Eating a walnut-enriched diet with 75 grams of walnuts every day may improve sperm vitality (movement) and morphology (form) -- markers of semen quality, which is a predictor of male fertility -- in men who added walnuts to their diet compared to men who did not, a study has found.

The findings showed that mice that consumed a diet containing 19.6 per cent of calories from walnuts (equivalent to about 2.5 ounces per day in humans) had significant improvements in sperm quality by reducing lipid peroxidation -- a process that can damage sperm cells.

"The study found that eating walnuts can actually help improve sperm quality, likely by reducing peroxidative damage in sperm cells," said lead researcher Patricia A. Martin-Deleon from the University of Delaware in Newark, US.

Cell damage harms sperm membranes, which are primarily made up of polyunsaturated fatty acids (PUFAs).

However, eating walnuts, the only tree nut that are predominantly comprised of PUFAs, may help reduce that damage as one ounce of walnuts contain 13 grams of PUFAs out of 18 grams of total fat, the researchers said. 

"The findings suggest that walnuts may be beneficial for sperm health," Martin-Deleon added.

For the study, the team took healthy male mice as well as mice that were genetically predetermined to be infertile (Pmca4-/- gene deletion) were randomly assigned to a walnut-enriched diet or a control diet without walnuts that was followed for 9-11 weeks.

Among the mice that consumed walnuts, fertile mice experienced a significant improvement in sperm motility and morphology and the infertile mice had a significant improvement in sperm morphology. 

Both groups experienced a significant reduction in peroxidative damage. However, investigators were unable to reverse the adverse effects on sperm motility in the infertile mice because of the genetic deletion in this group.