3 Things You Need to Know about the Latest Sugar-Sweetened Beverage Claims

The latest headlines could definitely make us panic about having the occasional soda. Because we recently dove into both junk science sins and how studies can get distorted in press releases, we knew we had to dig into the original research.

correlation-causation-nutshell

The consumption of sugar-sweetened beverages (SSBs) is being scrutinized the world over, both literally and figuratively. Health effects attributed to them now apparently include death. Wait ... did I hear that right, death? A new study claims that 184,000 global deaths annually are the direct result of consuming SSBs. While nobody would debate the role in obesity and other negative health consequences that can result from lack of exercise and over-consuming calories (SSBs included), can the drinks themselves really endanger lives? Let's take a closer look at how this latest study came to such conclusions. Here are three big questions we ask from our Guide for Evaluating Scientific Evidence. Hopefully, they’ll help you put the study in context too.

 

1. Were the study methods sound?

This study collected data on self-reported SSB consumption. The researchers pooled data from national dietary surveys from across the globe. The study derived the associations of SSB intake on body mass index (BMI) and diabetes, as well as deriving the effects of elevated BMI (but did not assess the impact of excess calories in the diet) on cardiovascular disease, diabetes, and cancers, from large prospective cohort pooling studies. The study then integrated self-reported SSB consumption levels into complex modeling formulas to yield morbidity (media condition) data. Think, "if A leads to B -- which is an unproven assumption in the first place -- and B leads to C, then maybe A leads to C?" It’s a classic example of correlation (see at right). 

Dietary recall data relies on subjects to divulge their exact eating and drinking patterns and is a widely used method to capture food and beverage intake information. But how accurate is dietary recall? There are concerns. Dhurandhar and colleagues have published on the reliability of self-report data and argue for the use of objective measures—not dietary recall—to guide clinically relevant healthcare policies and research.

Prospective cohort studies (observational data) are also a commonly deployed research method. While they cannot be used to claim causal links, cohort studies can generate associations and hypotheses for future study. They do this by following a group of people who share common characteristics and assess whether exposure to a certain risk factor leads to a certain outcome. The highest forms of scientific evidence are from Systematic Reviews and Meta-Analyses of Randomized Controlled Trials (RCT), individual RCT, and non-Randomized Controlled Trials. 

hierarchy-of-evidence-cohort-studies

2. Do these findings fit with similar studies?

When examining a research study, it’s always important to consider how the findings compare to existing literature on the topic. According to the authors, “this investigation represents the first comprehensive, systematic assessment of the worldwide burdens of diabetes, CVD, and cancers attributable to SSBs,” so it’s difficult to compare these findings with others.

There is available cohort and RCT data on the relationship between SSB consumption and health effects such as body weight and heart disease. Generally speaking, when (high versus low) SSB consumption data is compared in cohort studies, you do see increases of diabetes, gout, hypertension, CHD, stroke, and obesity with high consumption. In fact, these existing estimates were the very numbers the authors used in this study. However, consumers of SSBs also tend to smoke more, exercise less, and have a poorer overall diet quality. It's worth noting that none of these other important health factors were controlled for in this study's analysis.

When other researchers have examined SSB effects using energy-adjusted models and isocaloric exchanges with other forms of carbohydrates, no association between SSBs and body weight or adiposity (body fat) has been shown. (Te Morenga et al., 2013Malik et al., 2013; Kaiser et al., 2013; Sievenpiper et al., 2012) Additionally, there are other dietary factors that may influence weight as much or more than SSBs. (Mozaffarian et al. 2011)

While many studies of varying design have been conducted on the role of SSBs and added sugars consumption on weight, fewer have studied the potential impact on heart disease. Importantly, no RCTs have assessed the direct impact of added sugars on heart disease. They have instead primarily focused on risk factors for heart disease. Results have generally been mixed with the highest levels of consumption observing the most positive associations, again relying on self-reporting to determine consumption. Research in this important area of study continues.

Speaking of dietary quality, the data set that was used in the present study on disease-specific mortality/morbidity was from Global Burden of Diseases, Injuries, and Risk Factors 2010 Study. This data set was also assessed by Lim et al. Lim and colleagues found that the highest dietary risk factor for morbidity was with diets low in fruits and vegetables, not with those containing SSBs. The fact that consuming few fruits and vegetables was significantly more associated with morbidity than SSB consumption (4.7 million versus 184,000 -- a pretty big difference!) was also acknowledged by the authors, but it didn't make media headlines. It’s always important to keep the true risks in perspective. With the graph below, for example, you can see some of the risk factors that really contribute to morbidity and mortality.

morbidity-mortality-risk-factors-chart

3. Should the study impact my diet?

There’s a lot to consider, from the correlation/observation study design, to reliability of dietary recall data, to the context of previous work on dietary risks. What does that mean for how this data impacts our decision-making? To help put these considerations into perspective, we turned to three respected experts for their insights:

Dr. Roger Clemens is an Adjunct Professor at the University of Southern California (USC) focused on nutrition and food safety. Dr. Clemens referenced his work on the 2010 Dietary Guidelines Advisory Committee (DGAC), saying, “as stated by the 2010 DGAC, sugar, when consumed in excess, may contribute to increased risk in various conditions, including adiposity.  The key word here is excess.”

Dr. Mark Kern is a professor at San Diego State University focused on the effects of diet and exercise on nutritional status. Dr. Kern noted that “while the data do suggest that links exist [between SSBs and disease risk], they do not indicate cause and effect. [They] fail to indicate at what dose sugar-sweetened beverages should not be exceeded.” His point about quantity is an important one as we balance out diets, as moderation can be critical for successful diets.

Dr. Andrew Brown, a scientist at the University of Alabama at Birmingham, noted that the data included in the models were tenuous at best. “The estimates rely on self-report, which are of poor quality. Dietary misreporting is associated with other disease predictors, including obesity and socioeconomic status,” making true intakes and disease associations difficult to determine. He further pointed to the fact that the new paper used associations between SSBs and BMI from a United States population to extrapolate to the world. “When you create a model with one of the assumptions being that the exposure causes harm,” Brown said, “the results are not going to determine whether the model shows if there is harm, but only how much.” He finds predictive models of this type potentially useful to provide more concrete predictions of the effects of interventions or policies, but finds “the use of such models in the peer-reviewed literature to state ‘urgent’ needs for action to be activism shrouded in science.”

Dr. Kern also emphasized that “the data from this study do indicate a need for more rigorous research on the effects of sugar-sweetened beverages through randomized clinical trials. In particular, there are needs to examine dose responses to sugar-sweetened beverages with special attention to determine doses that might be harmful in both individuals who are and who aren't simultaneously consuming a healthful diet and meeting recommended physical activity guidelines.”

The Bottom Line

So what should you prioritize in your diet? Consuming too many calories from any single calorie source (SSBs included) can lead to weight gain. An actionable step to managing weight is identifying what your major sources of excess calories are and then working to cut back on those items. Keep splurges sensible; focus on getting the nutrients you need from fruits and vegetables, whole grains, dairy, and lean protein; and make sure you’re balancing your intake with physical activity.

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