With the growing prevalence of diet-related health conditions, such as obesity, diabetes and cardiovascular disease, there is a real need to increase the availability of healthier staple foods. Consumers are also seeking out a wider range of food options that meet their expectations for health and wellbeing and help them better manage their weight.
According to Tony Bird, CSIRO Food Futures Flagship researcher, low GI diets offer an opportunity to address some of these needs. “Studies show that the risk of chronic diseases like type 2 diabetes is strongly related to the GI of the overall diet,” he said.
Foods with a high GI are readily digested and absorbed by the body, which often results in marked fluctuations in blood sugar levels that can increase the chances of getting type 2 diabetes in the future and make management of the condition difficult.
Conversely, carbohydrate foods with a low GI allow a gradual, more even and sustained release of sugar into the blood, which has been linked to a range of health benefits, including reducing the chances of developing diabetes.
“Low GI diets may help control appetite and delay hunger and therefore may assist with weight management. They are also associated with other positive health outcomes, for instance helping to reduce risk factors for coronary heart disease” said Bird.
The GI of rice
Rice has often been caught up in the debate about diet, weight, carbohydrates and GI, but a recent study has found that rice can be part of a low GI diet. The study analysed 235 types of rice from around the world and found its GI varies considerably, with most varieties scoring a low to medium GI.
The research was conducted by CSIRO’s Food Futures Flagship and the International Rice Research Institute (IRRI), a non-profit independent research and training organisation based in the Philippines. The study found that the GI of rice ranges from a low of 48 to a high of 90, with an average of 64 (low GI foods are those measured 55 and less, medium GI are between 56 and 69, while high GI measures 70 and above).
Measurement of the 235 varieties of rice in the study was conducted using a prototype of a fully automated ‘artificial gut’ developed by the Food Futures Flagship. The first of its kind, it predicts the GI in a range of foods and has undergone extensive testing by CSIRO to verify its accuracy. The reference foods were selected on the basis that they are representative of everyday starchy foods eaten in Australia, they span a broad range of GI values and food groups and are commercially processed and shelf-stable products.
Melissa Fitzgerald, who led the IRRI team, said the wide range of GI levels found in rice was the most surprising finding. “Most of the work up until our study had indicated that rice was a high GI food, yet the lowest GI was 48 which is actually really low and a lot were in that 50 to 65 range and that’s only a medium,” she said.
“In fact, half way through our study there were a number of other studies published that really demonised white rice. We suspected that rice wasn’t the villain it was being made out to be, so we were keen to have the evidence to back this up. There was also the feeling among many, particularly in Asia, that if you develop diabetes you should stop eating rice. So we felt there was a real need to be able to show diversity in the GI of rice which would provide the opportunity for those at risk to choose a variety that is low in GI.”
Different rice, different GI
The study found that varieties such as India’s most widely grown rice, Swarna, and other rice such as Doongara and Basmati which are available in Australia, have a low to medium GI. The rice variety measured to have the lowest GI is actually one from a breeding line from IRRI, the second lowest was an old Chinese variety, Shan-Huang Zhan 2. Varieties from Bangladesh, Sri Lanka and India had low GI as well as many of the popular varieties from happy wheels South Asia while those in Southeast Asia were at the slightly higher end of GI values, with an average of about 70.
Understanding that different types of rice have different GIs will allow consumers to make informed choices about the types of rice they want to eat, and provide important information for nutritionists to identify and quantify the impact of low GI rices on blood sugar.
The findings of the study are good news for people with or at risk of certain chronic diseases, as it means they can select the right rice to help maintain a healthy diet, according to Tony Bird. Substituting a high GI rice with a lower GI rice is a simple way to lower the GI of a meal.
Researchers also found that a well-known rice gene, the waxy gene, plays a major role in determining the GI of rice.
Fitzgerald explains that the gene occurs in five different forms in rice, which accounts for the range of GI levels seen. “It’s a bit like the gene for eye colour,” she said. “You’ve got one eye colour gene and you can get that in blue or green or brown, while for the GI gene in rice you can get it in low, very low, intermediate, high or very high. So its those different forms of that gene that associate with GI. What’s really significant about this discovery is that it offers rice breeders the opportunity to develop varieties with different GI levels.”
Future development of low GI rice would also enable food manufacturers to develop new low GI food products based on rice. Although making better food choices is the ideal strategy for reducing chronic disease, according to Tony Bird meaningful behavioural change is difficult to achieve in practice. ‘That’s why lowering the GI of staple foods such as rice is likely to be more effective in promoting public health, especially in communities in which rice makes up a significant part of the diet,” he said.
Food manufacturers have the opportunity to use the artificial guy technology used in the study through Next Instruments. According to Bird the device, which works by mimicking the human digestion process, was originally developed to test the properties of new grains being developed by CSIRO. “It’s much quicker and more cost-effective than the current method,” he said.
“Until now predicting GI involved feeding the test food to a number of human volunteers and taking regular blood samples over the following hours to monitor changing blood sugar levels. This new machine can replace this expensive and time consuming process of testing in humans, thereby expediting the early phases of product development and improvement, leaving the standard in vivo (human) test to the final stage of food development and labelling procedures.”
The NutriScan G120 Glycemic Index Analyser provides food manufacturing companies and laboratories worldwide with an accurate means of testing the functional properties and potential human health benefits of new foods. Launched at the Pittcon conference and exposition on laboratory science in Atlanta, US, in March last year, it has since been showcased around the world.
“The most interesting comment from potential customers has been that the analyser is not just useful to measure GI but can also be used for other applications, such as lipid profiles, protein profiles and drug breakdown studies,” said Phillip Clancy, managing director of Next Instruments.
“Customers have realised that they could use the G120 with a different set of enzymes and alternate detection systems to measure a range of nutrients present in the digestion process.”
Bird said the principal purpose of the device is to help food manufacturers develop a wider range of healthy food products far more cheaply and quickly than previously possible. “It can also be used to screen food ingredients on the basis of their glycemic properties or germplasm for functional grain attributes,” he said.
“With the growing problem of obesity, diabetes and cardiovascular disease in Australia and around the world, there is increasing demand for low GI foods. People need greater access to products with appropriate health benefits, and we believe this GI testing device will help achieve that gold.
Source: Food Australia