Fizzy drinks have almost halved in price in the last 26 years... fuelling the rise in obesity, according to new research
A study of 82 countries found people can buy 71 percent more cans with their cash than they could in 1990 - making it cheaper than bottled water.
Scientists say the finding underlines the need for taxing the beverages - a move that is being introduced in the UK next year.
It follows UK research last year that showed supermarket cola is now priced so cheaply a serving containing the recommended daily sugar intake for a ten year-old could be bought for just 5p.
Health economist Dr Jeffrey Drope, of the American Cancer Society, Atlanta, said: "Overall in the countries we studied, a person in 2016 could buy 71 percent more sugar sweetened beverages with the same share of their income than they could in 1990.
"Sugary drinks became even more affordable in developing countries, where 2016's income could buy 89 percent more sugar sweetened beverages than in 1990. That's essentially half price."
The study published in Preventing Chronic Disease says fizzy drinks have become more affordable in almost every corner of the globe - and are likely to become even cheaper and more widely consumed.
It warns without governments taking action to raise prices, global efforts to address the obesity epidemic will be hampered.
Dr Drope and colleagues analysed both real prices and prices relative to income in rich and poor countries around the world from 1990 to 2016, using Coca-Cola as a proxy because it is the most widely available brand.
They found fizzy drinks became cheaper in 79 of the 82, mainly due to a combination of increases in income and decreases in price. Real prices dropped in 56.
Dr Drope said: "Although the increase in affordability is partly due to economic progress that resulted from rapid global economic development, it is also attributable to a lack of action taken by policy makers to affect the price of sugar-sweetened beverages.
"We argue and the scientific literature strongly suggests that this environment of increasingly affordable sugar-sweetened beverages will inevitably drive increased consumption of such products and will certainly hamper global efforts to address the overweight and obesity epidemic."
The authors also reviewed price trends for bottled water and found it is typically more expensive and less affordable than fizzy drinks.
Because rising incomes are a positive sign of growth, Dr Drope added "the logical intervention is for governments to affect prices through excise taxation, as they have done with other unhealthful products such as cigarettes."
Coca-Cola comprised more than a quarter of the global market in fizzy drinks in 2014, more than double its closest competitor.
Last year's British study found despite mounting concerns over childhood obesity and diabetes, supermarkets were slashing prices on branded and own brand colas.
Customers at Tesco and Morrisons were able to buy two bottles of cola - containing four litres together - for 90p. Each two-litre bottle of cola contained a staggering 49 teaspoons of sugar.
Lidl Freeway Cola and Aldi Vive Cola were sold at 42p each for two litres, meaning the maximum sugar intake cost the equivalent of just 4.8p.
While supermarkets are keen to slash prices of cola and other fizzy drinks, bottled water cost far more per litre in contrast.
For example, a 1.5 litre bottle of HIghland Spring sparkling water cost 75p.
Research has shown cutting the amount of sugar in sweetened drinks by 40% could prevent 300,000 cases of diabetes and one million cases of obesity.
In Britain, sugar-filled soft drinks will see a tax hike in April 2018 in an attempt to combat rising levels of obesity. The money raised will go to the Department for Education (DfE) for school sports.
Tax on drinks with more than five grams of sugar per 100ml will be levied by 18p per litre, while those with eight grams or more of sugar per 100ml will have an extra tax of 24p per litre.
It is hoped it will bring significant health benefits, cutting rates of tooth decay, obesity and type 2 diabetes.