Shoppers are being misled about salt content in some foods because the information on labels is based on unrealistic portion sizes, according to new research.

A study of 831 products suggests that manufacturers may be reducing serving sizes deliberately to keep the salt content as low as possible. That on a pack of chicken nuggets, for example, suggested a serving size of 15g (0.53oz) — the equivalent of only one nugget.

Slices of bread — described as one serving on packs — range from 20g to 50g, depending on the loaf, with the corresponding increase in salt. Baked beans portions varied from one half to a third of a 420g can; tomato sauce from 10g to 30g.

The survey, on behalf of the the Local Authorities Co-ordinators of Regulatory Services (Lacors), tested food on sale in supermarkets in 60 council areas across the UK. Geoffrey Theobald, its chairman, said: “There is concern that some customers are being hoodwinked and misled by some manufacturers who are deliberately quoting unreasonably small portion sizes on their packaging to mask the true salt content of their products.”

He added: “It would make it much easier for the consumer to make informed choices if the information was presented in a meaningful way.”

Lacors is now calling for the standardisation of portion sizes for different product types to prevent confusing shoppers and is also demanding that sodium content per 100g should be shown on all packs of processed foods.

Testing showed that overall salt content of foods had dropped by 11 per cent since May 2005, when the last research was conducted. But less than half of all products tested still failed to meet salt reduction targets from the Food Standards Agency, which should be achieved by 2010.

Among the saltiest samples were noodle snacks, with one in five containing more than 4g of salt per serving — two-thirds of the recommended daily intake of 6g.

Significant reductions have been made in meat pies, sausages and biscuits, however.

The Food Standards Agency is also concerned about misleading portion sizes on food labels. It said: “For this reason the agency’s traffic light front-of-pack labelling approach is based on consistent criteria making it easier for shoppers to compare products.

“In cases where there is no traffic light labelling we would advise consumers to check salt levels per 100g and choose the product with the lowest amount.”

The Food and Drink Federation, which represents manufacturers, denied that consumers were being misled. It said: “Far from hoodwinking, we are introducing some of the most open and honest labelling in Europe. Not only do we clearly declare salt levels on the back of pack, many manufacturers are also putting this information on the front of pack, as part of the Guidance Daily Amount labelling schemes.”

Health campaigners Consensus Action on Salt and Health (Cash) is also concerned about the varying portion sizes that mask salt content. Joanna Butten, its nutritionist, said: ”Unrealistic portion sizes, such as one chicken nugget, make the salt per portion information misleading for consumers.”

Cash estimates that if average adult salt consumption wer reduced to 6gs a day it would prevent 70,000 heart attacks and strokes a year.

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