If your curiosity about low-calorie sweeteners (LCS) is growing, you’re not alone. We get a lot of questions about them: “Will they help me lose weight? Are they safe? Should I avoid them?”, to cite a few. Researchers have sought to answer such questions through decades of scientific research. For those that follow the field, it seems as though a new study is published every week.
Well, it’s a new week, so that must mean it’s time for a new study! This latest one, Azad et al., published in Canadian Medical Association Journal examined the scientific literature for evidence on whether routine consumption of LCS is associated with adverse long-term cardiometabolic effects, with the primary focus on body mass index (BMI).
Since this study is receiving quite a bit of attention, here are a few things to consider (from the actual paper) when evaluating evidence from scientific research.
What type of study is this?
To answer this question, we need to first talk about study design. This paper is a new study of existing research where authors conducted what’s called a systematic review and meta-analysis. In other words, this study examined multiple individual research studies and synthesized some of them in a qualitative fashion (via systematic review) and others through a more quantitative mechanism (via meta-analysis). The purpose of setting up these reviews was to assess where the scientific consensus nets out on the impact of LCS on BMI. To do this, their inclusion criteria accepted data from seven randomized controlled trials (RCTs) and 30 prospective cohort studies. The RCTs were published between 1997 and 2016, with interventions ranging from six to 24 months, and prospective cohort studies published between 1997 and 2015, with follow-up ranging between one and 38 years.
What were the results of this study?
Interestingly, the study found conflicting results in the data generated from the two study designs. Data from the RCTs showed LCS consumption had no significant effect on BMI, while data from the cohort studies were associated with a modest increase in BMI. In addition, the authors examined several secondary outcomes. In the cohort studies, associations with increased weight, obesity risk and other cardiometabolic endpoints were observed, whereas data from the RCTs did not establish these relationships.
Can this study establish cause and effect?
RCTs have historically been viewed as the gold standard of evidence, specifically for the ability to test cause and effect. By comparison, observational data, while useful for generating hypotheses, are limited to identifying associations, links or relationships for further testing in controlled trials. Study design is a critical component to scientific research and we’ve written about the the importance of, and limitations to, observational studies before.
Allison Sylvetsky Meni, PhD, an assistant professor in the department of exercise and nutrition sciences at George Washington University’s Milken Institute School of Public Health (who was not involved with the study), pointed out that “this systematic review further highlights the discrepancy between findings of observational studies compared to randomized controlled trials”. According to the study authors, “It is not uncommon for hypotheses based on observational evidence to fail when tested in RCTs, and these data should therefore be interpreted with caution.”
However, additional interpretation of the review’s findings were not just limited to the differences in study design. The study also drew attention to the potential impact of funding source in the RCTs hypothesizing, “Weight loss effects also tended to be stronger in RCTs with industry sponsorship compared with RCTs that were not funded by industry.” While funding source is one factor to consider in research evaluation, it’s certainly not the only, or most important factor.
How does this study compare with recommendations from the 2015-2020 US Dietary Guidelines?
In the US, formal dietary policy is set by the Dietary Guidelines for Americans (DGA). The scientific basis for the DGA comes from the Scientific Report of the Dietary Guidelines Advisory Committee (DGAC). The 2015 DGAC answered its questions about LCS (mainly comparing them to sugar-containing foods and beverages) by using existing systematic reviews and meta-analyses available at the time. The 2015 DGAC assessed the relationship between LCS and measures of body weight and obesity and found consistent evidence that when replacing sugar-containing sweeteners, LCS usage reduced calorie intake, body weight and adiposity. Like Azad et al., the 2015 DGAC also deemed evidence from RCTs to be scientifically stronger than available prospective cohort studies. However, the 2015 DGAC reviewed the highest quality of evidence available, including industry funded research, and did not cite funding sources as a concern.
Others have come to similar conclusions via published RCTs and comprehensive reviews examining various LCS and health issues. If you’re interested in brushing up on scientific consensus around LCS, here are some of those RCTs, meta-analyses and systematic reviews that do not align with the findings in Azad et al.:
- RCTs from Peters et al., 2014 and de Ruyter, et al., 2012
- Meta-analyses and a systematic reviews from Miller 2014 and Rogers et al., 2016
What are the implications of this study’s findings for my diet?
While the 2015 DGAC noted that replacing added sugars with LCS may reduce calorie intake in the short-term, they did have questions about the effectiveness of LCS as a long-term weight management strategy. And this is an important point, because LCS do not cause weight gain, but they do not automatically equate to weight loss either. Decades of research have confirmed these facts, along with a proven track record for safety. LCS are some of the most studied ingredients in our food supply, and research into their potential risks and benefits is ongoing.
In the meantime, regardless of the media headlines you read, LCS shouldn’t be viewed as a magic bullet nor as a detriment to health. They are neither. Instead, they should be viewed as one of many safe options that can be included in your broader weight reduction or maintenance strategies. What’s most important is to build a healthy eating pattern and support it with other health-promoting habits that you can stick to over the long-term. If incorporating LCS into your diet can help you do that, then this new review shouldn’t change your approach.
This post includes contributions from Megan Meyer.