A study published in the Archives of Internal medicine journal showed that a Mediterranean diet of fruit, vegetables, fish and nuts daily boosted health and reduced metabolic syndrome in the volunteers tested. The diet consisted of eating a handful of hazelnuts, walnuts and almonds as well as adding olive oil to the diet, and restricting intake of dairy produce and red meat.

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."

Nuts are one of the best plant sources of protein. They are rich in fibre, phytonutrients, and antioxidants and are a great source of polyunsaturated fats. However, nuts do have a high calorific content, so if a lot of nuts are added to the diet then calorie intake should be reduced elsewhere.