Sugar is Bad but Artificial Sweeteners are WORSE
Animal studies suggest that artificial sweeteners may be addictive. A 2007 paper reports that, in studies of rats exposed to cocaine and then given a choice between intravenous cocaine or oral saccharine, most chose saccharin.
A 2008 paper in Obesity showed that those who used artificial sweeteners gained more weight over a seven- to eight-year period than those who did not.
A large study published in the American Journal of Clinical Nutrition in 2013 which involved almost 70,000 women over 14 years found that subjects consuming sugar sweetened beverages were at an increased risk for becoming type 2 diabetics. Their risk was increased by around 34%. This was as expected and similar increases had been seen mostly in US populations for a while. What was interesting and perhaps unexpected was the finding that those women who chose to drink sugar-free, artificially-sweetened beverages experienced double an increase in risk for diabetes compared to the sugar group!
A 2014 study then showed that that the reason people become less glucose tolerant when drinking artificially sweetened beverages is because consumption of artificial sweeteners causes profound changes in the gut bacteria (microbiota).
Certainly, drinking sugar-free beverages is good advice. You just need to NOT to add artificial sweeteners to them!
REFERENCES
2007:
Intense sweetness surpasses cocaine reward
http://www.ncbi.nlm.nih.gov/pubmed/17668074
2008:
Fueling the Obesity Epidemic? Artificially Sweetened Beverage Use and Long-term Weight Gain
http://onlinelibrary.wiley.com/doi/10.1038/oby.2008.284/abstract;jsessionid=4FD5565601D88142CEFE6EE9822DA2C5.f04t02
2013:
Consumption of artificially and sugar-sweetened beverages and incident type 2 diabetes in the Etude Epidémiologique auprès des femmes de la Mutuelle Générale de l’Education Nationale–European Prospective Investigation into Cancer and Nutrition cohort
http://ajcn.nutrition.org/content/97/3/517.long
2014:
Artificial sweeteners induce glucose intolerance by altering the gut microbiota
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13793.html