A fistful of walnuts a day may help to keep the fertility doctor away, new research suggests.
Eating 75 grams of the nuts daily was found to improve the health of sperm in men aged 21 to 35.
Scientists in the US split 117 healthy volunteers into two groups, one of which had walnuts added to their diet.
The nuts are rich in a natural plant source of omega-3, a type of fatty acid thought to be critical to sperm development.
Researchers tested various indicators of the quality of participants' sperm.
At the end of three months, men consuming walnuts had significantly increased levels of omega-6 and omega-3 fatty acids in their blood.
Their sperm also showed across-the-board improvements in concentration, vitality, motility (movement), and morphology (shape).
Walnut-eaters also had fewer chromosomal abnormalities in their sperm.
The research, led by Dr Wendie Robbins from the University of California at Los Angeles, is reported in the journal Biology of Reproduction.
However, despite the improvements, it is still not known whether eating walnuts can actually help men with fertility problems.