Salt hiding in everyday foods such as bread and sausages may be driving up obesity rates, a study suggests. Researchers looked at survey data from almost 5,000 people and gathered urine samples from 558 men and 702 women. Men with the highest levels of sodium in their urine were six times more likely to be obese than those with the lowest levels. For women, risk increased by almost five times.

Annika Santalahti, of the Finnish Institute for Health and Welfare in Helsinki, Finland, said the stronger trend in men may be because “men consume more food, and also more of foods that are the main food sources of sodium in the diet, such as meat products, bread and bakery products, and cheese”.

She added: “Contrary to popular belief, high sodium intake is not mainly caused by unhealthy foods, but by ordinary everyday food.

“In Finland, most sodium is obtained from processed meat products, bread and dairy products, especially cheese.”

The study found that participants' average salt intake exceeded the World Health Organisation’s recommendation of 5g or less per day.

Those with the highest intake ate twice as much salt as those with the lowest. The researchers said further work was needed to understand how salt may influence obesity risk.

Possible explanations include changes in the secretion of satiety hormones as a result of long-term exposure to a salty diet. Salt intake may also be an indicator of worse overall nutrition, such as eating too much ultra-processed, high-sodium food.

The researchers added: “In our view, the food industry plays a significant role in reducing the population's sodium intake, as the majority of food consumption comes from sources other than unprocessed primary production.

“It is important to pay attention to how salty commonly consumed daily foods are, as these account for a large proportion of the daily sodium intake.

“Of course, general changes in the food environment also play a role, such as whether food is prepared at home or consumed in restaurants or as takeaway food.”

The UK has had a voluntary salt reduction programme scene 2004, which encourages the food industry to reduce the salt content of products. Adults are recommended to eat less than 6g per day but the average UK adult eats around 8.1g per day.

The findings will be presented at the European Congress on Obesity in Spain in May.