We like explanations that are simple, easy to understand, and explain everything. One example of this is the idea that eating carbohydrate, or sugar, is the primary cause of obesity. This lets us point our finger at something concrete and change our behavior accordingly. And it's true enough that it has practical value. But the world around us often turns out to be more complex than we'd like it to be.
The CDC recently released its latest data on the prevalence of obesity in the US, spanning the years 2013-2014 (1). These data come from its periodic National Health and Nutrition Examination Surveys (NHANES). Contrary to what many of us had hoped for after a slight decline in obesity in the last survey, the prevalence has once again increased. Today, roughly 38 percent of US adults have obesity. As a nation, we're continuing to gain fat, which is extremely concerning.
I decided to examine the relationship between obesity prevalence and our intake of carbohydrate and sugar over the years. The food intake data come from the USDA's Economic Research Service (2). For some reason, the data on carbohydrate don't extend beyond 2010. This probably relates to funding cuts at the USDA*.
Let's have a look at the data for carbohydrate:
Carbohydrate intake peaked in 1999, and has apparently been declining since then. Yet obesity is still rising.
For our sugar intake, the data extend to 2013, so we get a longer, more informative picture (added sugars):
The relationship is even clearer here. Our sugar intake has been declining since 1999, and is now back to where it was in the late 1980s. Yet our waistlines keep expanding.
Refined carbohydrate and sugar are certainly part of the cause of the obesity epidemic, but these data are consistent with a large body of research suggesting that there's more to the story. Obesity is caused by a number of interacting diet and lifestyle factors, most of which can be traced back to major socioeconomic changes in this country over the last century. These have affected the way we interact with food, the composition of our food, and other aspects of our lifestyle that cause genetically susceptible people to gain fat.
* Which leaves us with a record of US dietary intake that ends somewhere between 2010 and 2013. In my view, this is a serious threat to public health research.