White bread, along with rice and pasta, is a major source of refined carbohydrates, which undergo processing that strips them of fiber and essential nutrients. Consuming these types of carbohydrates leads to a rapid spike in blood sugar levels, overburdening the pancreas and prompting it to release large amounts of insulin, which can increase the risk of developing diabetes over time.
Also, the lack of fiber in white bread makes it digested quickly, which reduces the feeling of satiety and leads to increased appetite and the desire to eat during short periods of time.
However, freezing bread alters the structure of its starch, its primary carbohydrate, through a process known as "reduction," where the starch molecules become more rigid and harder to digest. This results in the formation of what is called "resistant starch," which is not easily converted into glucose and therefore does not cause a sharp rise in blood sugar levels. It also promotes a feeling of fullness similar to fiber.
This benefit is not limited to bread alone, as recent studies indicate that rice, pasta and potatoes also acquire resistant starch when cooked and then cooled.
Canadian registered dietitian and medical writer Avery Zinker explains that resistant starch slows the absorption of other carbohydrates into the bloodstream, reducing the severity of glucose and insulin spikes, helping to stabilize energy levels throughout the day, and limiting sudden hunger pangs.
Zinker explained that starch is made up of two types of glucose polymers, amylose and amylopectin, and that the heat produced by the baking process breaks down the bonds between these molecules and makes them easily digestible, while cooling or freezing rearranges them into crystalline structures that are difficult for the body to digest, which explains the formation of resistant starch.
Fresh white bread contains a low percentage of resistant starch, ranging between 0.5 and 1.7% of its weight, but this percentage may rise to between 1 and 3% after freezing or cooling and then thawing.
Increased consumption of resistant starch is linked to several health benefits, including aiding weight loss and improving insulin sensitivity. A previous study showed that people who consumed resistant starch for approximately eight weeks lost more weight than the control group.
Other studies have also found that toasting bread after freezing and thawing reduces the body's response to glucose compared to unfrozen bread, which is likely due to an increase in the formation of resistant starch.
Experts recommend freezing bread for at least 12 to 24 hours to take advantage of this process, with the possibility of keeping it in the freezer for a period ranging between three and six months.
Zinker notes that resistant starch may also affect appetite regulation by stimulating the production of the hormone "GLP-1" in the intestines, a natural hormone that contributes to reducing hunger and slowing digestion, and which is mimicked by some modern weight-loss drugs.
Despite these benefits, experts emphasize that the effect of resistant starch remains limited, stressing the importance of moderation in consuming refined carbohydrates, with a preference for whole grains whenever possible, within a balanced diet.
