1 October 2013

Food for Thought

Sugar, diabetes and why the state of our health is not about any one thing. 
Many of the nutrition studies we share with GI News readers are prospective studies. Looking at large groups of people over a period of time (usually many years), the researchers mine the data (rather like gold prospectors) looking for links between diet (e.g., consumption of fruit or vegetables or red meat or whole grains or sugar) and health. What you need to remember when you read (or watch) headline-hitting health stories featuring research findings from such studies is that the correlations or associations they find don’t actually establish causation. Prof David Katz comments on a recent study in Plos One using econometric models of repeated cross-sectional data of the association between sugar intake and diabetes around the world. Here is an edited summary of his Huffington Post piece reproduced with permission. 

Dr David Katz
Dr. David Katz

‘The study itself, published in the journal Plos One, is excellent overall. This kind of ecological evaluation – looking at an association between X and Y at the population level is certainly of some value. But it is absolutely not the “closest thing to causation” – in fact, it is among the least reliable forms of evidence. At the population level, the presence of a Bentley in the driveway, or a high-speed Internet connection in the home, is profoundly associated with reduced likelihood of malaria (or tuberculosis, or leprosy, etc.). This is absolutely not because Bentleys or the Internet protect against leprosy or malaria. Rather, affluent people with expensive cars and high-speed Internet access are much less likely to encounter malaria or leprosy than the poor for reasons having nothing to do with horsepower, or bandwidth.

Fundamentally, Dr Basu’s team found that the greater the availability of daily calories from sugar around the world, the more diabetes. I’m having some trouble figuring out what is supposed to be surprising about this. If people add sugar calories to their diets, they are getting both more sugar, and more calories, and those exposures alone and together are well known to contribute to diabetes risk. If they are adding sugar calories in place of other calories, then the percentage of total daily calories coming from sugar is going up, and the overall quality of diet is going down. Again, this pattern is pretty well linked to diabetes risk (and other chronic disease risk, for that matter) already.

To some extent, the Basu study was a self-fulfilling prophecy. It’s true the researchers looked at other associations between diet and diabetes. But consider that one food category was “meat,” which presumably lumped together everything from salmon to salami. Some such “meats” likely defend against diabetes, while others would likely increase risk. Lumped together, nothing much would be visible. Similarly, there was a category of “cereals,” but with no distinction between whole grains and refined starch. Putting everything from steel-cut oats to Cap’n Crunch in one category would not facilitate keen insights. The authors did not look at nuts and seeds, despite numerous studies – including one just published in the Journal of Nutrition – demonstrating that higher intake of walnuts and other nuts is associated with reduced diabetes risk.

Since Dr Basu’s methods involved looking at sugar dose available in the food supply per person per day, and the prevalence of diabetes in the population, there is nothing in the data to prove that those who ate the most sugar were most likely to develop diabetes – although one may infer that. Rather, as countries make more sugar calories available each day (i.e., become more like the US), their populations have more diabetes. Again, this is not terribly surprising.

But it’s more than a little wrong to conclude that since sugar intake contributes to diabetes risk, nothing else matters. In fact, Dr Basu and colleagues state explicitly that increasing sugar availability accounts for roughly one-quarter of the global rise in diabetes rates between 2000 and 2010. This clearly implies that something other than sugar accounts for almost 75 percent of that increase.

The reality, alas, is that the state of our health is not about any one thing. We can cut fat, and get fatter and sicker – by eating more starchy, sugary junk. We can cut carbs by switching from beans to baloney, and get fatter and sicker. And we can cut sugar and consume ever more artificially-sweetened, starchy, fatty junk – and get fatter and sicker. We clearly like little bits of truth we find easy to digest. But none of these is the whole truth, and when bits of truth are mistaken for the whole – they might just as well be falsehoods.’

About Dr David Katz
Known internationally for expertise in nutrition, weight management, and chronic disease prevention, Katz is the founding director of Yale University's Prevention Research Center. He is the founder and President of the non-profit Turn the Tide Foundation, and a blogger/medical review board member for The Huffington Post.