Study links artificial sweeteners to risk of weight gain, ISA refutes validity

18 Jul 2017 --- A newly published study has found that artificial sweeteners, such as aspartame, sucralose and stevia, may be associated with long-term weight gain and increased risk of obesity, diabetes, high blood pressure and heart disease. In response to the study, the International Sweeteners Association (ISA) has stated that the findings are not supported by the collective evidence from human intervention studies and previous systematic reviews and meta-analysis.

Emerging data indicate that artificial, or nonnutritive, sweeteners may have negative effects on metabolism, gut bacteria and appetite, although the evidence is conflicting.

Researchers from the University of Manitoba's George & Fay Yee Centre for Healthcare Innovation conducted a systematic review of 37 studies that followed over 400,000 people for an average of 10 years. Only seven of these studies were randomized controlled trials (RCT) – the gold standard in clinical research – involving 1003 people followed for six months on average.

According to the researchers, the trials did not show a consistent effect of artificial sweeteners on weight loss, and the longer observational studies showed a link between consumption of artificial sweeteners and relatively higher risks of weight gain and obesity, high blood pressure, diabetes, heart disease and other health issues.

“Despite the fact that millions of individuals routinely consume artificial sweeteners, relatively few patients have been included in clinical trials of these products,” says author Dr. Ryan Zarychanski, Assistant Professor, Rady Faculty of Health Sciences, University of Manitoba. “We found that data from clinical trials do not clearly support the intended benefits of artificial sweeteners for weight management.”

“Caution is warranted until the long-term health effects of artificial sweeteners are fully characterized,” says lead author Dr. Meghan Azad, Assistant Professor, Rady Faculty of Health Sciences, University of Manitoba. 

In a statement, ISA contends that the conclusions of Azad's review are “not supported by the collective evidence from well-designed human intervention studies and previous thorough systematic reviews and meta-analysis.”

Importantly, these claims are not confirmed by the findings of the meta-analysis of randomized controlled trials (RCTs) conducted by the authors of this paper, ISA says.

"Indeed, a strong body of human trials have consistently shown that low-calorie sweeteners can be helpful in weight control, when used in place of sugar and as part of a healthy diet and lifestyle. Contrary to assertions in the study by Azad et al., observational cohort studies, by design, do not and cannot provide evidence that low-calorie sweeteners are linked to weight gain or heart disease, as they are subject to indication bias and reverse causation cannot be ruled out." 

Moreover, ISA states that there is "not a single published randomized controlled trial – the gold standard in nutrition research – that has shown that low-calorie sweeteners’ use can lead to weight gain or any negative health effect."

To put the findings of the study by Azad et al. into context, ISA makes a contention: Some observational studies do find that people who are overweight or obese, and individuals with diabetes or other cardiometabolic health issues that usually accompany obesity, are tending to use low-calorie sweeteners more frequently. However, this might be occurring as a strategy to reduce their calorie and sugar intake, which is a common dietary recommendation in such health conditions. 

Furthermore, in most observational studies, adjustment for variables related to adiposity attenuates or diminishes the observed relations, leading to no significant associations, ISA adds.

In order to attribute the observation of higher obesity rates in frequent low-calorie sweeteners’ consumers to the use of low-calorie sweeteners per se, rather than to some other unmeasured confounding factors, meaning to prove causation, a trial of randomized controlled design is required. This is the only study design in human studies that does rise to the level of demonstrating cause and effect, and in the case of low-calorie sweeteners’ effect on body weight, evidence from RCTs is clear and consistent, pointing to low-calorie sweeteners’ use having a modest benefit on weight loss and maintenance. 

Importantly, trials of longer duration have shown higher weight loss and maintenance with low-calorie sweeteners’ use, ISA adds.