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

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.

The double burden of malnutrition is a key global development challenge. According to FAO in 2017 anaemia, principally caused by iron deficiency, was estimated to affect 1.62 billion people, while inadequate zinc intake was estimated to affect 17.3% of the global population. In contrast the consumption of high glycemic index (GI) and glycaemic load foods, alongside a decrease in physical activity and rapid urbanization, has contributed to the global escalation of non-communicable diseases (NCDs). In Eastern Asia type-II diabetes has increased at a greater rate than in western societies, with a high consumption of polished, white rice being a key contributor. White rice is a staple food of over one third of the worlds population, but the milling process removes many essential nutritional components, including micronutrients such as iron and zinc, vitamins, fatty-acids, phytochemicals and fibre, leaving a product with low nutritional value but a high GI, the starchy white rice being rapidly digested in the human intestine.

While coloured rice landraces are prized by many societies for their nutritional value and perceived medicinal qualities, thought to be due primarily to the high levels of the flavonoid polyphenols found in the seed coat (bran), the daily consumption of coloured rice varieties in the Philippines and Thailand is low. There has been much research on the effects of individual flavonoids on human nutrition and health, but far less on the natural variation of these polyphenols in rice, and even less on the influence of different polyphenols profiles on other nutritional factors such as micronutrient bioavailability, starch digestibility (GI) and dietary fibre content. Given the complex interplay between polyphenols, iron, starch and dietary fibre, it is essential to understand how these nutritional factors relate to each other, and in doing so identify genotypes where the ratios of each are nutritionally more beneficial.

Within this project we will examine how the polyphenols found in both coloured and non-coloured rice genotypes affect iron bioavailability, starch digestibility and dietary fibre content to identify rice genotypes with optimal polyphenol profiles to support maximum iron absorption and reduce the rate of starch digestion in the human intestinal tract. We will deliver a better understanding of the relationship between polyphenol profiles, iron bioavailability, starch digestibility and dietary fibre content in rice, research findings that will lead to high yielding rice varieties with improved nutritional value. We will also work with consumers, stakeholders and policy makers to better understanding of consumer awareness and acceptability of nutritionally valuable rice in rice-based diets and to increase capacity of policy makers, and co-development of nutrition intervention strategy to foster acceptance of nutritionally valuable rice.

Outputs from this project would initially have significant effects upon the health and economic welfare of the general populations in the Philippines and Thailand. However rice is consumed widely across Asia, Africa, South America and is growing in popularity across the developed world. Understanding the true value of polyphenols, and their relationship to other nutritional factors, will allow us to combine each of these dietary components to optimum advantage within the human staple of rice. The knowledge gained within SuperNutrientRice will have a much wider, global benefit to human health through its impact on reducing NCDs. Balanced nutrition throughout the human life course is crucial to ensure good physical and mental development, long-term health, productivity and income.