Adding nuts to a healthy diet may help release people from a dangerous combination of health problems.

Up to 25% of people in the UK are thought to have “metabolic syndrome”, which includes obesity and high blood pressure, cholesterol and blood sugar.

A Mediterranean diet of vegetables, fruit and fish plus daily nuts boosted health in more than one in eight at-risk volunteers, a Spanish study found.

The research was published in the Archives of Internal Medicine journal.

The healthy properties of certain kinds of nuts, eaten in moderation, has been noted before.

However, the researchers from the University of Rovira i Virgili in Spain, tested more than 1,200 volunteers with metabolic syndrome to see if adding nuts could boost existing healthy diets.

People with metabolic syndrome are at greatly increased risk of cardiovascular disease.

The group was split into thirds, the first of which were just given advice on low-fat eating.

The next third got quarterly teaching on the Mediterranean diet, which as well as eating plenty of vegetables, cereal crops and fruit, also means cutting down on dairy produce and red meat. They were each given a litre of olive oil a week to supplement this.

The final third got the same teaching, but they were given a 30g bag of mixed nuts every day.

None was told they had to restrict their calorie intake.

After a year, the volunteers were reassessed to see whether their health had improved.

Approximately 2% of the group who were told about low-fat diets had improved to the extent that they were no longer classed as having metabolic syndrome.

Among those following a Mediterranean diet including olive oil, the figure rose to 6.7%.

Finally, 13.7% of those eating their daily bag of nuts as well as the Mediterranean diet had improved.

Even though none of the participants’ weight had dropped significantly over the year, waist circumferences had diminished in the nut-eating group, and cholesterol and blood pressure levels had dropped.

The researchers said that the nuts may have been helping to cut the amount of chronic inflammation linked to their weight.

Dr Jordi Salas-Salvado, the lead author, said: “The results of the study show that a non-energy restricted traditional Mediterranean diet enriched with nuts, which is high in fat, high in unsaturated fat and palatable, is a useful tool in managing metabolic syndrome.”

However, a spokesman for the British Dietetic Association warned that the findings did not give people licence to eat large quantities of nuts in the hope this would improve their health.

“You can’t just sit on the sofa this Christmas and eat nuts – you should be making sure that if you add this many calories to you diet, you should take them out somewhere else if possible.

“And this probably only refers to tree nuts, such as hazelnuts and almonds, rather than peanuts, which aren’t actually a nut at all.

“People should also be careful not eat too may salted nuts, as that certainly is no good for your blood pressure.”