Riceabetes: is the association of type 2 diabetes with rice intake due to a high carbohydrate intake or due to exposure to excess inorganic arsenic?

Abstract

A high intake of rice is associated with a high incidence and prevalence of diabetes. While this may be partially due to the high glycemic index carbohydrate content, it may also be due to a high arsenic level found in rice. Arsenic increases insulin resistance and decreases beta-cell function through oxidative stress, high cytokine levels, activation of NF-kappa B and increased amyloid formation in the pancreatic beta cells.

Keywords:

• Rice intake
• high arsenic levels
• insulinresistance
• beta-cell dysfunction
• type 2 diabetes

It is generally assumed that a high carbohydrate diet is, in addition to obesity, a high fat intake and a sedentary lifestyle, a major factor in the pandemic of diabetes. Since rice is a high glycemic index carbohydrate, it is not surprising that a rice-based diet has been associated with a higher incidence and prevalence of type 2 diabetes. However, rice’s glycemic index may not be the major or only cause of the association of a high rice intake with diabetes. An alternative explanation is that rice has a high inorganic arsenic content which with a high rice intake is diabetogenic.

Worldwide, a higher consumption of white rice has been shown in a meta-analysis to be associated with a significantly increased risk of type 2 diabetes especially in Asian populations.[1] The risk was increased by 55% (CI 1.20–2.01) when the highest to lowest category of white rice intake in Asian populations were compared, whereas in Western populations the risk was increased by 12% (CI 0.94–1.33 p = 0.038). Overall, for each daily serving of rice, the relative risk of type 2 diabetes increased by 11% (CI 1.08–1.14).[1] In the United States, white rice consumption is still relatively low but the intake has tripled since the 1930s to the current intake of 20.5 lbs per year. An increased intake of white rice has been shown to be associated with an increased prevalence of diabetes in three prospective US adult studies (two Nurses Health Studies and the Health Professional Follow-up Study). In these studies, a white rice intake of more than five servings per month compared with less than one serving per month was associated with a 17% statistically significant increase in the incidence of diabetes (CI 1.02–1.36).[2]

Due to its palatability, white rice is the most commonly eaten form of rice throughout the world. Through the refining process, the outer bran and germ portions of brown rice are removed, leaving a starchy end product (white rice) which has a lower fiber content as well as a lower content of vitamins and minerals.[3] Therefore, white rice has a greater carbohydrate content and a high glycemic index (64%), which may account for the increased risk of type 2 diabetes with white rice.[4,5] Salmeron et al. have shown in large epidemiological studies that diets with a high glycemic load and a low cereal fiber content are associated with an increased risk of developing diabetes in both men and women.[6,7] However, white rice’s high glycemic index may not be the only explanation for the increased incidence of type 2 diabetes with a high intake of rice.

Recently, the Federal Drug Administration (FDA) has released warnings that rice contains excessive quantities of arsenic and recommended that children only consume rice pasta or rice cereal once every two weeks.[8] Exposure to inorganic arsenic has also been shown to be associated with an increased risk of developing type 2 diabetes. In the 2003–2004 National Health and Nutrition Examination Study (NHANES), subjects with type 2 diabetes had a 26% higher urinary arsenic level (CI 2.0% to 56.0%) than nondiabetic subjects.[9] In villages in Taiwan that are exposed to a high environmental arsenic level, the prevalence of diabetes in those between the ages of 65 and 74 years who had a long-term exposure was 5.5-fold higher (CI 2.2–13.5) than in those villages that had a low arsenic exposure.[10]

A likely mechanism by which a high exposure to arsenic results in the development of diabetes is through interference with the PKB/Akt-dependent mobilization of GLUT4 transporters which results in insulin resistance.[11] However, exposure to high levels of arsenic can also increase beta cell dysfunction. High arsenic levels lead to increased levels of two cytokines (tumor necrosis factor alfa and interleukin-6) which are associated with insulin resistance. Insulin resistance is also increased by inhibition of proliferative-activated receptor gamma (PPAR gamma), a nuclear hormone receptor which increases insulin sensitivity. High arsenic levels also induce oxidative stress which, in addition to elevating insulin resistance, induces beta cell dysfunction through activation of nuclear factor kappa B (NF-kappaB). Furthermore, superoxide by interacting with uncoupling protein 2 (UCP₂) can cause amyloid formation in the pancreas, which over time will destroy the insulin-secreting beta cells.[12]

Therefore, the association of a high white rice intake with diabetes could be due to excessive intake of a high glycemic index carbohydrate and/or to a high intake of arsenic. Studies of replacement of white rice with another cereal with a low arsenic content need to be preformed. If these studies showed decreased arsenic levels and that the lower arsenic levels are associated with a decreased incidence of diabetes, then efforts to decrease rice intake especially in Asia should be undertaken.

Declaration of interest

DSH Bell has been a consultant and speaker for Novo Nordisk, Janssen and Takeda. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

David SH Bell

Southside Endocrinology and University of Alabama at Birmingham, Birmingham, AL, USA

Correspondence: David SH Bell, 3928 Montclair Rd. Suite 130, Mountain Brook, AL 35213, USA. E-mail: [email protected]