“White rice could cause diabetes” The Independent UK
“White rice link seen with type II diabetes” Yahoo News
“White rice raises T2 diabetes risk” The Telegraph
Those were the headlines of the last few days. Of the three posted, one is really wrong, one is sort of OK, one is almost OK and all are meaningless. The headlines come out of a “meta-analysis” of population studies of risks associated with diabetes. Meta-analysis are important because they consider the quality of studies and combine their results which, if done well, reduces the chance of giving erroneous results. In this case there were only four studies included in the meta-analysis. The paper was published in the British Medical Journal and is available here if anyone wants to read it.
So – the real question, is “can we keep eating rice?” The overwhelming answer is “yes we can!”
To answer why, you may need to learn something about (in a whisper) statistics. If you are new to reading medical journals then one of the terms you will run across and need to understand is “Relative Risk.” What the number means is the increase in risk (chance of having the disease) of one group compared to another. A Relative Risk of 1.5, then, means that one group is 1.5 times as likely to get the disease as another. Right away, you can see that it is easy to get a high relative risk by comparing groups with very low absolute risk to those with high absolute risk. Eg, for Type 2 diabetes if we compared healthy normal weight individuals with obese individuals then the relative risk would be high for the obese individuals. In this meta-analysis they compared the group with the lowest consumption of rice with those with the highest consumption of rice. Before I give the numbers, remember that most people do not have either the lowest or the highest consumption, but somewhere in between. Anyway, for Western populations the relative risk was 1.12 and for Asian populations it was 1.55. This looks like those Westerners eating heaps of rice are about 12% more likely to get Type 2 diabetes than those eating the least. However, the devil is in the details…
Stats lesson number 2. The 1.12 is presented with some numbers after it in brackets: 1.12 (0.94 to 1.33). These numbers are crucial. They are even more important than the 1.12 itself! They are what is called a confidence interval. In this case a 95% confidence interval. They are an indication of just how good the estimate of 1.12 really is. In this case, not very good. The authors are saying that they are 95% confident that the true relative risk (i.e. the number we would get if we included everyone in the world in the study) is somewhere between 0.94 and 1.33. Because this number straddles 1 there is a good chance (maybe ~25%) that the real relative risk is actually less than 1, in other words that eating the least amount of rice has a greater risk than eating the most! In the Asian population the relative risk was 1.55 (1.20 to 2.01) which suggests that it is unlikely that the real relative risk is less than 1.20.
OK then, let us for a minute assume that if we measured everyone in the world and found a true relative risk of 1.2 for those eating the most rice compared with those in the group eating the least. What does that mean to you and me. Probably nothing, because what is important is Absolute risk. As far as Type II diabetes goes the equation is simple – if you are obese then you are at high absolute risk of Type II diabetes. Eating rice is going to make next to no difference. If you eat heaps of rice it is probably because you eat heaps of food. Cut back on the rice, but for goodness sake do not replace it with pasta or spuds or anything else for that matter. If you eat well and exercise a bit and happen to prefer rice to spuds….then there is no big deal…bon appetite.