Improving the nutritional value and digestibility of rice to address double burden malnutrition in the Philippines and Thailand

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Rice (Oryza sativa L.) is a staple food for more than half of the world's population, with most rice being consumed as polished, white rice. However, the milling process removes many essential nutritional components, including essential micronutrients such as iron and zinc, vitamins, fatty-acids, phytochemicals and dietary fibre. This can lead to the development of micronutrient deficiencies among peoples for whom rice is the primary source of calories. Furthermore, white rice tends to have a high glycaemic index (GI), the starch being rapidly digested in the human intestine. The consumption of high GI and glycaemic load foods, alongside a decrease in physical activity and rapid urbanization, has contributed to the expansion of non-communicable diseases such as type-II diabetes, with the Philippines having the highest recorded levels. Thus, high consumption of white rice presents as a prime example of the double burden of malnutrition. Rice is very much part of the culture of many peoples, especially in Asia. Therefore a reduction in rice consumption is often not an acceptable option. Old local varieties, including coloured rice (black or purple, red to brown) have been shown to possess higher nutritional value and numerous health benefits, including anti-cancer, anti-diabetic and anti-hyperlipidaemic properties. Consequently there is growing interest among consumers for health-promoting food products, although this is primarily among higher-income consumers. In 2015 a successful purple rice variety was released in Thailand, RiceBerry. However, RiceBerry is low yielding and is currently directed at a high-income market. There is an urgent need to raise awareness of the value of coloured rice varieties among lower-income consumers, while breeding high-yielding rice varieties with improved nutritional value and low GI, without compromising consumer acceptance. This will benefit the millions of people who depend on rice, improving livelihoods and economies.Polished white rice is 90% starch, a complex carbohydrate made up of amylose and amylopectin that has a high GI. However, lowering the rate of starch breakdown in the gut (low GI) can lead to starch reaching the large intestine (colon) where it undergoes bacterial degradation (fermentation) in a manor analogous to dietary fibre, with consequential benefits to gut health. Work at IRRI has identified linkages between rice starch breakdown and the polyphenols found in red rice accessions. Kaempferol-derivatives, which act as alpha-amylase inhibitors, have been linked to low starch digestibility, while a red rice haplotype was found to be associated with altered amylose vs amylopectin ratios. While polyphenols are in general considered beneficial to human health, there have been reports that some polyphenols can inhibit iron bioavailability. Beneficial and antagonistic effects have also been associated with dietary fibre, e.g. promoting calcium, but limiting iron uptake. Phytates, which are the primary store of phosphorus in cereal grains, can also interfere with micronutrient bioavailability, binding other micronutrients, including iron and zinc. As monogastric animals lack sufficient amounts of appropriate phytate degrading enzymes, phytate is considered an anti-nutritional, having negative effects on the bioavailability of essential dietary minerals. Given this complex interplay between polyphenols, micronutrients and phytate, starch and dietary fibre on human health, this project aims to identify rice genotypes where the ratios of each optimise the nutritional and health benefits of rice, while maintaining consumer acceptability. Through the rice breeding programmes at our partner institutes in the Philippines and Thailand we aim to introduce these health benefit characteristics into high-yielding rice varieties. Through engagement with policy makers we aim to promote the uptake of coloured rice varieties by lower-income households in the Philippines and Thailand.