You can read about the National Institutes of Health sponsored study that led up to these findings in the 14 June online issue of the journal Archives of Internal Medicine. The lead author was Dr Qi Sun who worked on the study while at Harvard School of Public Health (HSPH) and is now an an instructor of medicine at Brigham and Women's Hospital, both in Boston, Massachusetts.
Sun, whose work was supported by a postdoctoral fellowship from Unilever Corporate Research, told the press that this was the first study to compare links between white and brown rice consumption and diabetes risk among Americans, who are eating a lot more rice now than they did a few decades ago.
"We believe replacing white rice and other refined grains with whole grains, including brown rice, would help lower the risk of type 2 diabetes," said Sun.
He and his colleagues found that consuming five or more servings of white rice a week was linked to an increased risk, yet eating two or more servings of brown rice was linked to a lower risk, of developing type 2 diabetes.
They estimated that replacing a small amount (50 gm, or about one third of a daily serving) of white rice with brown rice would be enough to lower the risk by 16 per cent, and doing the same with whole grains like wheat and barley would lower it even more, by 36 per cent.
For the study they examined data on 157,463 women and 39,765 men from the Health Professionals Follow-up Study (HFPS) and the Brigham and Women's Hospital-based Nurses' Health Study (NHS) I and II. The data came from questionnaires given out every four years where the participants answered questions about their lifestyle, diet, health conditions and medical status.
The results showed that:
- During 22 years of follow up in the NHS 1 study, there were 5,500 documented cases of type 2 diabetes among the participants, while over 14 years there were 2,359 cases among NHS II participants, and over 20 years there were 2,648 among the HFPS participants.
- After adjusting for age and other lifestyle and dietary risk factors, consuming 5 or more servings per week of white rice was linked to a higher risk of type 2 diabetes compared with consuming less than one a month (pooled relative risk was 1.17 with 95 per cent confidence interval CI ranging from 1.02 to 1.36).
- In contrast, consuming 2 or more servings of brown rice per week was linked to a lower risk of type 2 diabetes compared with consuming less than one a month (pooled relative risk 0.89, with 95% CI from 0.81 to 0.97).
- Replacing 50 grams (uncooked, about one third of a daily serving) of white rice with same amount of brown rice was linked to a 16 per cent lower risk of type 2 diabetes (95 per cent CI from 9 to 21 per cent).
- The same replacement with whole grains as a group was linked with a 36 per cent lower risk of type 2 diabetes (95 per cent CI from 30 to 42 per cent).
"Substitution of whole grains, including brown rice, for white rice may lower risk of type 2 diabetes."
They suggested the findings support the idea that to prevent developing type 2 diabetes, most of our carbohydrate intake should come from whole rather than refined grains.
White rice is the result of milling and polishing brown rice, which strips away the fiber and most of the minerals and nutrients in the grain, making it easier and quicker to digest so the main end product, sugar, enters the bloodstream faster. This is also the case for other grains that we eat, like wheat and barley.
The researchers also found that the biggest consumers of white rice were more likely to have a family history of diabetes, but less likely to smoke or be of European descent.
In contrast, there was no particular ethnicity link for brown rice consumption: instead, people with a health conscious lifestyle and diet were the most likely to eat brown rice.
After ruling out potential influencers like age, body mass index (BMI), alcohol, smoking, family history of diabetes and other dietary factors, the links between white rice consumption and increased risk of diabetes was still there.
When they did a secondary analysis that included only white participants, thus ruling out the effect of ethnicity on both white rice consumption and diabetes risk, they found much the same result.
There were much fewer participants eating brown rice in the sample compared to eating other whole grains, and this could account for the researchers not being able to determine if higher levels of brown rice consumption might link with even lower risk of diabetes; it might also explain why eating more whole grains overall was more reliably linked to lower risk of the disease than the figures for brown rice would indicate.
The US government's guidelines suggest that Americans should get at least half of their carbohydrates from grains, including rice. But although Americans are eating more rice, it's mostly white rice. Senior author Dr Frank Hu, professor of nutrition and epidemiology at HSPH, said:
"From a public health point of view, whole grains, rather than refined carbohydrates, such as white rice, should be recommended as the primary source of carbohydrates for the US population."
He said their findings could have "even greater implications for Asian and other populations in which rice is a staple food".
"White Rice, Brown Rice, and Risk of Type 2 Diabetes in US Men and Women."
Qi Sun, Donna Spiegelman, Rob M. van Dam, Michelle D. Holmes, Vasanti S. Malik, Walter C. Willett, Frank B. Hu.
Arch Intern Med., Vol. 170 No. 11, 961-969 published online 14 June 2010.
Written by: Catharine Paddock, PhD