The Deakin University researchers also dismissed the claims of some drinks manufacturers that the additive has an effect on the flavour of a product.
In a study published in the British Journal of Nutrition, the researchers measured the influence caffeine had on the consumption of sugar-sweetened soft drinks, finding that those drink non-caffeinated products consume less.
The study involved 99 participants aged 18—30 who were randomly assigned to one of two groups: one that would drink lemonade containing caffeine, or one that would consume the same drink, albeit without the additive.
Public health issue
To disguise the true purpose of the month-long study, the participants were told the study was to test the flavour of the drink. They were told they could drink as much of the product as they wanted over that period.
The amount they consumed was recorded each day, while their enjoyment of the drinks was assessed at the beginning and the end of the study.
The results showed that the participants in the caffeinated group drank 419ml per day—equating to 785 kilojoules. This was significantly more than those in the non-caffeinated group, who drank 273ml, or 512 kilojoules, per day.
"Our findings clearly show that caffeine as an additive in soft drinks increased consumption and with it sugar calories, and that is a significant public health issue given the prevalence of obesity," said Associate Professor Lynne Riddell of Deakin’s Centre for Physical Activity and Nutrition Research (C-PAN), the study's senior author.
"This research supports the ongoing need for caffeine to be tightly regulated as an additive in the food supply, as it appears [to be] an ingredient for overconsumption.”
No taste difference
Meanwhile, a separate group of trained flavour testers backed up previous C-PAN research when they found no difference in the flavour between the caffeinated and non-caffeinated drinks.
Large soft-drink manufacturers claim that caffeine is added as a flavour enhancer however this claim is challenged by this research, said Professor Russell Keast, who authored the flavour study.
"Participants cannot taste the difference between the caffeinated soft drink and the non-caffeinated soft drink; if you can't tell a difference in flavour there is no flavour activity," said Keast.
The level of caffeine in the soft drinks used in the study was the same as in commercially available cola flavoured beverages.
"The caffeinated soft drinks were also better liked than the non-caffeinated soft drink at the end of the study, supporting previous research that suggest caffeine promotes liking and consumption via sub-conscious influences that may be related to reversing caffeine withdrawal symptoms.”
Echoing Riddell’s sentiments, Keast said his research showed the need for greater regulation of caffeine in foods and drinks.
Industry responds
Currently, more than 60% of soft-drinks on the market contain caffeine, the researchers said.
Geoff Parker, chief executive of the Australian Beverage Council, called the researchers’ demands for more caffeine regulation to reduce obesity “misguided and out of step with reality”.
Noting flaws in the study, which was unable to determine any changes in body mass between the two groups tested, Parker said the low number of participants involved “should be kept in context of the evidence base when considering future policy settings on caffeine in drinks”.
“Sugar contribution from carbonated soft drinks has dropped between 1997 and 2011 by 26% per capita as consumers switch from sugar-sweetened to non-sugar sweetened soft drinks. Today, adults get just 1.8% of their kilojoules from soft drinks and children just 2.2%,” he said.