Rice is generally thought to be a healthy addition to the diet because it is a source of fiber. However, not all rice is equally nutritious, and brown rice might have an unique advantage over white rice by offering protection from high blood pressure and atherosclerosis (“hardening of the arteries”), say researchers at the Cardiovascular Research Center and Department of Physiology at Temple University School of Medicine in Philadelphia.
New research by Satoru Eguchi, Associate Professor of Physiology, suggests that a component in a layer of tissue surrounding grains of brown rice may work against angiotensin II. Angiotensin II is an endocrine protein which causes blood vessels to constrict and known culprit in the development of high blood pressure and atherosclerosis.
Brown Rice and Angiotensin II
The subaleurone layer of Japanese rice, which is located between the white center of the grain and the brown fibrous outer layer, is rich in oligosaccharides and dietary fibers, making it particularly nutritious. However, when brown rice is polished to make white rice, the subaleurone layer is stripped away and the rice loses some of its nutrients. The subaleurone layer can be preserved in half-milled (Haigamai) rice or incompletely-milled (Kinmemai) brown rice. These types of rice are popular in Japan because many people there believe half-milled (Haigamai) rice and incompletely-milled (Kinmemai) are healthier than white rice.
The Temple team and their colleagues at the Wakayama Medical University Department of Pathology and the Nagaoka National College of Technology Department of Materials Engineering in Japan sought to delve into the mysteries of the subaleurone layer and perhaps make a case for leaving it intact when rice is processed. Because angiotensin II is a perpetrator in such lethal cardiovascular diseases, the team chose to focus on learning whether the subaleurone layer could somehow inhibit the wayward protein, angiotensin II, before it wreaks havoc.
First, the researchers removed the subaleurone tissue from Kinmemai rice (incompletely-milled rice). Then the researchers separated the subaleurone tissue's components by exposing the subaleurone tissue to extractions of various chemicals such as ethanol, ethyl acetate and methanol. They then observed how the subaleurone tissue affected cultures of vascular smooth muscle cells. Vascular smooth muscle cells are an integral part of blood vessel walls and are direct victims of high blood pressure and atherosclerosis.
During their analysis, the team found that subaleurone components that were selected by an ethyl acetate extraction inhibited angiotensin II activity in the cultured vascular smooth muscle cells. This suggests that the subaleurone layer of rice offers protection against high blood pressure and atherosclerosis. It could also help explain why fewer people die of cardiovascular disease in Japan, where most people eat at least one rice-based dish per day, than in the U.S., where rice is not a primary component of daily nutrition.
“Our research suggests that there is a potential ingredient in rice [subaleurone] that may be a good starting point for looking into preventive medicine for cardiovascular diseases,” said Dr. Eguchi. “We hope to present an additional health benefit of consuming half-milled or brown rice [as opposed to white rice] as part of a regular diet.”