There is a rumor circulating online that “freezing bread is good for your health.”
Some people may think that this information sounds fake, but in fact there is solid evidence that its effects have been reported in past studies.
According to research, this effect occurs when the viscous starch produced during baking of bread is transformed into “resistant starch,” which is less easily digested and absorbed when frozen.
This resistant starch not only prevents a sudden rise in blood sugar levels, but is also expected to have the effect of regulating intestinal flora.
It is said that the effect of this starch can also be seen when rice is frozen.
Let’s take a closer look at how it works and its health benefits.
What are the downsides of “starch” in freshly baked bread?
Let’s first look at the properties of the starch contained in freshly baked bread.
When bread is baked, the moist dough transforms into fluffy bread, but at this time, the starch molecules in the flour lose their order due to heat and moisture and turn into sticky starch .
This phenomenon in which starch becomes viscous and pasty when heated with water is called “gelatinization” or “gelatinization.”
Gelatinization also occurs when white rice is cooked or when flour is added to a sauce to thicken it.
Therefore, when you cook rice in a rice cooker, it becomes sticky and sticks together, but this is because the starch has gelatinized.
Gelatinized starch is easily digested in the small intestine and quickly absorbed into the body, providing the body with energy. However, it also makes it easier for the glucose (sugar) contained in the starch to be absorbed into cells.
When a large amount of glucose is absorbed, a sudden rise in blood sugar levels occurs, known as a “blood sugar spike.”
When blood sugar levels rise sharply, harmful reactive oxygen species are produced, which begin to damage blood vessels. When the blood vessels try to repair the damage, their inner walls become thicker and harder, making them more susceptible to clogging.
This causes arteriosclerosis to progress and increases the risk of myocardial infarction and cerebral infarction.
In response to a sudden rise in blood sugar levels, excess insulin is secreted to lower blood sugar levels.
Insulin has the function of converting sugar in the blood into fat and storing it in the body, but excessive secretion of insulin accelerates this process, making you more susceptible to obesity .
By the way, excessive insulin secretion causes a sudden drop in blood sugar levels , which can lead to hypoglycemia and cause extreme drowsiness after eating. This is said to be the principle behind the “binge eating fainting” phenomenon that is a hot topic on the Internet.
Freezing food makes starch less digestible and absorbable!
However, when this gelatinized starch is cooled, the glucose strings that were stretched by heating re-entangle, forming many knots, and the starch begins to shrink and become difficult to digest.
This is the type of starch that is difficult to digest, called “resistant starch.”
Although resistant starch is a carbohydrate, it cannot be broken down by enzymes in the digestive tract, making the sugar less easily absorbed by the body.
This allows resistant starch not only to prevent a sudden rise in blood sugar levels , but also to function in the same way as dietary fiber .
Carbohydrates, lipids, and proteins are digested in the body and absorbed by the small intestine, but dietary fiber is a component that cannot be broken down by the body’s digestive enzymes.
Therefore, it bypasses the small intestine and reaches the large intestine, where it serves as food for intestinal bacteria , exerting a “intestinal regulating effect” that regulates the intestinal environment.
It is known that cooling bread actually converts the gelatinized starch into resistant starch, which is less likely to be digested.
In particular, freezing bread produces about twice as much resistant starch as refrigerating it.
So, what exactly are the health benefits of freezing bread and rice?
Health benefits of freezing bread
A study by Oxford Brookes University (OBU) in the UK examined the health benefits of freezing white bread (※) before eating it in 10 healthy adult men and women (aged 22 to 59) ( European Journal of Clinical Nutrition volume, 2007 ).
(* White bread is bread made from whole wheat flour with the bran and germ layers removed. This extends its shelf life, but it also has no dietary fiber, so sugar is more easily absorbed and blood sugar levels rise more easily.)
The experiment compared “homemade bread” with “commercially available bread,” and measured changes in blood sugar levels in subjects when they ate the bread as is, when it was frozen and then thawed, and when it was toasted after being frozen.
As a result, when frozen bread was thawed and then eaten, the rise in blood sugar level was reduced by 31% within two hours compared to when it was eaten as is .
What ‘s more, toasting the thawed bread enhanced the effect, reducing blood sugar rise by 39% .
This result is thought to be due to the action of resistant starch that increases when bread is frozen.
However, this effect was stronger in homemade bread and did not significantly change blood glucose levels in commercially available bread .
The researchers explain that the various chemicals contained in commercially available bread and differences in manufacturing methods may suppress the formation of resistant starch.
Therefore, you cannot expect any benefits from freezing sweet breads bought at convenience stores.
And it’s not just bread that offers these health benefits.
Resistant starch is also found in rice , potatoes, udon, pasta, etc., and it has been found that the amount of resistant starch increases when these foods are cooled.
In particular, frozen rice contains about 1.6 times more resistant starch than freshly cooked rice.
However, when you reheat cold rice in the microwave, the amount of resistant starch seems to decrease slightly, but it still contains more than freshly cooked rice.
However, when cold rice was heated with hot soup, there was no decrease in resistant starch. Therefore, it seems that eating curry or ochazuke with cold rice is effective.
On the other hand, it is dangerous to leave rice at room temperature for a long period of time to cool it down .
Be careful, as rice and wheat contain a bacterium called Bacillus cereus, which can multiply to dangerous levels and cause food poisoning if left at room temperature.
Either way, it seems certain that freezing bread and rice can be not only convenient but also beneficial in terms of health.