Fast food may often be high in salt and the exact levels seem to vary by country, according to an international study that looked at fast food menu items in six countries.
Findings published in the Canadian Medical Association Journal showed that, in general, certain foods had less salt in the UK than in the United States or Canada, such as McDonald's chicken nuggets and some chain-restaurant pizzas.
"The salt content of fast foods varies substantially, not only by type of food, but by company and country in which the food is produced," wrote Elizabeth Dunford of the George Institute for Global Health in Australia, who led the study.
"Although the reasons for this variation are not clear, the marked differences in salt content of very similar products suggest that technical reasons are not a primary explanation."
One serving of McDonald's Chicken McNuggets, for example, came with 1.5 grams of salt (600 milligrams of sodium) in the United States and 1.7 grams of salt (680 mg of sodium) in Canada. That compared with just 0.6 grams of salt (240 mg of sodium) in the UK.
The chicken nuggets served in Australia, France and New Zealand had salt levels that fell somewhere in between.
Salt was pervasive regardless of location, though. Overall, fast-food burgers served up an average of 1.3 grams of salt (520 mg of sodium) across all countries with only small national differences.
It's not clear why salt content in some fast food items varied by country, said Norman Campbell of the University of Calgary in Canada, who worked on the study.
One factor, though, could be UK government efforts, the researchers wrote. The UK has set voluntary salt-reduction "targets" for the packaged food industry.
The targets do not yet extend to fast food, but some fast food companies were part of the discussions that helped set the goals, noted Dunford.
"In the right regulatory environment, it is likely that fast food companies could substantially reduce the salt in their products, translating to large gains for population health," she and her colleagues wrote.
The food industry has argued in the past that salt reduction is difficult because it requires new processes and technologies.
A McDonald's spokesperson pointed out that the study used data from 2010.
"We have already reduced sodium by 10% in the majority of our national chicken menu offerings in the US - most recently Chicken McNuggets," the spokesperson said.
"Sodium reductions will continue across the menu and by 2015, we will reduce sodium an average of 15% across our national menu of food choices."
Campbell said the study was not an attack on the fast food industry, noting that country-to-country variations are seen in packaged food and heavy salt use is not unique to fast food.
In the United states, it's estimated that almost 80% of people's sodium intake comes not from their salt shakers, but from the salt that food makers add to their products.
Campbell argued that it's up to governments to rein in sodium levels in the food supply and that a structured, voluntary approach, where the government works with industry to set lower targets, is probably the most feasible.
"We've been badgering people about salt for years, and it's not working," he said.
"They are out there in a sea of fast food and processed foods. We really need to tackle this at a societal level."