Artificially sweetened diet drinks make no difference to weight gain and should not be seen as healthier than their sugar-laden counterparts, according to a team of experts.
A review of research evidence concluded there is nothing to support claims that sugar-free versions of popular soft drinks can help combat obesity and related diseases such as Type 2 diabetes.
Industry-sponsored studies reporting "favourable" associations between diet drinks and weight loss may be biased, it claimed.
There have been concerns that diet drinks, known as artificially sweetened beverages (ASBs), might lead people to consume more calories by stimulating sweet flavour taste buds.
The new study found that evidence relating to the healthiness of ASBs was inconclusive with randomised controlled trials (RCTs) producing mixed results.
Senior investigator Professor Christopher Millett, from Imperial College London's School of Public Health, said: "A common perception, which may be influenced by industry marketing, is that because 'diet' drinks have no sugar, they must be healthier and aid weight loss when used as a substitute for full sugar versions. However, we found no solid evidence to support this."
Manufacturing diet drinks was also said to have "negative consequences" for the environment. Up to 300 litres of water was required to produce a single half-litre plastic fizzy soft drink bottle.
The investigators pointed out that research supported by food or beverage companies was more likely to find no evidence of links between sugary drink consumption and obesity than non-industry sponsored research.
Similarly, ASB industry-sponsored research was "more likely to report favourable results and conclusions regarding ASB effects on weight control".
In many cases, researchers had failed to disclose conflicts of interest relating to links with the food industry, it was claimed.