Musings: What color is your rice? Rice, diabetes, and arsenic.

This is a supplementary page, for What color is your rice? Rice, diabetes, and arsenic. (December 12, 2010).

Continued...


What are brown and white rice?

White rice is the most highly milled form of rice. It is mainly the endosperm -- starch granules; all the outer layers have been removed. Brown rice is a less-milled form of rice; it retains a bran layer surrounding the starch.

As a generality, nutritionists will say that the nutritional value of grains is reduced by milling. In the context of rice, the highly milled white rice has little nutritional value except calories (from the starch). Brown rice contains more protein and minerals.

White rice is more popular -- as is common with refined grains. Why? Habit probably plays a big role in this. But one point that was brought up is likely also important historically. Brown rice does not store well. It contains polyunsaturated fats, and easily goes rancid upon storage. (Note that its poor storage is due to a feature that is otherwise good for you nutritionally.) Thus the traditional practice of storing the rice harvest, perhaps for a year, is practical only with the more refined white rice.

Are appearance or taste relevant to the appeal of one kind of rice or another? I doubt these are major issues. Perhaps the whiteness of white rice appeals to some as cleaner -- even though in some ways it means exactly the opposite (it is less nutritious). Brown rice is tastier than white rice. However, rice (and other extreme starch sources) tend to be incorporated into dishes where other things provide taste. With brown rice, one can actually imagine eating it on its own merit.


Rice and diabetes

What got the topic started is a paper reporting that rice consumption is correlated with diabetes incidence. More specifically, greater consumption of common white rice is correlated with increasing levels of Type 2 diabetes. On the other hand, greater consumption of brown rice is correlated with decreasing levels of Type 2 diabetes.

It is hard to present brief examples of the results, since they are presented in quite complex tables, with inconsistent format. As a simple but certainly not adequate summary... The measure they use is relative risk (RR). An RR value of 1 means that the condition has no effect, a value above 1 means there is a positive effect (greater risk), and a value below 1 means a negative effect (less risk). For brown rice, all of the various RR values they present -- for various consumption levels and calculation models -- are below 1, indicating that brown rice consumption is associated with a lower risk of Type 2 diabetes. In contrast, for white rice, 3/4 of the RR values are above 1.

The work is entirely epidemiological, based on analysis of existing large data sets for health. The good news is that lots of data are available; the bad news is that it is unclear what it all means. It is inherent to such epidemiological studies that they cannot show causality, only correlation. As an example of a type of concern about such correlations... it may be that people who eat brown rice have some other relevant "good" habit, which has not been identified. (They do attempt to control for many variables that occur to them.)

I probably would not have given the item much attention, except that it did note that other studies showed similar effects in Asian populations with high rice consumption. Further, there are other data to support that whole grains tend to lower diabetes; some of these data, from the same studies, are discussed. So I think we should have some respect for this work. They show a relationship, though it is not clear what it means. The paper provoked thought, and led me to look for related information. And that led to the point in the next section.


Links for this section...

Press release: Type of Rice Linked to Diabetes Risk. (NIH, June 28, 2010.)

The article, which may be freely available: White Rice, Brown Rice, and Risk of Type 2 Diabetes in US Men and Women. (Q Sun et al, Archives of Internal Medicine. 170:961, June 14, 2010.)


Rice and arsenic

One issue that came up is that rice plants accumulate arsenic. Levels of As are higher in rice than in other grains. Further, the level of rice is higher in the bran (the outer, brown layer) than in the endosperm (inner, white layer). It is interesting that the bran, known for containing more of good minerals, may also contain more of bad ones.

The work suggests that in areas of extremely high rice consumption, where rice may be more than 50% of the caloric input, eating high-As rice may contribute to an increased level of cancer. Further, brown rice is worse, though the difference is small. (The As level of the bran is much higher than in the endosperm, but the amount of bran in brown rice is small enough that the effect on overall As input from rice is small. However, direct consumption of rice bran may be a more serious issue.)

There are reservations about this kind of work. Importantly, are the data reported here representative of the product? Further, what is the alternative? If rice is contributing As to the diet, eating less rice would reduce As consumption. But eating less rice must be compensated by eating more of something else. Although they do note that rice tends to be higher in As than other grains, it is not clear that would apply to other grains grown in the same area. All these objections can be addressed. The work at least raises the concern that the As content of rice may be a problem -- a problem worth looking at further. It may be most important for those who consume rice bran as a distinct product.


