Sweeteners Do Help Reduce Weight
Given global concern about continuing increases in prevalence of overweight and obesity, it is important that evidence about tools to reduce excessive weight is assessed appropriately.
Toews et al.  review the health effects of non-sugar sweeteners (NSS), including effects on energy intake and body weight, the primary targets for NSS use. They conclude that "Most health outcomes did not seem to have differences between the NSS exposed and unexposed groups." A linked news item is titled "Non-sugar sweeteners: lack of evidence that they help to control weight." 
These statements, however, are at odds with our recent meta-analysis.  We concluded that "Overall, the balance of evidence indicates that use of low-energy sweeteners (i.e., NSS) in place of sugar, in children and adults, leads to reduced energy intake and body weight". Such stark differences in conclusions require an explanation.
We have written a detailed analysis of the differences, now being considered for publication. There are two main reasons for the contrasting results.
First, Toews et al. excluded several relevant RCTs in adults. Reasons included that the type of NNS was not sufficiently specified or because the original publication did not provide some data -- information that we easily imputed or obtained from authors.
Second, the inappropriate inclusion of one RCT  had a large effect on the overall result. It compared NSS in capsules with a cellulose placebo, also in capsules. Therefore, the NSS did not replace sugar in any beverages or foods consumed by trial participants -- so a null effect on body weight is to be expected.
NNS are not a magic bullet, because overweight and obesity are not caused solely by excess sugar consumption. Nonetheless, our review shows that NSS do reduce body weight when they substitute for sugar in the diet. Their use is therefore consistent with policies to reduce sugar consumption and excessive weight.
 Toews I, Lohner S, Kullenberg de Gaudry D, et al. Association between intake of non-sugar sweeteners and health outcomes: systematic review and meta-analyses of randomised and non-randomised controlled trials and observational studies. BMJ 2018;363:k4718
 Kmietowicz Z. Non-sugar sweeteners: Lack of evidence that they help to control weight. BMJ 2019, 364:17
 Rogers P, Hogenkamp P, de Graaf C, et al. Does low-energy sweetener consumption affect energy intake and body weight? A systematic review, including meta‐analyses, of the evidence from human and animal studies. Int J Obes 2016;40:381‐94
Maki K, Curry L, Carakostas M, et al. The hemodynamic effects of rebaudioside A in healthy adults with normal and low-normal blood pressure. Food Chem Toxicol 2008;46(Suppl 7):S40-6
Competing interests: Peter Rogers has received funding for research from Sugar Nutrition UK and provided consultancy services for Coca-Cola Great Britain. He has received speaker's fees from the International Sweeteners Association, the Global Stevia Research Institute, the International Life Sciences Institute-India, and PepsiCo R&D, and financial support for travel expenses for other meetings and conferences where he presented research on low-calorie sweeteners.