The paper said it funded lab tests to examine caffeine levels in popular sodas and found slightly higher levels in Diet Coke compared with Red Coke.
These found that samples of Diet Coke contained 139mg of caffeine/liter compared to 109mg in regular Coke; 46mg per can versus 36mg.
Pepsi also had more caffeine, with the respective per liter caffeine scores for Diet and regular versions 135mg (44.55mg/330ml can) and 122mg, which led the paper to criticize big soda for implying that diet versions are healthier.
Asked if health-conscious consumers didn't prefer less rather than more caffeine, a Coca-Cola spokesperson sent us the following statement.
"Caffeine is used to enhance the flavor of certain carbonated drinks, including Coca-Cola, and adds a slightly bitter taste which helps create a pleasant overal flavor in drinks. The amount of caffeine found in our colas is relatively small - about 30mg of caffeine per 330ml serving," they said.
"There are slightly different amounts of caffeine in different brands to contribute to their distinct flavour profiles. The amount of caffeine in food and drink does vary, whether that be chocolate, coffee or soft drinks. We clearly indicate the amount of caffeine in our drinks on our website and provide an online calculator to give you an idea of the amount you are consuming. We also offer caffeine-free colas for people who want them," they added.
Interestingly, according to the website Death by Caffeine, US Diet Pepsi contains only 35mg/12oz can, while Pepsi Cola contains 38mg (a reverse of the UK situation), although Coca-Cola Classic contains 34mg/12oz can compared with 45mg per can of Diet Coke; UK Diet Pepsi is also significantly stronger than its US peer.