Food and diet

No proof that sugar-free soft drinks are healthier, argues review

"Soft drinks made with artificial sweeteners, such as diet colas, do not help people lose weight and may be as big a part of the obesity problem as the full-sugar versions," The Guardian reports.

While the headline may sound definitive, this was the conclusion of an opinion piece (or narrative review), not evidence based on new research.

The big food and drink manufactures have responded to increasing concerns about the impact of sugar-sweetened beverages on health, such as increasing rates of tooth decay and type 2 diabetes, by promoting artificially sweetened drinks as a healthy alternative.

However, recent evidence suggests these may not actually be a better option, and this review wanted to look into this further.

The review argues that artificially sweetened drinks are just as bad as sugar sweetened drinks and says that the national dietary guidance shouldn't recommend consumption of artificially sweetened drinks as an alternative.

The review concludes there is an "absence of consistent evidence" that artificially sweetened drinks can improve health outcomes such as helping people achieve a healthy body weight. But absence of evidence is not the same as evidence of absence. Due to the unsystematic nature of the review we can't be sure all relevant evidence was considered.

Where did the story come from?

The review was carried out by researchers from various institutions in the UK, US and Brazil, such as Imperial College London, Washington University in St. Louis and the University of São Paulo. Individual researchers reported various sources of funding, including the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and an NIHR Research Professorship award.

The review was published in the peer-reviewed medical journal PLOS Medicine, an open-access journal, so the study is free to read online.

As expected, the UK media jumped on the claims that "diet drinks" should not be seen as the healthier option. But most sources gave the mistaken impression, at least in the headlines, that this was new research as opposed to a review of existing evidence.

However, most did delve into the limitations of the review further down in their reports.

What kind of research was this?

This was an evidence-informed narrative review which assembled data from various avenues of research. The review explored the hypothesis that artificially-sweetened drinks aren't actually a better option than sugar-sweetened drinks.

The researchers assessed evidence from different types of study such as randomised-controlled trials (RCTs) and observational studies. They also discussed some of the strengths and limitations associated with each study design.

The methods behind how the literature was identified weren't described; there wasn't mention of whether databases were searched or criteria for inclusion and exclusion. As such, it isn't possible to say whether the review was carried out in a systematic manner.

Non-systematic reviews are useful for summarising research on a particular topic, but run the risk of missing counterarguments and other relevant evidence.

What did they find?

The review starts by providing some background on sugar sweetened and artificially sweetened drinks and their suspected links with the global obesity crisis. In turn, the obesity crisis is thought to be responsible for the sharp rise in non-communicable diseases (diseases not caused by infection, such as type 2 diabetes).

It also highlights the ways in which guidelines and policies have been developed to address growing health concerns.

The review goes on to outline evidence about the potential impact of artificially sweetened drinks. It acknowledges that several systematic reviews of observational cohort studies and randomised controlled trials have found an association between artificially sweetened drinks and weight loss.

It also raises the point that there are long-standing concerns that replacing sugar sweetened drinks with artificially sweetened drinks may trigger various mechanisms in the body.

These may include increased appetite, increased preference for sweet taste, or simply overconsumption of solid foods due to awareness of the low calorie content from artificially sweetened drinks. However, these concerns were not backed up by any solid evidence.

The main points revolve around the potential negative health impact of artificially sweetened drinks. It also touches on the environmental impact of sweetened drinks, and goes on to discuss the implications for policy.

The researchers state that although national dietary guidelines generally recommend avoiding or reducing our intake of sugar sweetened drinks, the guidance surrounding consumption of artificially sweetened drinks is mixed. 

What did the researchers conclude?

The researchers conclude: "the absence of evidence to support the role of ASBs [artificially sweetened beverages] in preventing weight gain and the lack of studies on other long-term effects on health strengthen the position that ASBs should not be promoted as part of a healthy diet.

"In practice, this means that ASBs should not be recommended in dietary guidance and be subject to the same restrictions on advertising and promotion as those imposed on SSBs. New taxes implemented on SSBs should be applied at the same level to ASBs."


This review assessed a range of research exploring the the potential negative health impact of artificially sweetened drinks, compared to sugar sweetened drinks. The review is fairly one-sided, discussing the links between artificially sweetened drinks and the global obesity crisis, as well as the negative environmental impact of sweetened drinks.

The researchers suggest that national dietary guidance shouldn't recommend consuming artificially sweetened drinks as an alternative to sugar sweetened drinks.

However, a number of experts commenting on the review expressed the opinion that despite the lack of evidence for the benefits of artificially sweetened drinks, "diet drinks" were a better option than sugar sweetened drinks for people trying to lose weight.

Professor Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow commented, saying:

"I do not agree with the suggestion that diet drinks are no better than sugary drinks in terms of body weight. Whilst I agree the evidence base in terms of proper trials comparing sugary drinks with diet drinks are lacking for real end-points like weight or heart disease, intuitively a drink which contains lots of calories (i.e. sugary drinks) versus one that contains few or no calories (i.e. diet drinks) must be worse for health given clear adverse effects on dental health and clear gain of calories and so weight gain potential. To suggest otherwise would be irresponsible."

Prof Susan Jebb, Professor of Diet and Population Health at Oxford University said "artificially sweetened drinks are a step in the right direction to cut calories".

You could arguably draw a comparison between artificially sweetened drinks and e-cigarettes; neither may be ideal but they are both better than the alternative. 

NHS Attribution