A trial found that nuts improve sperm count, vitality, swimming ability and shape - all factors that influence fertility.

Nuts are rich in omega-3 fatty acids, antioxidants and folate, which in other studies have also been found to benefit sperm.

For the 14-week study, 119 healthy young men aged 18 to 35 were randomly assigned to two groups. One ate a normal western diet, while the other consumed the same diet with 60 grams per day of mixed almonds, hazelnuts and walnuts.

Comparing the two groups showed that men who had nuts added to their diet had a 16 per cent higher sperm count, while their sperm vitality was improved by four per cent, motility - swimming ability - by six per cent and morphology (shape) by one per cent.

Men in the nut group also showed significantly reduced levels of sperm DNA fragmentation, which is closely linked to male infertility.

The Spanish authors said the study results were not on their own enough to justify urging men to eat nuts if they want to conceive.

But lead researcher Dr Albert Salas-Huetos, from the University Rovira i Virgili in Reus, said: "Evidence is accumulating in the literature that healthy lifestyle changes such as following a healthy dietary pattern might help conception - and of course, nuts are a key component of a Mediterranean healthy diet."

The findings were presented at the annual meeting of the European Society of Human Reproduction and Embryology (Eshre) taking place in Barcelona.

Australian Associated Press