Consumption of Brown Rice Reduces Desire for Fat

In the US, as well as many other countries, grains such as rice, make up a significant part of the average persons diet. However, during the process of refining grains like rice, as well as wheat and barley etc., the outer parts (bran) are removed. The bran contains multiple nutrients and bioactive compounds that are thus lost to our diets. Many recent studies have demonstrated diets rich in whole grains improve insulin responsiveness and reduce the incidence of type 2 diabetes. Brown rice is indeed one of the grains known to exert this positive effect on the prevention of diabetes. Until recently, although it was known that consumption of brown rice exerted these effects, it was not clear as to what was the mechanism of these effects of brwon rice.

The bran of brown rice, like all grain brans, is rich in antioxidants, phytosterols, and other beneficial nutrients. One of the more bioactive components of brown rice is known as gamma-oryzanol which is a mixture of ferulic acid esters and phytosterols. Ferulic acid is a hydroxycinnamic acid which is an  abundant phenolic phytochemical found in many plants.

A recent study published online in the journal Diabetes, (http://diabetes.diabetesjournals.org/content/early/2012/07/11/db11-1767.abstract?sid=78185278-fee8-452d-81e4-8c3dd1822305) now shows that the mechanism of action  of brown rice, and in particular gamma-oryzanol, is via the prevention of cellular stress within the region of the brain called the hypothalamus. The hypothalamus is the major appetite and energy expenditure regulatory structure in the brain. For more information on how the hypothalamus regulates appetite and feeding behaviors visit the Gut-Brain Interactions page at themedicalbiochemistrypage.org.

When laboratory mice given free access to a diet that consisted of brown rice-containing chow as well as a chow that was high in fat the mice significantly preferred to eat only the brown rich chow and ignored the high fat chow. This result indicates a strong correlation between consumption of whole grains such as brown rice and a decrease in the desire to consume fatty foods. This same result was obtained with mice if they were orally administered gamma-oryzanol. In addition to the effects on food preference by consumption of brown rice, the mice exhibited improved glucose tolerance and showed a reduction in endoplasmic reticulum (ER) stress within the hypothalamus. When the mice were administered 4-phenylbutyric acid, which is a chemical chaperone that prevents ER stress they preferred the brown rice chow over the high fat chow and exhibited increased glucose tolerance. These results suggest that gamma-oryzanol likely functions as a chemical chaperone and prevents ER stress in the hypothalamus thus resulting in the altered feeding behaviors. Of note is that ferulic acid itself is known to produce a reduction on ER-stress when added to nerve cells in culture. It is also important to point out that the consumption of brown rice did not result in alterd levels of circulating insulin indicating that the altered dietary preferences were insulin-independent.

When the expression of ER stress genes was analyzed in these studies, brown rice-fed mice demonstrated a significnat reduction overall expression within the hypothalamus. Increases in hypothalamic ER stress are known to provoke resistance to leptin resulting in increased feeding and ultimately obesity. In addition, hypothalamic ER stress is known to cause an increased preference for a fatty diet.

The major take-home from this study is that the principal mechanism by which the known effects of whole grains and brans on glucose tolerance and diabetes, is exerted via the attenuation of ER stress within the major appetite and feeding control center of the brain, the hypothalamus.

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