Some connections are just so obvious we hardly give them a second thought: drinking and driving, crack and bad teeth, smoking and lung cancer. And — this week's topic — soft drinks and weight gain. The logic is so right there — you put on weight when calories going in exceed calories going out, and sugar-sweetened beverages (SSBs) are loaded with calories. You'd think no scientist could seriously claim "insufficient evidence" for a causal relationship.
You'd be wrong. You can find seven "systemic reviews" (meta-studies) online which conclude that the evidence for an SSB-and-weight-gain connection is either contradictory or insufficient. However, you can also find 10 opposing studies showing that consumption of SSBs does increase the risk of weight gain and obesity. Why the contradictory results? Who do you trust? In a "meta-meta review" (PLOS Medicine, December 2013), researcher Maria Bes-Rastrollo and her collaborators took a close look at all these studies (with 18 conclusions), all of which had been published in mainstream scientific journals. The results are both enlightening and depressing, especially for those of us who love science and idealize the supposed neutrality of the scientific method.
Turns out, six of the studies disclosed a conflict of interest (they were funded by the soft drink industry), five of which (83.3 percent) came down on the "insufficient evidence" side of the issue. Meanwhile, of 12 conclusions from the other 11 studies, 10 (again, 83.3 percent) said there was sufficient evidence for the connection, repudiating the industry-funded reviews. The conflict-of-interest reviews were five times as likely to conclude there was no proven SSB-weight gain connection compared with those not paid for by the industry.
Cynical readers may ask, what else is new? Scientists can be bought — or, to put it more kindly, influenced — by the source of their funding. Tobacco companies, for instance, can always find some desperate Ph.D. willing to challenge the cigarette-lung cancer connection. And researchers, being human, have their biases, too. That's why most studies of this type use double-blind protocols, and why reputable journals insist on peer review as a condition of publication. Still, the very nature of scientific research, at least in my view, is that scientists don't skew results to fit their prejudices.
Compare this situation with the immoderate claims often made by the sports drink industry that "maximum hydration" — drinking as much Gatorade and suchlike as your body can tolerate — is better for athletes than simply drinking when they're thirsty. That's just aggressive advertising with no harmful consequences. But it's another state of affairs when supposedly neutral scientists play to their sponsors, as happened so blatantly in the SSB-obesity case.
What's particularly galling is that here in the country with the second highest obesity rate in the world (after Mexico), where a full third of us are obese, purveyors of calorie-rich soft drinks can point to the skewed industry-sponsored results with impunity. Truth is, SSBs are the single largest source of added sugar in the U.S. diet, and the only place those excess calories can go is into your body: Hello tummy, goodbye visible toes.
Barry Evans (firstname.lastname@example.org) still yearns for dandelion-and-burdock, his British childhood "fizzy drink" of choice.