Eating a pack of walnuts a day significantly improves sperm quality and may boost fertility in men, scientists claim.

Researchers found that eating 2.5 ounces (75 grams) of walnuts a day improved the vitality, motility and morphology of sperm in healthy men aged 21 to 35.

An estimated 70 million couples around the world experience subfertility or infertility, with the male partner accounting for 30 percent to 50 percent of these cases.

Previous research suggests that semen quality in humans has declined rapidly in industrialized nations, possibly due to pollution, poor lifestyle habits and an increasingly fattening Western-style diet.

Dr. Wendie Robbins and her colleagues at the University of California, Los Angeles researched whether increasing the consumption of walnuts, which are rich in polyunsaturated fatty acids (PUFAs) that are essential for sperm maturation and membrane function, would increase sperm quality in men on a Western-style diet.

Other foods rich in polyunsaturated fatty acids include fish and fish oil supplements, flax seed, and walnuts, which are also rich sources of α-linolenic acid (ALA), a plant-derived source of omega-3.

The study involved 117 healthy men between the ages of 21 and 35 who ate a Western-style diet. Researchers divided the men into two groups, the control group, which consisted of 58 men, was instructed to avoid eating tree nuts and the experimental group of 59 men was instructed to eat 75 grams of walnuts a day.

Past studies found that consuming 75 grams of walnuts is just the right amount to change blood lipid levels without weight gain. 

Researchers analyzed the men's semen quality and measured the conventional factors that predict male fertility, including sperm concentration, vitality, motility, morphology, and chromosome abnormalities before the experiment began and then again 12 weeks later.

While there was no significant changes in body-mass index, body weight, or activity level in the control or experimental group after 12 weeks, men who ate walnuts had significantly increased levels of omega-6 and omega-3 fatty acids and showed improvement in sperm vitality, motility, and morphology.

Researchers found that the men in the walnut group also had fewer chromosomal abnormalities in their sperm after the walnut dietary intervention. The control group showed no improvement in sperm vitality, motility, and morphology or reduced chromosomal abnormalities in their sperm.

Researchers noted that while the latest findings suggest that eating 75 grams of walnuts per day can positively affect a young man's sperm quality, they are unsure as to whether the benefits would apply to men with existing fertility problems and whether eating more walnuts would actually directly cause increased fertility.