Two papers on this topic, from the same people:
* Inorganic Arsenic in Rice Bran and Its Products Are an Order of Magnitude Higher than in Bulk Grain. (G-X Sun et al, Environmental Science and Technology 42:7542, October 1, 2008.)
* Geographical Variation in Total and Inorganic Arsenic Content of Polished (White) Rice. (A A Meharg et al, Environmental Science and Technology 43:1612, March 1, 2009.)


Implications

We have presented some scientific papers about possible medical effects of rice -- beyond the nutritional basics. The papers present some facts, perhaps preliminary facts in some cases, and some interpretations. Inevitably, one wonders what we are supposed to do with this information. The papers may seem to say that white rice is bad because it leads to diabetes, and brown rice causes arsenic poisoning. Slow down! Those are over-reactions to what was presented. One person during our discussions even suggested that we ignore most of this, at least for now, and just emphasize eating a diverse diet of mostly good foods. That is actually a pretty good idea.

The work presented here is incomplete. Maybe it has health implications of importance, maybe not. Further work can sort that out.

For example, the work that started this topic reported a correlation between white rice and diabetes. Interesting, but a fairly small effect. And the reason for the correlation is not known.

The As work has many complications. Simply knowing the As level in the rice is incomplete information. Among the complications they discuss...
* What is the form of the As in the rice. Some chemical forms of As are more hazardous than others.
* How "available" (bio-available) is the As? Some chemicals in our food may not end up in our body, because we do not absorb them. (This is a major issue with iron.)
* What is the effect of cooking on the As level. They discuss this some, and note that it may vary depending on the nature of the cooking.


General resources

Origin, dispersal, cultivation and variation of rice. (G S Khush, Plant Molecular Biology 35:25, 1997.) There is also a freely available copy at pdf copy. A readable overview of rice history, from a scientist at IRRI -- the International Rice Research Institute, in Manila.

Khush's article (above, p 26) contains a table on rice production by country or region, for 1995. For some more complete and more recent data: see World Wheat, Corn, and Rice Production, 2003 (Courtesy FAO). Scroll down a bit, to the big table. It is for three crops; rice is at the right. And it includes data by country for all countries. As with Khush's table, data are shown for amount of land devoted to the crop (in hectares), amount produced (metric tonnes), and then productivity (Mt/ha). The table is sorted by amount produced. Comparing the 2003 data here with Khush's data for 1995... The major producers are about the same; the only change in the top ten producing countries is that Brazil, the #1 rice producing country outside Asia, has sneaked above Japan into 9th place.

On a local note... The US is not a major rice producing country -- ranking 11th in amount produced. However, within the US, California is one of the major rice-producing states -- 2nd, in fact, accounting for about 20% of US rice production. It is the only major rice-producing state outside of the "deep south". California rice production is largely in the Sacramento Valley, 100 miles or so northeast of here. Interestingly, rice production in California is among the most productive in the world, at over 9 tonnes/hectare (p 7). This is the highest in the US, and is higher than that of any country except Egypt. California rice production is high-tech: "Nearly 100 percent of these flatlands have been further leveled by laser-directed machinery. In rice monocrop systems, the land may be leveled to a slope of 0.02 to 0.05m/100m." (p 3) [Page references are to California Rice Statistics and related National and International Data. (California Rice Commission, 2009.)]

Rice. (Te-Tzu Chang, The Cambridge World History of Food. 2000.) Another overview; seems like a high quality encyclopedia-type article.

* * * * *

Thanks to several people for helpful discussions -- and resources. We had considerable email exchange on various aspects of this topic; the input was helpful for both broad perspective as well as specific information. I have not used everything that was sent to me, but tried to distill the material into a relatively concise post that offered several issues and views, though certainly not all. If you think I missed something important -- or interesting -- drop me a note; we can add an addendum to this page.



Return to this item on main page: What color is your rice? Rice, diabetes, and arsenic. (December 12, 2010).

Follow-up posts:
* Rice and arsenic: a follow-up (January 8, 2012).
* Rice and arsenic: rice syrup, baby food, and energy bars (April 23, 2012).
* The rice-arsenic issue: Consumer Reports and the FDA weigh in (September 25, 2012).

A post that refers to the "General resources" listed above: Can growing rice help keep you from becoming WEIRD? (July 22, 2014).


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