Monday, October 20, 2014

What's the story behind the calories + activity labels for soda?

Another study meant to test the effect of providing nutrition information at the point of sale has been published in a respected peer reviewed journal.  In addition, the results of the study are reported in the popular press and as often occurs, the popular press is reporting selectively.  It’s unfortunate that reporters would be selective or misrepresentative because the actual findings are impressive without embellishment or obfuscation. 

Here it is in a nutshell.  In 2012/2013, Sara Bleich and colleagues Barry, Gary-Webb and Herring conducted a study in Baltimore, MD. They introduced 4 beverage related nutrition disclosures (or treatments) to a small sample (n=6) of corner stores that were in walking distance to nearby middle and high schools. All 6 stores received each of the 4 nutrition treatments for about two weeks– but in random order.  The nutrition disclosures, which were placed on signs on beverage cases were 1) Did you know that a bottle of soda or fruit juice has about 250 calories? Or 2) Did you know that a bottle of soda or fruit juice has about 16 teaspoons of sugar? Or 3) Did you know that working off a bottle of soda or fruit juice takes about 50 minutes of running? Or, 4) Did you know that working off a bottle of soda or fruit juice takes about 5 miles of walking?  [Note that the exercise examples are not equivalent, a flaw the researchers note in the limitations section of their paper.  Why does it matter?  People may not know how long it takes them to walk five miles, for me it would be more than 90 minutes.  In addition, the calorie expenditure data was based on a male or female adolescent weighing about 110 pounds.  The individualistic nature of calorie expenditure is one of the reasons I prefer multiple traffic light labels over exercise equivalents for an informative information disclosure.]  While the nutrition treatments were in place (i.e., the randomly selected sign was posted) research assistants collected sales receipts from a random sample of purchases at each store.  To be included in the random sample, the sales receipt had to be associated with someone who appeared to be between the ages of 12 and 18 and black.  This is important because the results of the study are generalizable to black adolescents in a Northeastern US city – not other kids, not adults, not other types of locations(e.g., a rural town).  The headlines in popular press do not make this distinction and only focus on one thing.  The headlines promulgate the findings that telling a person how much activity they will have to do to burn the calories in a soda or fruit juice leads to a change in the number of sugar sweetened beverages purchased, the size of sugar sweetened beverages purchased, and the average number of calories purchased. 

In the study, (see table 1 if you can access it) the average beverage calories sold when no information was posted was 207; the average calories sold during the calorie only treatment was 185; the teaspoons of sugar treatment, 188; the minutes of running treatment, 193; the minutes of walking treatment, 187.  In this analysis, for this outcome, the best treatment was the calorie only disclosure.  The average percent of sugar sweetened beverages purchased when no information was posted was 97%; for all of the different treatments the percent of sugar sweetened beverages purchased was between 88.3% and 89.1% - more than a 10% drop from the no information treatment, but similar across information types.  The purchase of sugar sweetened beverages greater than 16 ounces (recallthis post about the portion size cap) was around 53% when no information was posted and a much lower 38% with the calorie only treatment, 42.7% with the teaspoons of sugar treatment and 46.7% and 47.9% with the running and walking treatments, respectively.  As you can see, there is no earth shattering headline about exercise equivalents in the overall results of this study and in fact, the results are an exception to previous findings that calorie disclosures alone did not work.  However, in the analysis I just described, the types of disclosure or treatments were not directly compared to each other. 

In a sub analyses (with adjustment), the researchers did compare the treatments and found a significant (real) but modest (about 6 calories) superiority for the treatment that listed the number of miles it would take to walk off a bottle of soda or juice compared to the average across all treatment conditions.  For example, in the analysis of all the beverage sales,  the average calories sold for any information treatment was 184 (compared to 203 without information), but the average calories sold in the walking 5 miles treatment was 179.

During the last week of information disclosure, the researchers conducted exit surveys with a small group of randomly selected beverage customers (who were black adolescents). The surveys explored whether or not the youth saw, understood, believed and considered the information.  Please see the full article to read about the findings.1

Lastly, and importantly, the researchers continued to track sales for 6 weeks after removing all of the nutrition signs.  They did this to test lasting effects and indeed all of the outcomes, though attenuated, remained in effect.

I am a researcher in this same area – though my focus is on nutrition labeling law. I understand that calorie only disclosures are not always effective or as effective as public health advocates would like them to be and I find the literature on multiple traffic light labeling more promising.  Others find the literature on exercise equivalents, to which the Bleich et al study belongs, to be equally or more promising.  So, I think that is what the press is capitalizing on – exercise equivalents did change behavior in this study, but the press isn’t doing a good job of telling the rest of the story.  In this sample of black youth, who as a population have a disproportionate prevalence of obesity and soda consumption, just providing a calorie disclosure at the point of sale led to positive changes in all outcomes.  That is GREAT news!   As the federal law now stands, the only disclosure mandated is calories and Bleich et al give us hope that even if we can’t modify the law's directive, nutrition labeling could still positively impact a high risk group.

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