Nutritional content of rice compared to other staple foods
White, long-grain rice: Raw, long-grain white rice is a relatively good source of energy, carbohydrates, calcium, iron, thiamin, pantothenic acid, folate and vitamin E, compared to maize, wheat and potatoes. It contains no vitamin C, vitamin A, beta-carotene, or lutein+zeazanthin, and is notably low in fiber.
Colored rice: Brown rice retains the bran layer (containing many vitamins and minerals as well as fiber), as this has not been polished off to produce white rice. Red rices are known to be rich in iron and zinc, while black and purple rices are especially high in protein, fat and crude fiber. Red, black and purple rice get their color from anthoncyanin pigments, which are known to have free-radical-scavenging and antioxidant capacities, as well as other health benefits.
The calorie content of 1 cup of cooked rice varies from a high of 241.8 kcals for medium-or short-grain white rice, to 218.4 kcals for medium-grain brown rice, 216.5 kcals for long-grain brown rice, 205.4 kcals for regular long-grain white rice, to a low of 165.6 kcals for ‘wild rice’.
Preparation for consumption: effects on nutrition
Washing or rinsing rice before cooking: This is common practice in places where rice packaging and storage methods leave rice exposed to dust and other contaminants. Rinsing rice, sometimes multiple times, results in the loss of water-soluble nutrients, including starch, protein, vitamins, minerals and fats. Use of clean packaged rice reduces or removes the need for washing and thus prevents the loss of nutrients (fao.org). Similar nutrient loss would also occur, however, if rice is pre-soaked and then drained before cooking, or if rice is cooked in excess water that is drained away before consumption.
Cooking: Cooking milled (polished/white) rice by boiling in water (without washing) results in the loss of up to 7% of protein, 36–58% of crude fat, 16–25%
of crude ash, 21% of calcium, 47–52% of thiamine, 35–43% of riboflavin, and 45–55% of niacin.
Wet milling: Water-soluble nutrients are also lost during wet milling of rice flour (a process used for making rice noodles, egg roll wrappers, and some rice-flourcakes, etc.), in the filtration step. This includes vitamins, minerals, free sugars and amino acids, water-soluble polysaccharides, protein (albumin), fat and starch.
Parboiling: Parboiling rough rice before milling, as is common in India and Bangladesh, allows a portion of the vitamins and minerals in the bran to permeate the endosperm and be retained in the polished rice. This treatment also lowers protein loss during milling and increases whole-grain recovery.
Fermentation: Fermentation of rice is another popular preparation method.Reportedly, protein content of fermented rice decreases from 1.54% after one day of fermentation to 1.14% after three days at 70% moisture.
Glycemic Index (GI)
GI is a measure of the relative ability of carbohydrates in foods to raise blood sugar levels after eating. High GI food is easily digested and absorbed by the body, which can result in fluctuations in blood sugar levels. Foods with low GI, on the other hand, are those with slow rates of digestion and absorption, causing a gradual and sustainedrelease of sugar into the blood, which is beneficial to health and reduces the chances of developing Type II diabetes.
Slow digesting starches lower the body’s insulin response, thus helping people with diabetes to normalize their blood sugar. Currently, 285 million people, mostly in developing countries, have Type II diabetes and another 344 million are at risk of developing it due to impaired glucose tolerance. If diabetes is undiagnosed, it leads tochronic conditions and death. Consumption of cereals is not necessarily a cause of Type ll diabetes, but cereals containing particular structures of starch offer a solution for prevention and management of the condition.
GIs of 55 or less are considered ‘low’, those of 56–69 are ‘medium’ and those of 70 and above are ‘high’. A study of 235 types of rice from around the world, by IRRI and CSIRO's Food Futures Flagship, found that the GI varies by type of rice, from a low of 48 to a high of 92 (average 64), with most scoring a low to medium GI. This means that rice and rice products can be part of a healthy diet for the average consumer and part of a low GI diet to help those with Type II diabetes better manage their condition.The research team also identified the key gene that determines the GI of rice. This will enable rice breeders to develop varieties with different GI levels to meet consumer demand for rice and rice-based food products.
Effect of environmental and crop management factors on nutritional content
High-nutrient rice of the future
Human micronutrient deficiencies are relatively severe in areas where rice is the major staple. Often, calorie demand is met by an increase in rice without a corresponding increase in other foods such as legumes or fish. Increasing the density of provitamin A carotenoid, iron, and zinc in rice can alleviate these deficiencies, especially among the urban and rural poor people who have little access to alternatives such as enriched foods and diversified diets. Research is under way to fortify rice with micronutrients in areas where these are inadequate in the diet. It is still debated whether such micronutrient increases in the endosperm are sufficient to significantly affect human nutrition. These fortified rice varieties are being tested in nutrition trials before farmers grow them commercially. To drive the adoption of micronutrient-rich varieties, the improved traits will need to be combined with other traits that are attractive to farmers, such as tolerance of drought, salinity, or submergence.
Vitamin A: A severe lack of Vitamin A causes irreversible blindness. Golden Rice is a new type of rice that contains beta carotene, a source of vitamin A. IRRI is working with leading nutrition and agricultural research organizations to develop and evaluate Golden Rice as a potential new way to reduce vitamin A deficiency in the Philippines and Bangladesh. Work to develop Golden Rice currently includes laboratory, greenhouse, and field studies at IRRI, national agricultural research institutions, and other institutions to: develop Golden Rice varieties that are well suited for rice-growing environments and consumer preferences in Asia; help assess the safety of Golden Rice; evaluate whether consumption of Golden Rice improves vitamin A status; and explore how Golden Rice could reach those most in need.
Iron: Anemia affects more than 2 billion people globally, with women and children most at risk. Deficiency in dietary iron is a main cause of anemia. It is the most common and widespread nutrition problem, together with deficiency in zinc, iodine, and vitamin A. Iron deficiency and iron deficiency anemia cause a range of health problems in humans, including increased chances of maternal and child mortality and negative impacts on cognitive and physical development of children. They also affect an individual’s physical performance, especially the work productivity of adults. Unfortunately, polished white rice contains low amounts of iron – popular varieties studied in the Philippines and Vietnam were found to generally contain 2–3 milligrams of iron per kilogram (ppm) of rice, reaching a maximum of 5 ppm in some cases. Breeders at IRRI are working to create ‘iron-clad’ rice with a minimum of 14 ppm of iron. The main advantages of developing varieties with high iron content are that this is a food-based approach and delivering the solution in such a widely consumed crop could contribute to a large effect.
Zinc: Billions of people in the developing world are at risk of zinc deficiency. In Southeast Asia alone, 71% of the population suffers from zinc deficiency. Ample genetic diversity in rice for grain zinc content exists and we have developed three lines of high-zinc rice with the Bangladesh Rice Research Institute (BRRI), which are now in advanced yield trials in Bangladesh. In collaboration with Bangladeshi institutions, the University of California at Davis, HarvestPlus, and other international organizations, we are also investigating the bioavailability of zinc in rice. IRRI is also looking into management practices that increase zinc uptake of the rice plants so that there is more zinc in the grain.
Folic acid: Women with folate deficiency are more likely to give birth to low-birth-weight and premature infants and infants with neural tube defects. A deficiency of folate occurs when dietary intake of folate is inadequate. This is a worldwide problem and some foods are required to be fortified, such as wheat flour. Rice contains little or no folate (B9). Major breakthroughs have been made in recent years in transgenic rice expressing significant levels of folate. Research is ongoing.
Protein: Breeding efforts to increase protein have been largely unsuccessful because of the considerable effects of environment and because of complex inheritance properties in the triploid endosperm tissue.