Do sugary drinks cause obesity and diabetes?: How financial conflicts of interest determine the answer

Seems like a pretty straightforward question, right?

Unfortunately, nothing about nutrition science is straightforward. That especially means research, which is flooded with massive amounts of industry funding each year. I’ve already written about the hundreds of millions of dollars Coca-Cola and PepsiCo pour into public health each year. But is this a bad thing?

From one perspective, not at all. Public health (including research) is outrageously underfunded. For example, a recent analysis of National Institutes of Health funding found that less than 10% of NIH’s roughly $30 billion annual budget supports human behavioral interventions to prevent chronic diseases. And if we’re going to make any kind of significant inroads curtailing the $47 trillion global economic price tag of chronic diseases, it’s going to take significant additional investments to supplement government’s modest current efforts. (In this case, I’m not just talking about the US Government, but governments globally.) So, following this line of reasoning, and from a pure dollars and cents perspective, industry can be a significant funding source for public health, including research, regardless of differing fundamental interests. Likewise though, this line of reasoning also, and more dangerously assumes that where funding comes from has no influence, whether explicitly or implicitly, on subsequent human behavior/actions (research, policy, programs, or otherwise).

There in lies the big catch. However immune people think they are from being swayed by even small gifts, study after study continues to show this isn’t the case. As Tavris and Aronson describe in their book (and one of my favorite books of all time) on cognitive dissonance entitled, Mistakes were make (but not by me), “…being given a gift evokes an explicit desire to reciprocate.” In healthcare, for example, even seemingly benign industry meals costing $20 subsequently altered physician prescribing practices (I wrote about this is more detail in a previous post). And contrary to popular logic, small gifts actually have been found to influence behavior more than large ones.

Yet physicians, researchers, and others who receive industry funding still believe it won’t bias the results. We repeatedly see the opposite in healthcare, public health, and nutrition research. Here are just a couple examples.

  • This 2016 review on the effects of artificially sweetened beverages on weight found that 75% of industry-funded studies produced favorable results.
  • This 2013 review on the association between sugary drink consumption and weight gain or obesity found that industry-funded studies were 5 times more likely to produce a favorable conclusion compared to non-industry funded studies.
  • This 2014 review of studies that analyzed the use of neuraminidase inhibitors in the prophylaxis or treatment of influenza found 88% of studies with a financial conflict of interest produced a favorable result compared to 17% of studies without a conflict.

We can add another to this list.

A few days ago, the Annals of Internal Medicine published a review of experimental studies that found no association between sugary drink consumption and obesity- and diabetes-related outcomes and their funding source. In essence, researchers were looking at studies from January 2001 through July 2016 that were funded by industry and whether these studies were more likely to conclude “no association” between sugary drinks and obesity and type 2 diabetes compared to studies funded by non-industry sources.

Here’s the main finding:

Of the 60 studies analyzed, 26 out of the 26 papers that failed to find a link between sugary drinks and obesity or type 2 diabetes were funded by industry sources. 

Yes, that’s 100%.

So when it comes to evaluating nutrition research outcomes, we should remember this advice from one of the study authors,

It’s important to know the source of the message and who paid the messenger.

I couldn’t agree more. As I wrote about before, it’s about the person holding the megaphone.

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