A method of preparing rice has been developed by scientists in Sri Lanka that could reduce the number of calories absorbed by the body by up to 60%.
The team from the College of Chemical Sciences experimented with 38 different types of rice from Sri Lanka, to develop a new way of cooking rice that increased the resistant starch content, a factor that could help prevent against health conditions like obesity and type 2 diabetes.
In preparing the rice, the team added a teaspoon of coconut oil to boiling water. They then added half a cup of rice and simmered this for 40 minutes, although the researchers said one could boil it for 20-25 minutes instead. Then, they refrigerated it for 12 hours. This procedure increased the resistant starch by 10 times for traditional rice.
Eating cold rice can reduce the number of calories being absorbed by the body. Image credit: Anoja Megalathan, Institute of Chemistry, College of Chemical Sciences, Sri Lanka
When starch is cooked in water and then cooled it changes shape and this new structure is resistant to enzymes (proteins) in our body and so cannot be digested. This is known as ‘resistant starch’ that passes through the body without being digested until it reaches the colon where it acts like fibre and feeds ‘good bacteria’ in the body.
The findings were recently presented at the 249th National Meeting and Exposition of the American Chemical Society (ACS).
Sudhair A. James, team leader at the College of Chemical Sciences, Sri Lanka, said: “Because obesity is a growing health problem, especially in many developing countries, we wanted to find food-based solutions. We discovered that increasing rice resistant starch concentrations was a novel way to approach the problem.”
A cup measurement of rice is loaded with starch (1.6 ounces in a cup), which is equal to around 240 calories per cup.
James added that "if the best rice variety is processed, it might reduce the calories by about 50-60%," when specific heating and cooking methods were followed.
He explained that starch can be digestible or indigestible. Unlike digestible types of starch, resistant starch is not broken down in the small intestine, where carbohydrates normally are digested into glucose and other simple sugars and absorbed into the bloodstream. Therefore, the researchers reasoned that if they could transform digestible starch into resistant starch, then that could lower the number of usable calories of the rice.
James said: “After your body converts carbohydrates into glucose (sugar), any leftover fuel gets converted into a polysaccharide carbohydrate called glycogen. Your liver and muscles store glycogen for energy and quickly turn it back into glucose as needed. The issue is that the excess glucose that doesn't get converted to glycogen ends up turning into fat, which can lead to excessive weight or obesity.”
The lower calories in the food are caused by oil entering the starch granules during cooking, changing its properties so that it becomes resistant to the action of digestive enzymes. This means that fewer calories ultimately get absorbed into the body.
James said: “The cooling is essential. Cooling for 12 hours will lead to formation of hydrogen bonds between the amylose molecules outside the rice grains which also turns it into a resistant starch.”
He added that reheating the rice for consumption does not affect the levels of resistant starch.
The research team are now planning to complete studies with human subjects to learn which varieties of rice might be best suited to the calorie-reduction process. The team also will check out whether other oils besides coconut have this effect.
Previous research has highlighted the risks of reheating cooked rice as some food poisoning bugs can survive cooking. It is recommended that rice should be served either hot or cooled and then stored in a fridge, as bacteria can multiply when the rice is left standing at room temperature.
Pam Dyson, Specialist Diabetes Dietitian at Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM) and author of the DRWF leaflet, A healthy diet and diabetes, said: “There has been a lot of interest in the role of resistant starch and its effect on weight and blood glucose levels over the past few years, and this article describes a method of increasing the resistant starch content of rice, with claims that this can reduce the energy (calories) by 50-60%.
“As rice is the number one staple food globally, feeds half the world’s population and provides up to 80% of energy intake for 3.3 billion people in Asia, this has the potential for a significant effect on the health of large populations at risk of obesity or type 2 diabetes. However, it is important to remember that the energy reduction shown in this study has not yet been tested in long-term, randomised controlled trials in humans and so the full effect of eating rice cooked by this method on body weight control has yet to be proven. Similar claims have been made for other cooked, cooled and re-heated starches such as pasta, potato and corn porridge, but at present the only evidence available is from short-term feeding studies that have measured blood glucose levels immediately after meals. This lack of long-term data does limit conclusions.
“There are some other issues that should be considered. To reduce the risk of food poisoning, food should be cooled rapidly after eating and stored in a refrigerator and then re-heated thoroughly - or eaten cold, which will affect taste and enjoyment. It also requires some forward-planning, so that food for tomorrow is cooked and cooled today. Overall, more information is needed before recommending cooled starches for weight control.”
A previous report on the benefits of eating reheating pasta can be read here
The DRWF leaflet A healthy diet and diabetes can be read here