A critical appraisal of the BMJ paper by Toews et al that claimed no benefits or harms for low calorie sweeteners
Highlights:
- Health benefits of low calorie sweeteners are clear when used to replace sugars in the diet: they help reduce calorie intake, they do not cause a spike in blood glucose, and they do not contribute to tooth decay
- The study by Toews et al did find some benefits for low calorie sweeteners’ use over sugar in both adults and children but called for more research as current evidence is weak
- It should not be expected that low calorie sweeteners, by themselves, would act as magic bullets in weight loss, but they can be useful when used to replace sugar calories
A recent review published by Toews and colleagues in the British Medical Journal (BMJ) in early January 2019 gained widespread media attention and led to headlines in mainstream media such as “sweeteners have no health benefits over sugar”, “no benefits, no harms for sugar substitutes”, “sweeteners: not good, not bad”. But do these headlines reflect the actual outcome of the systematic review by Toews and colleagues or what the collective evidence (some of which has not been considered in this new review) shows? The answer is simply no.
What did the study find?
So, first of all, let’s have a careful look at what the systematic review and meta-analyses by Toews et al actually found, based on the analysis of 56 studies including 17 randomised controlled trials (RCTs), which provide higher quality of evidence.
- In adults, mean daily energy intake was about 250 calories lower in people consuming low calorie sweeteners than in those receiving sugar, based on the study’s meta-analysis of four RCTs. Similarly, sugar intake was also found to be lower in consumers of low calorie sweeteners. Also, current studies show no effect on feelings of hunger or on appetite.
- Evidence indicated a small beneficial effect of low calorie sweeteners on body mass index (BMI) and fasting blood glucose, but this is based on a limited number of clinical studies included in the review (5 RCTs). However, due to the inclusion criteria set by the authors, important, large and well-designed RCTs of longer duration were excluded from their analysis. So, for example, the recent 1-year trial by Peters et al. (2014, 2016) that studied the impact of daily consumption of low calorie sweetened drinks on body weight in 303 participants, and which showed a clear benefit of diet drinks in weight loss and maintenance, has not been considered in the Toews et al analysis.
- When the meta-analysis estimated effects of low calorie sweeteners on overweight and obese people specifically, their use resulted in reduced body weight of approximately 2kg (3 RCTs), which could be an important benefit for individuals who need to pay more attention and manage their weight.
- Among children, the intake of low calorie sweeteners led to a smaller increase in body mass index z score than sugar intake, but no difference was found on body weight.
- No other statistically or clinically relevant health effect of low calorie sweeteners’ intake has been found, including no increased risk for cancer. The safety of low calorie sweeteners has been repeatedly confirmed by regulatory authorities around the world.
So, the review by Toews et al did find some benefits for low calorie sweeteners in relation to calorie and sugar reduction, modest weight loss and fasting glucose reduction. Not unexpectedly, these benefits have been found when low calorie sweeteners are compared to sugar. Low calorie sweeteners, by themselves, have no weight- or glucose-lowering properties, so their benefits are evident when used to replace sugars and thus calories in the diet.
The authors of the review also point out that the level of evidence is of very low to moderate quality and more longer-term studies are required, and thus they conclude that: “There was no compelling evidence to indicate important health benefits of non-sugar sweetener use on a range of health outcomes.” This conclusion is in contrast with earlier comprehensive systematic reviews and meta-analysis on low/no calorie sweeteners and body weight, supporting that, overall, the balance of evidence indicates that use of low/no calorie sweeteners in place of sugar, in children and adults, leads to reduced energy intake and body weight (Rogers et al, 2016). Much of the inconsistency among these publications stems from decisions made by Toews et al. in selecting or excluding relevant papers in the meta-analyses. Only a limited number of studies have been considered for each outcome, excluding several high-quality randomised controlled trials (RCTs) and long-term cohort studies with repeated measurements.
Several scientific experts provided comments on this study, emphasising that Toews et al. excluded several relevant RCTs in adults, and even inappropriately included one RCT which had a large effect on the overall result (Rogers, 2019). Experts noted that Toews et al. covered a unique and particularly small sub-set of existing publications (Bellisle, 2019) and that they omit or disregard many studies showing benefits from sweeteners (Winkler, 2019).
Commenting on the study by Toews et al in an editorial published in the same issue of BMJ, Vasanti Malik states that, “the weight of evidence hints at benefits, but the full picture has yet to emerge” (Malik V, 2019). In the linked editorial, Dr Malik pointed out that: “While meta-analyses are important for guiding recommendations and policies, individual high quality studies should also be emphasised. For example, trials by de Ruyter and colleagues and Ebbeling and colleagues, the largest and most rigorously conducted so far, provide strong evidence that the replacement of sugar sweetened beverages with diet alternatives reduces weight gain in children and adolescents after one year of follow-up.” The author concludes: “Based on existing evidence including long term cohort studies with repeated measurements and high quality trials with caloric comparators, use of NSS as a replacement for free sugars (particularly in sugar sweetened beverages) could be a helpful strategy to reduce cardiometabolic risk among heavy consumers, with the ultimate goal of switching to water or other healthy drinks.”
What the collective evidence shows?
Previously published systematic reviews and meta-analyses that have examined the totality of the published studies investigating the effects of low calorie sweeteners on body weight, and importantly have examined these effects in relation to caloric sweeteners, confirm the beneficial effects of low calorie sweeteners in calorie reduction and in modest weight loss when used to replace sugar (Rogers et al, 2016; Miller and Perez, 2014). In fact, the methodological and clinical inclusion and exclusion criteria used in these previously published systematic reviews differed substantially from the criteria of the latest review, resulting in a largely different and limited pool of included studies in the Toews et al paper. For example, the Rogers et al meta-analysis included 10 trials with 12 comparisons that examine effects on body weight versus 5 trials in the Toews et al paper; the number of included studies is much higher for short- and longer-term effects on energy intake. Also, another notable issue with the selected inclusion criteria of the Toews et al review is that by not placing any restrictions on study design, this strategy allowed the inclusion of cross sectional and non-randomised designs that are prone to confounding and reverse causation, as well as case control studies that are vulnerable to selection and recall bias (Malik V, 2019).
Similarly, the benefit of no effect of low calorie sweeteners on blood glucose (versus sugar that causes a spike in blood glucose after consumption) has been re-confirmed in recent systematic reviews and meta-analyses (Nichol et al, 2018; Tucker and Tan, 2017). The European Food Safety Authority (EFSA) has reached the same conclusion in a scientific opinion published in 2011 supporting that, “Consumption of foods containing intense sweeteners instead of sugar induces a lower blood glucose rise after their consumption compared to sugar-containing foods”. (EFSA, 2011)
Finally, another important benefit of low calorie sweeteners relates to dental health, as low calorie sweeteners are not fermented by oral bacteria and thus do not contribute to tooth decay. This has also been recognised by EFSA in its 2011 opinion, which supported that “the consumption of foods containing low/no-calorie sweeteners instead of sugar contributes to the maintenance of tooth mineralisation”. (EFSA, 2011)
Take-away message
In conclusion, low calorie sweeteners do have benefits when used in place of sugars in the diet. The study by Toews et al does not show any different outcome, but it notices that more research is needed to confirm their effects. On the other hand, what is certainly well established is that excess sugars’ intake should be reduced and that low calorie sweeteners are a useful tool in helping people to meet this dietary goal.
