A study in the Canadian Medical Association Journal looked at the salt levels of more than 2,000 food items sold by six major companies in developed countries.
Researchers found large differences, with the UK and France having far lower amounts of sodium in similar products than the US and Canada.
The findings will be welcomed by policymakers in Britain, where efforts are underway to reduce the levels of salt in food, as a high intake of dietary salt is associated with an increased risk of blood pressure.
"We saw marked variability in the reported salt content of products provided by major transnational fast food companies," the study authors confirmed.
"Decreasing salt in fast foods would appear to be technically feasible and is likely to produce important gains in population health."
Earlier this year (March 26th), Consensus Action on Salt and Health warned consumers about the high levels of salt in many takeaway pizzas.
Researchers found that takeaway pizzas contain up to 2.5 times more salt than those purchased in UK supermarkets.