*From Deltoid archives for 2004, a [repost](http://scienceblogs.com/deltoid/2004/09/zywicki.php)*
Higher consumption of sugar-sweetened beverages is associated with a greater magnitude of weight gain and an increased risk for development of type 2 diabetes in women, possibly by providing excessive calories and large amounts of rapidly absorbable sugars.
Todd Zywicki, who endorsed Milloy’s piece as a “devastating critique” has mounted a defence of Milloy. Unfortunately it is clear that Zywicki has not read the article (subscription required) or even the abstract describing the study.
Zywicki dismisses concerns about Milloy’s character raised by Davies and John Quiggin as not relevant to the question of whether the JAMA study is a good one or not. It isn’t, but Zywicki hasn’t read the JAMA study. Instead he is relying on Milloy to accurately describe it. Milloy’s character suggests that his description of the study might be misleading; and in fact it is misleading and as we will see below, Zywicki has been mislead.
Milloy says that the once the researchers “statistically adjusted their results for bodyweight (a risk factor for diabetes) and for caloric intake (a proxy measure of consumption of sweetened foods other than soda), the 83 percent increase [in type 2 diabetes prevalence] dropped to an even more statistically dubious (and soft-pedaled) 32 percent increase.” Now it seems to me that Milloy is obviously correct here—bodyweight and non-soda caloric intake seem to me to obviously relevant to trying to isolate the marginal effect of the increased soda consumption. So the 83 percent figure is really an irrelevant number
Milloy has mislead Zywicki into thinking that the 83% increase in diabetes was partly caused by confounds—that the women who drank more sugary drinks also happened to be heavier and eat more and that these factors are what caused most of the increase. But right in the abstract they clearly state (my emphasis):
After adjustment for potential confounders, women consuming 1 or more sugar-sweetened soft drinks per day had a relative risk [RR] of type 2 diabetes of 1.83 (95% confidence interval [CI], 1.42-2.36; P<.001 for trend) compared with those who consumed less than 1 of these beverages per month.
So what is the 32% figure that Milloy tried to pass off as the “real” increase? Well, they found that increased soda consumption was associated with weight gain and weight gain is known to be a risk factor for diabetes. The 32% increase is the extra risk factor for soda consumption on top of the increase from the weight gain from drinking more soda. It would only be the real risk if sugar-sweetened drinks did not cause weight gain, but they do.
This is not the only matter that Milloy has misled Zywicki about. Zywicki writes:
Milloy similarly notes that the study does not control for genetics or lifestyle issues
But the study did control for genetics and lifestyle issues (my emphasis):
We evaluated whether the association between sugar-sweetened soft drink consumption and risk of diabetes was modified by BMI, physical activity, and a family history of diabetes using analyses stratified by these variables and by modelling interaction terms.
Milloy even accuses the authors of “scientific misconduct” for not mentioning another study that Milloy alleges contradicts their results. But that other study was not about soft drink consumption but about overall sugar consumption. The new study suggests that consuming sugar in a drink where it is more rapidly absorbed may increase the risk of diabetes. This is hardly contradicted by results that suggest that sugar intake including that in solid food is not a risk factor. Zywicki endorses the serious charges that Milloy makes without checking whether they are accurate.
Update: The Washington Times has also published Milloy’s misleading article and Reason‘s Nick Gillespie was also taken in. Matthew Yglesias reckons that libertarians should just argue that they have a right to unhealthy food instead of trying to debunk the science that shows them to be unhealthy.
Update 2: Nick Gillespie links here (thanks!) and to a Tech Central Station article by Jon Robison that criticizes the JAMA study. Robison, like Milloy, tries to pass of the 32% increase in diabetes, which is the extra risk after accounting for the effect of weight gain, as the total increase in risk. Robison also asserts that “Epidemiologists generally agree that relative risks less than 2 should be ignored or at least viewed with extreme skepticism”. In fact, epidemiologists do not “generally agree” with this. I explain why in this post.