The quality of sperm was also improved among those who took brisk walks, compared with
those who either did little physical activity or went running.
The three papers, presented at the annual meeting of the
American Society of Reproductive Medicine in Florida, highlight the
importance of the lifestyle of a prospective father as well as that
of their female partner in determining hether or not they can have a
baby.
In the first study, researchers at the Harvard School of Public Health looked at what 188 students ate and drank.
They divided their diets into a "prudent" one characterised by high
intake of fish, fruit, vegetables and pulses, and a "western" one full
of pizza, red and processed meat, high energy drinks and snacks.
Those with the best diet had 11 per cent more motile sperm - better at
swimming towards an egg - than those with the least healthy eating
habits. Lead researcher Audrey Gaskins said: "Motility is most important for couples who want to try to conceive naturally. A small increase could lead to a small increase in fertility."
A separate study at Harvard analysed the diet of 99 men who were already attending a fertility clinic because they and their wives or girlfriends were unable to get pregnant.
Academics found that consumption of Trans Fatty Acids - previously found in many fried fast food joints but now being phased out - was linked to sperm concentration.
Men who took 1.3 per cent of their calories from trans-fats had on average 48million sperm per millilitre of semen, compared with 79m among those who had consumed just 0.7 per cent of their calories in the form of the fat.
Dr Allan Pacey, a fertility expert at the University of Sheffield, commented: "The influence of a man's diet on his semen quality has been of interest for some time.
"For example, there is now good evidence from a variety of studies that men with a higher antioxidant intake have slightly better semen quality and are more likely to become fathers than men who don't. Similarly, there are also studies showing that men who consume key nutrients, ejaculate better sperm.
"Therefore the results of this study, comparing a Western diet with one which is more 'Mediterranean', is not really a surprise and nicely illustrates that a good diet is of benefit when trying to conceive."
A third paper, carried out at the Yamaguchi University School of Medicine in Japan, compared sperm motility among 215 men after analysing how much physical activity they did in an average week.
It found that those who did moderate exercise, such as brisk walking, had better swimming sperm than both those who did little physical activity and those who did strenuous activities.
Dr Pacey said: "There are a number of studies which have examined the relationship between physical exercise and semen quality, often with contradictory results.
"Therefore we have an unclear picture about what effect exercise plays in male fertility, if any.
"We know that obesity and poor diet can reduce sperm production so perhaps in this study we are seeing the positive effects of healthy living as much as we are seeing the benefits of exercise."
