The association between the risk of diabetes and white rice consumption in China: Existing knowledge and new research directions from the crop perspective

HUANG Min

Rice and Product Ecophysiology,Key Laboratory of Ministry of Education for Crop Physiology and Molecular Biology,Hunan Agricultural University,Changsha 410128,P.R.China

China has the most people with diabetes in the world (IDF 2021),and the promotion of a healthy diet is a key public health priority for controlling the prevalence of diabetes in China (Hu 2011). Rice (mainly white rice) is a staple food for more than 60% of the Chinese population (Hu and Sheng 2021). Because white rice has the husk,bran,and embryo completely removed during the milling process,it is low in the dietary fiber,micronutrients,and polyphenols that are conducive to glucose metabolism (Aryaeianetal.2017;McRaeetal.2018;Barraetal.2021). In addition,white rice is high in carbohydrates (starch) and generally has a high glycemic index (GI) (Atkinsonetal.2021),meaning that consumption in large amounts may cause high postprandial levels of blood glucose and insulin,and consequently reduce insulin sensitivity and pancreatic β-cell function (Liveseyetal.2019). These factors suggest that a higher consumption of white rice may increase the risk of diabetes.

Another rice trait that may lead to a high risk of diabetes associated with high white rice consumption is related to arsenic exposure. Compared to other cereal crops such as wheat and barley,rice is more efficient in the uptake and translocation of arsenic (Suetal.2010),which is widely distributed in soil,water,and air and is highly toxic in its inorganic form (Chungetal.2014).White rice has an inorganic arsenic (iAs) content more than 10 times higher than other cereals (TatahMentanetal.2020). iAs exposure has been shown to increase insulin resistance and reduce pancreatic β-cell function by increasing cytokine levels,inhibiting proliferativeactivated receptors,inducing oxidative stress,activating nuclear factor Kappa B,and increasing amyloid formation in the pancreas (Bell 2015). A positive dose-response relationship between the risk of diabetes and the amount of iAs exposure has been also found;namely,the risk of diabetes increases by 13% for each 100 µg L–1increase of iAs in drinking water (Wangetal.2014). Based on the average daily rice (mainly white rice) consumption rate per capita (210 g;OECD-FAO 2022),the recommended daily water intake rate (1.5–1.7 L;CNS 2022),and the average iAs content in white rice (103 µg kg–1;Lietal.2011) in China,the estimated daily consumption of iAs in white rice is equivalent to 12.7–14.4 µg L–1of iAs in drinking water,so the risk of diabetes increases by 1.7–1.9% due to iAs exposure from white rice consumption in China.

Several studies have investigated the association of diabetes risk with white rice consumption in China,but the results are inconsistent. For example,Villegasetal.(2007) carried out a prospective cohort study and found a relative diabetes risk of 1.78 among women who consumed 750 g d–1of cooked rice (～250 g d–1of uncooked rice) compared with 500 g d–1. Similarly,Huetal.(2012) carried out a meta-analysis which showed that a higher risk of diabetes was associated with higher consumption of white rice in Asian populations,including Chinese people. However,more recently,Bhavadharinietal.(2020) conducted a Prospective Urban Rural Epidemiology study that found no significant association between the risk of diabetes and white rice consumption in China.

Nevertheless,the risk of diabetes associated with white rice consumption in China may be increasing due to changes in the socioeconomic and physical environments that are associated with rice production. First,as living standards improve,the demand for and consumption of high eating-quality rice,mainly soft-textured rice with low amylose content,has increased considerably in China (Huang and Hu 2021). To cater to the changing consumer needs,more new rice varieties with low amylose content have been developed and grown in China. For example,in the middle reaches of the Yangtze River,the average amylose content declined significantly from 20% in the rice varieties released during 2006–2009 to 16% in those released during 2019–2021 (Huangetal.2022d). However,the development of low amylose rice in China has resulted in a substantial acceleration in the rate of digesting starch into glucose in cooked rice and consequently a higher GI (Huangetal.2022a,b,c,e). Foods with a higher GI can cause increases in postprandial blood glucose and insulin levels,reductions in insulin sensitivity and pancreatic β-cell function,and hence increase the risk of diabetes (Liveseyetal.2019).

Second,climate warming is being documented around the world. An increase in temperature during the grainfilling period can result in a reduced grain amylose content in rice varieties with originally low amylose content (Zhongetal.2005;Yamakawaetal.2007;Yinetal.2020;Huangetal.2022a),because it can reduce both the activity of granule-bound starch synthase and the transfer of glucosyl residues from ADP-glucose to its glucan substrate,which consequently generates fewer amylose molecules (Zeemanetal.2010;Ahmedetal.2015). Moreover,climate warming can increase arsenic availability in soils and the iAs content in rice grains(Neumannetal.2017;Mueheetal.2019). Either the reduced amylose content or the increased iAs content in rice grains may lead to a higher risk of diabetes associated with rice consumption.

While white rice is low in dietary fiber,micronutrients,and polyphenols but high in carbohydrate (starch) and iAs,there is no consistent evidence that a higher risk of diabetes is associated with higher consumption of white rice in China. However,the development of rice varieties with low amylose content and climate warming may increase the risk of diabetes associated with white rice consumption in China by increasing the GI of cooked rice or/and increasing the iAs content in rice grains.This highlights the need to fully evaluate the individual and combined effects of the increases in GI and the iAs content on the risk of diabetes associated with white rice consumption. This evaluation should consider the potential change in per capita consumption of rice. With a shift to other types of food,such as meat and vegetables,the rice consumption rate per capita is experiencing a downward trend in China (Secketal.2012). In addition,it is also important to develop comprehensive crop,soil,and climate strategies to prevent an increase in the GI of cooked rice and an increase in the iAs content in rice grains,with the goal of avoiding the potentially increased risk of diabetes associated with white rice consumption.