Walnuts are top of the tree when it comes to heart-healthy superfoods, research has shown.
The Christmas favourite is packed with more potent and abundant antioxidants than any other popular nut, as well as healthy fibre, protein, vitamins and minerals.
A meta-analysis of walnuts by Harvard scientists found diets rich in walnuts can significantly reduce cholesterol levels, supporting growing evidence to suggest these popular nuts can improve healthy blood lipid ratios.
Tree and ground nuts are generally said to be among nature's most perfect ready-made foods.
As well as having all the nutritious elements necessary for a healthy diet, they also contain high levels of protective antioxidants which counter the effects of harmful molecules.
Diets containing two percent, six percent, or nine percent walnuts, when given to old rats, were found to reverse several parameters of brain aging, as well as age-related motor and cognitive deficits, says James Joseph, PhD, of the U.S. Department of Agriculture Human Nutrition Research Center at Tufts University in Boston.
Research suggests regular consumption of nuts can reduce the risk of heart disease, certain cancers, and type-2 diabetes.
But until now it was not known which had the most health-giving properties.
To answer this question, scientists analysed the antioxidant content of nine different types of nut: walnuts, almonds, peanuts, pistachios, hazelnuts, Brazil nuts, cashews, macadamias and pecans.
Study leader Dr Joe Vinson, from the University of Scranton in Pennsylvania, US, said: 'Walnuts rank above peanuts, almonds, pecans, pistachios and other nuts.
'A handful of walnuts contains almost twice as much antioxidants as an equivalent amount of any other commonly consumed nut. But unfortunately, people don't eat a lot of them.
'This study suggests that consumers should eat more walnuts as part of a healthy diet.'
Dr Vinson's team found that walnuts not only had more antioxidants than other nuts, but more powerful antioxidants.
Those in walnuts were between two and 15 times more potent than vitamin E, renowned for its antioxidant properties.
The findings were presented today at the 241st national meeting of the American Chemical Society in Anaheim, California.
Dr Vinson said another advantage of walnuts was that they were usually eaten in their natural state, rather than being roasted.
'The heat from roasting nuts generally reduces the quality of the antioxidants,' he added.
Nuts account for just eight per cent of the daily antioxidant consumption in an average person's diet.
Dr Vinson said many people were put off nuts because they were thought to be fattening. But he pointed out that nuts generally contain healthy polyunsaturated and monounsaturated fats rather than artery-clogging saturated fat.
Eating nuts did not appear to cause weight gain and might even reduce over-eating by making people feel full.
Around seven walnuts a day was the right amount to eat to get the maximum health benefit, said Dr Vinson.