Eating leftovers is a great way to reduce food waste and save money, but have you ever heard that certain foods are healthier after being cooled and reheated? Pasta, rice, potatoes,and other starchy foods might be better for you the next day, according to a health hack going viral on social media.
While it may sound too good to be true, there is some science to explain why leftover carbs may be healthier. It all has to do with something called resistant starches, which are transformed by the cooking and cooling process.
As a result, the starches in carbohydrate-heavy foods are harder to digest, acting like a fiber that slows down the absorption of blood sugar, so the body doesn’t take in as many carbs. Here’s what to know about this health hack and how it may affect nutrition goals:
What are resistant starches?
Starch is a complex carbohydrate found in many plant foods, which consists of glucose molecules bonded together. These are broken down by the digestive system into accessible energy (glucose) that fuels the body, Dr. Vijaya Surampudi, chief of the division of clinical nutrition at UCLA Health, tells TODAY.com.
Resistant starches, on the other hand, are a type of carbohydrate that, due to their molecular structure, resists digestion until they get to the colon or large intestine, where they are fermented by gut bacteria, Razan Hallak, a registered dietitian at the Ohio State University Wexner Medical Center, tells TODAY.com.
There are multiple types of resistant starch. It is found naturally in many plant foods including whole grains, legumes, seeds, raw potatoes and unripe bananas, says Hallak. Resistant starch can also be produced in starchy foods like pasta, potatoes and white rice through cooking and cooling.
Resistant starch benefits
Resistant starch is thought to have many health benefits. First, it acts like a prebiotic dietary fiber by feeding the bacteria in our colon, which promotes a healthy gut microbiome, the experts note. These bacteria ferment the resistant starch, turning it into short-chain fatty acids, which may have anti-inflammatory, cardiovascular and protective benefits.
Additionally, resistant starch slows down the absorption of glucose into the bloodstream, so it does not spike blood sugar as much as other starches, says Surampudi. This may also help with insulin resistance and feelings of satiety, or fullness.
There is research suggesting that resistant starches may help lower the risk of colorectal cancer in certain people.
Resistant starch is also thought to help with weight management. “Some research has shown that it could affect weight loss, in theory,” says Hallak.
How does cooling increase resistant starch?
Cooking food normally destroys resistant starches. Freshly cooked, hot starchy foods have a looser structure of glucose molecules, which can be digested readily by the body and raise blood sugar.
Cooling these foods can allow the resistant starches to reform by tightening up the molecular bonds. “When you cool it down, the molecules rearrange themselves into a more crystallized (tighter) structure … able to resist digestion in the small intestine,” says Surampudi. This process is called called retrogradation.
The longer you cool the starchy food, the more retrogradation occurs, Surampudi says. Generally, it’s recommended to cool the pasta or rice for at least 24 hours in the refrigerator, set to 40 degrees Farhenheit or below.
A 2015 study published in the Asia Pacific Journal of Clinical Nutrition, showed that cooked white rice that had been cooled for 24 hours then reheated had about two and a half times more resistant starch than the freshly cooked rice.
Reheating cooled starchy foods is not thought to change the molecular structure again, says Surampudi. The reformed resistant starch is more heat-resistant, “so reheating it does not usually destroy it,” Darrell Cockburn, Ph.D., associate professor of food science at Penn State University, previously TODAY.com.
Do leftover pasta and other carbs have fewer calories?
Cooked and cooled pasta, potatoes, or rice will have more resistant starch, which acts as a fiber and is not readily digested. In addition to not spiking your blood sugar as much, the body will absorb fewer carbohydrates and calories, Surampudi notes.
The extent to which cooling these foods will lower carbohydrate and calorie absorption is less clear, the experts say. It’s likely a very modest amount. Additionally, research suggests the effect of chilling and reheating starchy foods on blood sugar levels varies between rice, pasta and potatoes.
A 2022 study published in the journal Nutrition & Diabetes showed that 100 grams cooled rice has about 5 fewer grams of digestible carbs compared to the same portion of freshly cooked rice. Other research shows cooking and cooling white rice may reduce calorie absorption by about 10-15%, TODAY.com previously reported.
In a 2019 study published in the journal Foods, researchers found that subjects who ate cooled and reheated pasta returned to fasting blood glucose levels faster than those who ate freshly cooked pasta.
In contrast, previous studies have shown pre-cooked and chilled potatoes lowered the glycemic response, but the same effect was not observed with cooled and reheated potatoes.
“There are so many different factors, and we just don’t have enough information,” says Hallak. “If you don’t know how much you’re lowering your carbs, you’re not going to be able to tell how it’s going to affect you,” she adds.
Are leftover pasta and other carbs healthier?
Cooked and cooled pasta, potatoes, white rice and other starchy foods could potentially be healthier, mainly due to their higher resistant starch content. This type of fiber feeds good bacteria in the gut and doesn’t spike blood sugar as quickly.
Most people can benefit from increasing the amount of resistant starch, and fiber in general, in their diets.
However, cooling and reheating carbs — and its effect on glycemic response — may be especially helpful for people who need to watch their blood sugar levels, such as those with Type 2, TODAY.com previously reported.
Leftover starchy foods may have slightly less available carbohydrates and calories, but more research is needed to make claims about weight loss. “If (this hack) is affecting anything, it’s a very trace benefit,” says Hallak. Reducing your carb intake (by limiting portion size, for example) will likely yield better results, she adds.
“It’s hard to give a general recommendation that you need to eat your starches as leftovers, (but) maybe in the future, if we have more research,” says Hallak.
Freshly cooked pasta, rice or potatoes can also be healthy when eaten in moderation as part of a balanced diet.
While leftover pasta, rice and other starchy foods may be slightly better for you, the experts agree that it’s also important to mix in carbs naturally high in resistant starches. These include whole grains like oats and barley, legumes like lentils and beans, and starchy vegetables such as plantain or green bananas.
Additionally, Hallak recommends balancing starchy foods with lean protein sources and other nutrient-dense plant foods to get more benefits.
If you want to try this hack, make sure you cool and store your leftovers properly to reduce the risk of food poisoning. Certain bacteria can thrive in starchy foods and multiply rapidly when these are left out at room temperature. Always refrigerate cooked food within two hours and put it in small containers to cool faster.
Always reheat leftovers until they reach an internal temperature of 165 degrees Fahrenheit, per the USDA. After about three or four days, you should toss your leftovers out.
This article was originally published on TODAY.com