Resistant starch, a type of carbohydrate, has gained increasing attention as a valuable dietary fiber. Many people are interested in incorporating it into their eating habits due to its various health benefits. A common question arises once resistant starch is formed in food: what happens to this beneficial compound when the food is subsequently reheated?
Understanding Resistant Starch
Resistant starch is a unique carbohydrate that escapes digestion in the small intestine, reaching the large intestine where it undergoes fermentation by gut bacteria. This resistance to digestion gives it properties similar to dietary fiber. There are several classifications of resistant starch based on its structure and origin.
Type 1 resistant starch (RS1) is physically inaccessible, often found encased within the fibrous cell walls of whole grains, seeds, and legumes. Type 2 (RS2) exists in its native, raw form, such as in green bananas and uncooked potatoes, where its compact structure makes it difficult for enzymes to break down. Type 3 (RS3), known as retrograded starch, forms when starchy foods are cooked and then cooled, a process called retrogradation. During cooking, starch granules absorb water and swell (gelatinization); upon cooling, the starch molecules, particularly amylose, reassociate into crystalline structures that resist digestion. Foods like cooked and cooled rice, potatoes, and pasta are notable sources of RS3.
The Impact of Reheating
The question of whether reheating destroys resistant starch is a central concern for many. While some resistant starch, particularly RS3 formed through retrogradation, can experience partial changes upon reheating, it generally does not lead to complete destruction. Research indicates that foods initially cooked and cooled still retain higher levels of resistant starch after reheating compared to their freshly cooked counterparts. For instance, white rice that was cooked, refrigerated for 24 hours, and then reheated showed 2.5 times more resistant starch than freshly cooked rice.
The extent of resistant starch retention during reheating can vary depending on several factors. Reheating can disrupt the crystalline structure formed during retrogradation, particularly affecting the less heat-stable amylopectin component more than amylose. However, the more thermostable amylose-rich structures tend to persist. Specific food types also play a role.
Studies have suggested that certain reheating methods, such as microwave reheating of rice, can actually increase resistant starch content and reduce digestible starch fractions. Reheating pasta that has been cooked and cooled can further enhance the resistant starch effect, contributing to a lower blood sugar response. This indicates that while some structural changes occur, a substantial amount of beneficial resistant starch typically remains available.
Maximizing Resistant Starch Retention
Preserving resistant starch when reheating food involves adopting specific strategies. The initial cooking and cooling process is fundamental for the formation of RS3. For foods like rice, potatoes, and pasta, cooking them thoroughly and then refrigerating them for at least 12 to 24 hours allows for optimal retrogradation. For pasta, cooking it al dente before cooling can further support resistant starch formation.
When reheating, gentler methods are often recommended to help maintain the integrity of the resistant starch. Steaming or carefully microwaving foods can be more beneficial than using very high, dry heat. Reheating only until the food is warm, rather than piping hot, can also minimize potential structural changes.
Adding a small amount of moisture during reheating can contribute to a more favorable environment for resistant starch retention, preventing excessive drying that might compromise the starch structure. While reheating does not destroy all resistant starch, consuming some cooled foods, such as in a potato or pasta salad, ensures maximum retention.
Why Resistant Starch is Valued
Resistant starch provides several health benefits that make its retention in food desirable. It functions as a prebiotic, serving as nourishment for beneficial bacteria residing in the large intestine. As these gut bacteria ferment resistant starch, they produce short-chain fatty acids (SCFAs), with butyrate being a particularly important one that provides fuel for the cells lining the colon.
Beyond its role in gut health, resistant starch can contribute to improved blood sugar control by moderating post-meal glucose spikes and enhancing insulin sensitivity. It also aids in digestive health, potentially alleviating issues like constipation and reducing inflammation within the gut. Resistant starch promotes feelings of fullness, which can support weight management efforts.