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A recent article in The Guardian, "No evidence sugar-free soft drinks aid weight loss – study", challenges the effectiveness of diet drinks and argues:

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, academics have said.

A paper by researchers at Imperial College London and two universities in Brazil contends that artificially sweetened beverages, often called diet drinks, are just as big a problem as those containing sugar. There is no evidence they help people lose weight, they say, possibly because people assume they can eat more because their drinks are low in sugar.

Is the cited paper correctly reported? Is the paper effectively challenging, correcting or disproving previous science?

  • I've trimmed down the body text while keeping pretty much all the questions you had. First, we need to verify that the reporting is correct, if so, whether there is any actual new science. This will also cover the title question. – Sklivvz Jan 5 '17 at 14:26
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The paper cited is available online.

It does not exactly claim that artificially sweetened beverages ("ASBs") "do not help people lose weight". What it actually says is this:

In summary, the available evidence does not directly support a role of ASBs in inducing weight gain or metabolic abnormalities but also does not consistently demonstrate that ASBs are effective for weight loss or preventing metabolic abnormalities. Evidence on the impact of ASBs on child health is even more limited and inconclusive than in adults.

In other words, the available evidence doesn't let us tell whether ASBs are good or bad or neutral. (It is unsusprising that a newspaper article reduces this to "ASBs don't help".)

It does not exactly claim that ASBs "may be as big a part of the obesity problem as the full-sugar versions", but it does say this:

Far from helping to solve the global obesity crisis, characteristics related to ASB composition (low nutrient density and food additives), consumption patterns (potential promotion of sweet taste preference), and environmental impact (misuse of natural resources, pollution, or ecotoxicity) make them a potential risk factor for highly prevalent chronic diseases.

In other words, ASBs may well do harm (but the article doesn't make any particular claim about the size of that harm relative to whatever good they may turn out to do).

It does (see above) claim that "there is no evidence they help people lose weight". And it does say that one possible mechanism for this is that "people assume they can eat more because their drinks are low in sugar", though that isn't the first mechanism the article mentions:

The main proposed mechanisms are that ASBs stimulate sweet taste receptors -- which could theoretically increase appetite, induce preference for sweet taste, and modulate gut hormone secretion -- or result in overconsumption of solid foods due to awareness of the low calorie content of ASBs [33].

So, in answer to the first question ("is the cited paper correctly reported?"):

  • The reporting is about as accurate as newspaper reporting of scientific articles usually is: it isn't altogether wrong but it fails to distinguish between "there is no evidence for X" and "not-X" and misses out lots of details.
    • Specifically, it does say that there is no evidence that ASBs help people lose weight, and the mechanism mentioned in the newspaper article is one of the ones it mentions; but it doesn't say anything so definite as that ASBs don't help people lose weight.
  • Perhaps unusually, the title ("No evidence sugar-free soft drinks aid weight loss") appears to be more accurate than the article itself ("... do not help people lose weight").

The second question asked here is: "Is the paper effectively challenging, correcting or disproving previous science?" The paper is actually reporting previous science, but one could still ask whether the research it describes overturns previously accepted science. I bet the answer is no, and that there has never been a scientific consensus that ASBs are a big win for health or obesity, but this is not the sort of thing it is easy to find good evidence of. The paper itself certainly makes no claim to be overturning ideas previously thought to have been established by scientific research.

  • What the paper doesn't give a good feel for is the degree of different results in other trials or whether those trials were well conducted. Obervational studies, for example, have shown weight gain is the consumers of diet drinks but these studies suffer from major confounding. RCTs are more mixed but are still not conducted well. To me a possble alternative title would have been: we don't have any good studies. – matt_black Mar 12 '17 at 13:45

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