A diet high in saturated fat has been associated with a reduced sperm count.
A study of 99 men who were attending an American fertility clinic discovered that those on junk food diets had poorer sperm quality.
Increased intakes of omega-3 fatty acids, which are found in fish and plant oils, are related with higher sperm concentration.
The team from Harvard Medical School in Boston questioned men with regard to their diet and analysed sperm samples over four years.
In stark contrast to those eating the least fat, men who had highest fat intake had a 43% lower sperm count and 38% lower sperm concentration.
These findings strengthen the case for a healthy diet having benefits for male fertility as well as being general sound health advice.
Men who ate the most omega-3 fatty acids had sperm with a more normal structure than men those with the lowest intake.
71 per cent of the participants were overweight or obese which may have had an impact on sperm quality.
Further research is needed to confirm the findings.
Moreover, the research was conducted with a small number of participants; further research would need to study far greater numbers of men for the same purpose.