Premature conclusions from isolated studies may lead to biased hypotheses in nutrition science
When it comes to nutrition science, isolated study findings cannot be generalised and interpreted as final evidence. This is perhaps the most important take-away message from a new study by Park et al. published in Cell Metabolism.1 The new study found that sucralose doesn’t increase appetite or food intake in fruit flies, which challenges assertions made by Wang et al.2 last July, based on a study of similar, but not identical, design.
The older Wang et al. study caused big media headlines, basically touting that the results showed that sucralose caused increased food intake in fruit flies – which, therefore, might be a concern for people trying to lose weight. The authors of the new study, Park et al., found that the older research could be explained simply by the fruit flies just getting less food to eat than the controls. In other words, the more likely explanation is that the flies only ate more as a consequence of a caloric deficit (fasting), irrespective of sucralose ingestion.
A big difference between the two studies, was more work done by Park et al., to further investigate what happens when you give fruit flies food with a high concentration of sucralose. The new study points out that conclusions drawn from individual research studies may not always represent the big picture.
‘Sucralose suppresses food intake‘ – reports the new study by Park et al.
In contrast to the study by Wang et al., the new study found that sucralose suppresses food intake under the conditions of the study. Park et al., demonstrated that the resulting food intake during the sucralose exposure period in either study was less than what it was for control flies during this time. The authors reported that this level of underfeeding would explain why the sucralose-treated flies subsequently appeared hungry and later ate more vs. the control flies, for a limited time, when they were re-introduced to control feed.
In considering the importance of low calorie sweeteners in global health, the authors also comment that it’s “vital to avoid premature conclusions on the[ir] potential benefits or risks”. They follow this by noting that their results also do not support a hypothesis proposed by Wang et al., that sucralose might be able to directly trigger a neural state simulating fasting. Instead, Park et al., found that the fasting-like behaviours observed in the fruit flies following intake of sucralose-containing feed was found “likely arising as an indirect consequence of underfeeding.” Overall, Park et al. suggest that the post-sucralose-exposure overfeeding reported by Wang et al. is simply the “consequence of caloric deficit irrespective of sucralose ingestion.” The authors further remark that “our results strongly support the idea that post-exposure hyperphagia is due to compensation for the caloric deficit accumulated during sucralose exposure rather than sucralose ingestion per se.”
A separate commentary by the International Sweeteners Association (ISA) on the Wang et al. study is also available here.
Low calorie sweeteners’ effect on appetite and food intake: What does the collective body of evidence show?
An overwhelming body of evidence supports that low calorie sweeteners do not affect appetite nor cause increased food intake or weight gain in humans. This has been confirmed in recently published meta-analyses and reviews of the scientific literature.
In a recent publication3, Bryant and Mclaughlin (2016) reviewed the outcomes from research on low calorie sweeteners with regard to their ability to affect the gut signals that can affect appetite and food intake. The authors concluded that, while certain animal and/or cellular studies have indicated a potential for low calorie sweeteners to have an effect on this signaling system, there is a lack of evidence that low calorie sweeteners affect human gut function, including gut hormones responsible for appetite control. The conclusions of this paper has been captured in an infographic that can be accessed by clicking here.
In another review published last year4, Peters and Beck reviewed the data from human studies and concluded that randomised clinical trials (RCTs) show that low calorie sweeteners may be helpful in weight management, when used in place of sugar. Similarly, a thorough systematic review and meta-analysis by Rogers et al.5 concluded that there is a considerable weight of evidence in favour of consumption of low calorie sweeteners in place of sugar as helpful in reducing relative energy intake and body weight, and no evidence from the many acute and sustained intervention studies in humans that low calorie sweeteners increase energy intake.
Evidence-based nutrition science embraces the totality of research
While isolated study findings are important to consider, as indicated by Park et al. in their publication, they must not be generalised or reported as final evidence for claims about low calorie sweeteners. Overall, in nutrition science, including research on low calorie sweeteners, it is critical to both avoid premature conclusions that might result from a single research study and look at the entire body of evidence. A wealth of well-designed research supports that approved low calorie sweeteners can help safely lower sugar intake, which can be a useful tool in nutritional strategies for maintaining or lowering body weight.