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Soda, Diabetes Linked by Scientific Misconduct?

If you doubt that our society's lifestyle nannies are of dubious integrity, a new highly publicized study supposedly linking regular (non-diet) sodas with weight gain and diabetes should clear up any remaining skepticism. 

“The message is: Anyone who cares about their health or the health of their family would not consume these beverages. Parents who care about their children’s health should not keep them at home,” study author Walter Willett of Harvard University told The Washington Post. 

In a nutshell, Willett and his co-authors would have us regard Coca-Cola in the same way as they would have us regard Marlboro cigarettes — that is, no level of soda consumption is safe. 

The study data collected from 51,603 women reportedly show that the 1,007 women who increased their consumption of regular soft drinks over a period of four years from less than one per week to one or more per day gained an average of 10.3 pounds. Among the approximately 16,600 women who consumed more than one soft drink per day, the researchers reported 83 percent more cases of type 2 diabetes (search). 

The researchers would have us believe their results indicate that soda by itself causes weight gain and diabetes. But this conflicts with existing data and common sense. The National Academy of Sciences’ Institute of Medicine issued a report in 2002 titled “Dietary Reference Intakes on Macronutrients” that stated, “there is no clear and consistent association between increased intake of added sugars and [weight].” A single new study doesn’t change that fact. 

Next, since the consumption of one 12-ounce soda per day (150 calories) for four years amounts to 219,000 calories — or a minimum of 62.5 pounds of added bodyweight at 3,500 calories per pound of body fat — it’s obvious that the women’s reported weight gain of 10.3 pounds is somewhat more complex than the simple-minded notion that the soda went straight to their hips and thighs. The real explanation for the reported weight gain more likely lies in the women’s genetics and their overall lifestyles. 

Moreover, the study reports that women who consistently drank one or more regular soft drinks per day during those four years actually gained slightly less weight than women who consistently drank less than one soda per week during that same period. 

The researchers’ contention that soda intake is linked with type 2 diabetes is also not borne out by their data or anyone else’s. The media-spotlighted claim of an 83 percent increase in diabetes among consumers of more than one soda per day — itself an inherently weak association from a statistical perspective — is misleading.  

When the researchers statistically adjusted their results for bodyweight (a risk factor for diabetes) and for caloric intake (a proxy measure for consumption of sweetened foods other than soda), the 83 percent increase dropped to an even more statistically dubious (and soft-pedaled) 32 percent increase. That result is of the same magnitude as the study’s reported 21 percent increase in diabetes among consumers of more than one diet soft drink per day. Diet drinks, of course, do not contain any sugar at all.

I also discovered what I consider to be a flagrant and inexcusable omission on the part of the researchers. A recent study of 39,876 women entitled “A Prospective Study of Sugar Intake and Risk of Type 2 Diabetes in Women” (Diabetes Care, April 2003) concluded that sugar intake was not associated with the risk of type 2 diabetes and that “these data support the recent American Diabetes Association’s guideline that a moderate amount of sugar can be incorporated into a healthy diet.” 

Certainly Willett and his co-authors could claim it was mere oversight on their part to not even mention this major conflicting study in the write-up of their study, but that assertion would be on thin ice given that Harvard Medical School’s JoAnn Manson was a co-author of both studies! 

When I asked Manson how she reconciled the conflicting results, she reached for her media-training skills and tried deflecting me with congratulations for discovering the April 2003 study and for being the first media person to ask her that “great” question. She then told me that what really made the new study compelling was that it measured the health impact of a change in soft drink consumption. That still did not answer my question.  

Her new study only presented data concerning a potential association between increasing soft drink consumption and weight gain. It presented no data on increasing soft drink consumption and diabetes. The omission of even a mention of her own extremely relevant and contradictory April 2003 study in the new study’s write-up — let alone an effort to reconcile the differences between the studies — is in my opinion an egregious one on the part of Manson and her co-authors. 

Given that both studies were funded with taxpayer dollars (grants from the National Institutes of Health), I’d like to see an investigation by the federal Office of Research Integrity.  

Researchers should be accountable for misusing taxpayer dollars to irresponsibly portray half-truths as scientific gospel, especially when such misconduct scares the public and harms legitimate businesses.

Steven Milloy is the publisher of JunkScience.com, an adjunct scholar at the Cato Institute and the author of "Junk Science Judo: Self-Defense Against Health Scares and Scams" (Cato Institute, 2001).

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