Scientists have challenged soft drink manufacturers' claims that caffeine improves taste, calling for the use of the addictive substance to be more tightly regulated.
Researchers at Deakin University found the addition of caffeine to soft drinks increases the amount people consume but did not change its flavour.
The study, published in the British Journal of Nutrition, said large soft drink manufacturers claim it is added as a flavour enhancer.
Their study included 99 participants who were split into two groups and given a caffeinated or non-caffeinated version of the same soft drink.
The participants were given one month to drink as much of it as they wanted, with the amount monitored daily.
The results revealed participants given the caffeinated drink consumed 419ml of the soft drink per day, while those who had the non-caffeinated drink consumed only 273ml on average.
Associate Professor Lynn Riddell, from Deakin University's Centre for Physical Activity and Nutrition Research, said the results clearly linked caffeine with consumption.
"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," Professor Riddell said.
"It supports the ongoing need for caffeine to be tightly regulated as an additive in the food supply, as it appears an ingredient for overconsumption."
It is estimated that more than 60 per cent of soft drinks currently on the market contain caffeine.
The study's lead author, Professor Russell Keast, said the results support the findings of existing research showing caffeine having a purely subconscious effect.
"Caffeine promotes liking and consumption via subconscious influences that may be related to reversing caffeine withdrawal symptoms," Professor Keast said.
"Additive compounds such as caffeine that promote consumption via subconscious effects work against efforts to minimise energy consumption.
"The research provides evidence in support of the need for strong regulation of caffeine as an additive to foods."
The research was funded by the Diabetes Australia Research Trust.