RICE AND RISK OF TYPE 2 DIABETES
Around the world, the prevalence of type 2 diabetes continues to climb. The rate of increase is particularly high in countries such as China and India, the most populous nations on the planet. China and India are also similar in the sense that rice is their staple food. Although there have been changes in lifestyle, nutrition and physical activity, rice remains a favourite food. Indeed, rice provides about 20% of all calories eaten globally. White rice is still preferred over brown rice, but there have also been more subtle changes in milling and polishing that have altered the inherent nutritional properties of rice.
A long time ago, I recall reading a magazine article about the many different varieties of rice. Even though I had already devoted 4 years to training in Food Science, I was amazed to learn that ordinary people distinguished between different types of rice, favouring one versus another, depending on the cuisine. To me, at that time, rice was rice! I learned that some people liked Jasmine best – the grains were fluffy and slightly sticky. They clumped together, making them ideal for eating with chopsticks. Other varieties such as Basmati were not at all sticky and individual cooked grains could be picked out one at a time. Basmati was the favourite for curries and other Indian dishes.
Today, we can find many varieties of rice on supermarket shelves, including short grain, long grain, medium grain, Arborio (ideal for making risottos) and sushi rice (short-grain Japanese rice) for making sushi. There’s also black rice, red rice, wild rice and Doongara (Clever Rice™) – a new variety developed in Australia to compete with Basmati.
One of the first research projects that I was to carry out as a scientist was on the GI of different rices sold in Australia. We compared 10 different rice products – 3 were commercial rices with different levels of amylose starch, a waxy variety with only 2% amylose, a converted (parboiled) rice, a quick cooking brown rice, puffed rice cakes, rice pasta and rice bran. Amylose starch is a straight-chain molecule that lines itself in rows, making it more difficult to gelatinise than the other form of starch called amylopectin. Higher temperature and more water is needed to cook high amylose varieties of rice.
The GI values varied, ranging from medium to high on a scale where glucose = 100. The low amylose Pelde variety gave the highest GI (93), while the high amylose rice gave the lowest GI (64). The quick-cooking brown rice also had a very high GI (80), as did the brown rice pasta (92). Interestingly, white rice and brown rice have similar GIs. It was the variety that was important, rather than the grain size, degree of milling or parboiling.
So here once again, the GI concept turned conventional nutrition wisdom on its head. It was wrong to automatically assume that a brown rice would have a lower GI than white varieties.
In November 2020, the prestigious journal Diabetes Care, carried a paper and editorial about the link between eating rice in large amounts and the risk of developing type 2 diabetes. The PURE study was an observational study in over 130,000 individuals from 21 countries. On average, people were followed-up for 10 years, during which time just over 6000 developed diabetes.
The authors found that those who ate more than 450 g per day (that’s around 2.5 cups of cooked rice) were more likely to have a diagnosis than those who consumed less than 150 g per day (less than 1 cup). In scientific wording, their risk was 20% more.
However, people from South Asia (India) were substantially (60%) more likely to have developed diabetes when rice was eaten in large amounts. People from South East Asia, the Middle East, South America and Africa were also more at risk, but not as much as those from South Asia. Surprisingly, there was no association between the amount of rice consumed in China and the risk of diabetes.
These mixed findings are difficult to explain on the grounds of differences in GI alone. We know that a diet with a higher GI and glycemic load will increase the risk of type 2 diabetes, but in the PURE study, the lower GI variety (Basmati) is associated with more diabetes than the higher GI variety consumed in China.
There are other possible explanations, e.g., the presence of toxic elements such as arsenic in rice grown in India. Also, some have interpreted the results of the PURE study as an indicator of a “poverty diet”, rather than nutrition. Most study participants located in low-income countries subsisted almost entirely on carbohydrates, “especially from refined sources.” A “poverty diet”, which is common in poor rural areas, is also typically high in sodium and low in animal products and vegetable oils. In this situation, it is extremely challenging if not impossible to separate the effects of diet from poverty and undernutrition.
Indeed, the South Asian (Indian) diet is higher in saturated fat (ghee is a popular cooking fat) that increases insulin resistance and the demand for insulin secretion. Over time, insulin resistance worsens, and the beta-cells eventually fail, despite the rices lower GI. Moreover, in China, the alternative to high GI rice is a large range of wheat products (including bread and dumplings) that also have a high GI.
And finally, as I often say to my students and colleagues, nutrition science is still very young, it’s very complex and we have lots to learn.
- White Rice Intake and Incident Diabetes: A Study of 132,373 Participants in 21 Countries
- PURE study makes headlines, but the conclusions are misleading
- Dietary Glycemic Index and Load and the Risk of Type 2 Diabetes: A Systematic Review and Updated Meta-Analyses of Prospective Cohort Studies
Professor Jennie Brand-Miller holds a Personal Chair in Human Nutrition in the Charles Perkins Centre and the School of Life and Environmental Sciences, at the University of Sydney. She is recognised around the world for her work on carbohydrates and the glycemic index (or GI) of foods, with over 300 scientific publications. Her books about the glycemic index have been bestsellers and made the GI a household word.