Mixing spirits with diet soft drink makes the alcohol more potent than mixing with sugary soft drinks, according to a US study.
Researchers from Northern Kentucky University found people who drank alcohol with artificially sweetened drinks had higher breath alcohol concentration than those who mixed with a regular sugar-sweetened soft drinks.
In the study, eight men and eight women attended three sessions where they were given different drinks –– a vodka with diet soft drink, a vodka with normal soft drink, and a diet soft drink with no alcohol.
They were breath-tested after each drink and were also asked to assess how drunk they felt and whether they felt okay to drive. They were also given a reaction time test.
The researchers discovered that the vodka-diet drink cocktail led to a significantly higher score on the breath test, and also led to more behavioural impairment.
"We are talking about significant differences here," study author Cecile Marczinski, an assistant professor of psychology at Northern Kentucky University, said in a media release.
"Participants who drank diet soda with vodka had blood alcohol contents as high as 18 percent more than when sugar-containing mixers were used."
The researchers believe that mixing alcohol with sugary-drinks signals the stomach to digest the drink like a meal, which delays the absorption of alcohol into the bloodstream.
Diet soft drinks don't trigger the same stomach reaction so the alcohol can reach the bloodstream quicker.
"Artificially sweetened alcohol mixers do not really elevate alcohol intoxication. Rather, the lack of sugar simply allows the rate of alcohol absorption to occur without hindrance," said Professor Dennis Thombs, from the University of Northern Kentucky, who has also researched the impact of mixers on blood alcohol content.
Marczinski said having a spirit with diet soft drink could put you over the safe driving limit, when a normal soft drink mixer wouldn't.
"The choice of what you mix your alcohol with can make a difference," she said.
"In the long run, it's more harmful for your body to be exposed to a higher alcohol concentration than a few extra calories."
Michael Thorn, chief executive of the Foundation for Alcohol Research and Education, warned that people need to watch their levels of alcohol intake.
"Drinkers would be far better served concerning themselves with reducing their alcohol consumption rather than focussing on the merits of diet vs non diet soda mixers," he told ninemsn.
"Alcohol use and misuse is the cause of substantial harms to the Australian community. Too many Australians continue to drink at unsafe levels, with 80 percent of the alcohol consumed by people aged 14 to 24 is consumed in ways that put the drinkers and others lives at risk."
Previous research found women are more likely to mix diet soft drinks with alcohol.
The research will be published in the April issue of Alcoholism: Clinical & Experimental Research.