Does cooling rice really have a positive effect on blood sugar?
The nutrition and metabolism-focused website snaq.ai published a scientific report on the impact of refrigerating cooked rice on blood sugar levels, cautioning that the benefits widely circulated on social media may be exaggerated. The report clarified that while cooling cooked rice before consumption does indeed lead to the formation of a type of resistant starch, its effect on blood sugar levels remains limited and may not be clinically significant for many individuals.
In recent years, videos and posts have spread claiming that cooling rice before eating it completely prevents blood sugar spikes—an assertion that does not align with available scientific evidence.
Scientifically, this phenomenon is known as “starch retrogradation.” Cooling causes some starch molecules to reorganize into crystals that are difficult for digestive enzymes to break down, causing them to function more like fiber than rapidly absorbed carbohydrates. This process occurs when amylose starch molecules, which vary in proportion depending on the rice type, cool down and form new hydrogen bonds between them, making them more resistant to digestion. The amount of resistant starch formed varies by rice type; basmati and long-grain rice contain higher levels of amylose compared to short-grain rice, making them more responsive to the cooling process.
- A study on healthy individuals found that cooled and reheated rice contained 1.65 grams of resistant starch per 100 grams, compared to 0.64 grams in freshly cooked rice, showing a notable decrease in glucose response. However, this difference in resistant starch content equates to approximately 5 grams of carbohydrates per typical rice serving, an amount that may not be sufficient to produce a significant change in blood sugar levels for most people.
- A study involving 32 individuals with type 1 diabetes showed a reduction in peak glucose levels after consuming cooled rice, with the area under the curve dropping by more than half. However, the study also noted a significant increase in hypoglycemic episodes, suggesting that the effect may not be consistent or safe for all patients, particularly those relying on precise insulin dosages.
- A conflicting study found no statistically significant differences between cooled and fresh rice, indicating that the effect may not manifest in everyone and depends on individual factors such as digestion speed and gut microbiota composition, which vary from person to person.
Researchers emphasized that reheating does not negate the effects of cooling; on the contrary, studies showed that cooled and reheated rice contained higher amounts of resistant starch. This is because reheating does not break the hydrogen bonds formed during cooling, thereby preserving the structure of the resistant starch. However, the effect may vary depending on the reheating method, temperature, and duration.
Regarding different rice varieties, research has shown that basmati and long-grain rice produce more resistant starch than short-grain or sticky rice, due to their higher amylose content. Therefore, choosing the type of rice may have a greater impact than the preparation method, as basmati rice naturally has a lower glycemic index compared to short-grain white rice, even without cooling.
The report concluded that while the effect of cooling rice on blood sugar is real, it is modest, and portion size remains the most influential factor on the glycemic response. The amount of rice consumed has a greater impact on blood sugar spikes than the method of preparation, underscoring that controlling portion size remains the most effective strategy. They advised people with diabetes to consult their healthcare team before making changes to their usual meals, particularly regarding insulin dosages.
The report also cautioned against relying on cooling rice as a magic solution for blood sugar management, recommending instead that it be integrated into a comprehensive strategy that includes choosing low-glycemic-index rice varieties, controlling portion sizes, and adding proteins and vegetables to meals to slow digestion. They emphasized that small lifestyle changes, such as adding a spoonful of vinegar to rice during cooking, can have similar effects in lowering the glycemic index, without the need to cool the rice.
