Reviews of Sweeteners’ Impact on Body Weight Focus on Different Studies and Produce Different Findings

Washington D.C. — There is consensus among nutritionists that individuals should limit added sugar intake, owing to the association between added sugars intake and risk of obesity, type 2 diabetes mellitus, cardiovascular disease, and dental caries. However, there is no consensus as to what added sugars should be replaced with, if replaced at all.

A new paper conducted an overview of reviews to systematically evaluate the methods and findings from published reviews that attempted to answer the question “what is the estimated effect of low-calorie sweetener consumption on body weight?” This research was conducted to better understand why reviews designed to ask the same question sometimes arrive at different conclusions.

The paper was supported by the Institute for the Advancement of Food and Nutrition Sciences and was carried out by nutrition and public health researchers. It is currently available online in the peer-reviewed journal Advances in Nutrition.

As part of this research, published studies called “systematic reviews” and “meta-analyses” were identified. A systematic review is a secondary research method that collects and synthesizes results from studies related to a specific topic to answer a research question. A meta-analysis is a statistical analysis method that combines results of multiple, similar studies to generate an overall estimated effect.

The authors of this overview of reviews found that systematic reviews designed to determine the association between low-calorie sweetener (LCS) consumption and body weight use different inclusion criteria, literature search methods, and strategies for evidence synthesis, pooling data from different studies.

Despite these differences in methodology, there was a consistent pattern that meta-analyses of randomized controlled trials suggest that LCS are beneficial for body weight management (particularly when compared with sugars) or have no effect on weight. Conversely, meta-analyses of non-randomized studies (i.e., observational research of study participants not randomly assigned to study groups) tend to report adverse associations.

Fundamentally, differences between randomized controlled trials (RCT) and non-randomized studies contribute to differences in results which are amplified when combined as part of a systematic review. RCTs are considered the highest-quality evidence owing to the randomization of the intervention, which reduces the risk of confounding or muddying the findings with other influences. However, RCTs are often limited by their short duration and ability to be applied to broader populations.

The limitations of individual studies, particularly among non-randomized studies, become inflated when combined in meta-analyses, producing “very precise but equally spurious results,” according to the study authors. The authors argue this can lead to a false sense of precision which should be interpreted with caution. The statistical combination of results of highly heterogenous studies should not be conducted in the first place, they found.

In conclusion, systematic reviews investigating the effect of LCS on body weight use different methods to answer similar, but different, research questions. This may explain why some reviews conclude that LCS consumption may help manage body weight when substituted for sugars, and some have not — complicating nutrition counseling.

According to lead author and Managing Scientist Kelly Higgins, Ph.D., with the Exponent, an engineering and scientific consulting firm, “Consumers are interested in a black or white recommendation regarding whether they should avoid or consume certain foods or beverages. Attempts to answer this question with systematic reviews can make this relationship seem more blurred. We hope this research highlights the importance of using high-quality primary research when developing dietary recommendations related to low-calorie sweeteners.”

The paper is available here.

The Institute for the Advancement of Food and Nutrition Sciences (IAFNS) is committed to leading positive change across the food and beverage ecosystem. This paper was supported in part by IAFNS Low- and No-Calorie Sweetener’s Committee. IAFNS is a 501(c)(3) science-focused nonprofit uniquely positioned to mobilize government, industry and academia to drive, fund and lead actionable research. iafns.org