hydrogen bonds that hold the starch molecules together in a dense, granular form.

However, cooking, particularly in water, breaks these barriers and allows hydrogen bonds to form between the starch and water molecules, improving digestibility and giving the starch/water complex a gel-like as opposed to granular texture.

But cooling the foods after cooking them, allows starch molecules to realign into tightly packed crystalline structures, called retrograded starch. Retrograded starch resists digestion in the small intestine and is instead fermented by beneficial gut bacteria in the large intestine. While retrogradation is generally considered beneficial to health, it is responsible for the staling of bread.

What Foods Does This Include

Although most starchy foods are subject to retrogradation, foods higher in amylopectin and lower in amylose (waxy starches) and those cooked with added fats, dairy, or egg are less so.

The amylose in foods tends to crystallize faster than amylopectin. Although differing lengths of amylose and food source can affect the rate, amylose generally takes three hours of cooling after cooking to reach its maximum quantity of retrograded starch, whereas amylopectin starches take approximately 12 hours.

While most plant foods have both forms of starch, examples of foods subject to high retrogradation include corn, legumes, chickpeas, barley, brown rice, basmati rice, wheat, pearl millet, sorghum, quinoa, and plantains. However, short grain rice and waxy corn are considered to have more amylopectin and tend to retrograde less.

Does Reheating Reverse Retrogradation?

Foods higher in amylose retain their resistant nature more than those higher in amylopectin.

While extremely high heat or prolonged cooking may slightly reduce resistant starch levels, typical reheating methods such as microwaving or gently reheating on the stove do not significantly reverse retrogradation.

Improving Fiber Content

Retrograded starch is one of five forms of resistant starches (RSs), which are considered dietary fiber. The RS from retrogradation is identified as RS3. The others are RS1 which are in whole grains, seeds, and legumes, RS2 from potatoes and green bananas, RS4 from industrialized processes that alter food texture, and RS5, amylose-lipid complexes, that form when starches are cooked with added fats and oils.

Acting like soluble fiber, retrograded starch reduces blood sugar spikes, reduces blood cholesterol, and feeds beneficial gut microbes.

Calorie Reduction

And because RS3 is an indigestible fiber, the food’s caloric content decreases too. For example, cooling cooked rice can reduce available calories by 50%; cooked and cooled potatoes may have 40% less available calories; and pasta, even after cooking, cooling, and reheating, retains only 30% of its original calories.

Summary and Conclusion

Retrogradation occurs after starchy foods such as rice, legumes, barley, and quinoa are cooked and then cooled. Being converted from digestible to indigestible starch that acts as insoluble fiber, retrograded starch reduces calorie absorption, supporting weight management, improves blood sugar responses, and promotes gut and metabolic health.

About the Author

Patrick Traynor, PHD, MPH, RD, CPT is a registered dietitian with an insurance-based practice, MNT Scientific, LLC in South Lake Tahoe, CA, Minden, NV, & Ashland, OR. In office or video appointments can be requested online at MNTScientific.com or by calling (530)429-7363. Inquiries can be directed to info@mntscientific.com.