Revealed: the salads that contain more salt than crisps

This is not just a salad – it's a Marks & Spencer salad, and it contains five times more salt than a packet of crisps.

Usually regarded as a healthy option by workers popping out of the office for lunch, many salads sold on British high streets have potentially harmful levels of salt, research has shown.

Only 2 per cent of 268 salads checked at shops, cafés and fast-food chains had less than the 0.5g salt contained in a bag of Walkers crisps. One in 10 had more salt than the 2.1g found in a McDonald's Big Mac.

Marks & Spencer had seven of the 10 saltiest supermarket salads. Its Taste of Asia product was found to contain 2.8g of salt – the equivalent of eating more than five bags of crisps in a single sitting.

Excessive salt consumption can lead to heart attacks and strokes, and the Food Standards Agency recommends no more than 6g a day for adults.

Consensus Action on Salt and Health (Cash) estimates that at least 15,000 people in the UK die early each year as a result of eating too much salt, most of which is consumed through processed foods. Previously Cash's concern has centred on major dietary sources of salt such as bread and breakfast cereals, but its latest survey found heavy salting of salads by sandwich shops, fast food chains and supermarkets.

The spicy crayfish noodles at EAT, a sandwich chain, contained 3.5g per portion, more than half an adult's recommended maximum in a single salad. Pret A Manger's super houmous salad had 3.2g of salt, while, among KFC salads, the Zinger had 3.1g and the original chicken 2.9g.

At supermarkets, Cash found that average salt levels in salads had fallen by 23 per cent, from 1.64g to 1.26g a portion, since it did its last survey five years ago. But some salads, including many so-called "healthy options", still had high levels. Marks & Spencer made three of the five saltiest shop salads, including its Taste of Asia (with 2.8g per 258g portion), chicken pasta with bacon (2.65g salt per 380g portion) and avocado and feta (2.40g salt per 320g portion).

Only 22 per cent of salads branded as "healthy" would receive a green traffic-light label on salt from the Food Standards Agency. The least salty salad of all was Pret A Manger's No Bread Tricolore with a balsamic vinegar dressing, which contained 0.2g salt.

As well as putting shoppers at risk of heart disease, Cash warned that salty salads could lead to a bloated feeling. "Many women choose salad as a healthy and convenient lunch, particularly when watching their waistline," said Katharine Jenner, its campaign manager.

"Rather than feeling healthy however, they often feel bloated and sluggish – symptoms of water retention which can be caused by the hidden salt in these salads. In the long term the health problems are more serious as salt intake is linked to osteoporosis and high blood pressure."

Professor Graham MacGregor, of the Wolfson Institute of Preventive Medicine and chairman of Cash, said: "It is absurd that only six salads contain less salt than a packet of crisps. Clearly the manufacturers still have a long way to go if we are to reduce our salt intake to 6g a day and save the maximum number of lives."

Cash recommends that salad buyers avoid salty ingredients such as ham, bacon and cheese, and use only some of the pot of dressing.

The British Heart Foundation characterised the survey's findings as worrying. "While it's encouraging that some products have been reformulated since the last survey in 2005, we clearly need to go further to give people a broader choice for lunch on the go with options that are healthy in terms of salt as well as calories, fat and sugar," said Victoria Taylor, its senior heart health dietitian.

Marks & Spencer said the survey has given a misleading picture of the healthiness of its salads. A nutritionist at the company, Claire Hughes, said: "Unfortunately Cash's survey makes comparing salt levels in salads very confusing for consumers as their survey looks at different pack sizes. We always provide front of pack colour-coded labelling and are committed to continuing to review the salt in our products, whilst still offering a broad range of cuisines for our customers to enjoy."