Why Do Reviews on Low Calorie Sweeteners and Body Weight Come to Different Conclusions?

Low calorie sweeteners (also referred to as artificial sweeteners, non-sugar sweeteners, or non-nutritive sweeteners) have been used as sugar substitutes for decades and are generally considered safe food additives by the U.S. Food and Drug Administration. While they provide sweetness without calories, their use for body weight management remains controversial. 

Results from studies that assess the association between low calorie sweeteners and body weight vary greatly, resulting in sometimes contradictory dietary guidance. For instance, recent dietary guidance from the World Health Organization (WHO) recommends reduced intake of added sugars while avoiding low calorie sweeteners, based on results from meta-analyses of non-randomized studies showing adverse associations between low calorie sweeteners and body weight in lieu of results from randomized controlled trials, the highest quality research study. However, according to Exponent's Kelly Higgins and co-authors in "An Overview of Reviews on the Association of Low Calorie Sweetener Consumption With Body Weight and Adiposity," non-randomized studies are biased toward concluding that low calorie sweeteners have adverse effects on body weight, whereas randomized controlled studies are more likely to conclude low calorie sweeteners have beneficial or no effect.

In their study supported by the U.S. Department of Agriculture and the Institute for the Advancement of Food and Nutrition Sciences (IAFNS), Higgins and her coauthors analyzed results from systematic reviews measuring the impact of low calorie sweeteners on body weight by determining how the methodologies, inclusion criteria, and data used in the reviews influence findings. They also examined whether meta-analysis — a statistical analysis method that combines results of multiple, similar studies — can generate a consistent, overall estimated effect of low calorie sweeteners on body weight.

The authors found that systematic reviews often used different literature search methods, inclusion criteria, and methods of evidence synthesis to compile highly heterogeneous studies that answered different questions and as a result failed to produce a meaningful estimate of the effect of low calorie sweeteners on body weight. The authors concluded that "[i]nstead of trying to statistically combine studies to explain the complex relationship between [low calorie sweetener] LCS intake and [body weight] BW, using potentially inappropriate statistical methods for this question that continually yield mixed results, it is more appropriate to rely on the high-quality randomized controlled trials [RCT] designed to test specific hypotheses and mechanisms to explain under which conditions LCS intake decreases, increases, or has no effect on BW and develop dietary recommendations for LCS."

From the publication: "Previously published systematic reviews and meta-analyses that attempt to answer the question 'what is the estimated effect of low calorie sweetener consumption on body weight?' report disparate results and conclusions because these reviews attempt to synthesize findings from studies that were designed to test specific but different research questions."