E Experts believe that antioxidant-starved processed foods expose sperm-producing cells to "oxidative stress" and ultimately kill them.
Professor Allan Pacey of the University of Sheffield, one of the leading authorities for sperm, said: "This only shows the power of nutrition in terms of how the testes work.
"The worry would be that a poor diet that is younger will cause a change that stays with you."
Harvard researchers accessed data from nearly 3,000 men when joining the National Service Danish forces were subjected to a medical examination.
The average age was 1
Four diets were identified from responses to a nutritional questionnaire: a "western" diet marked by a red mark Meat, Processed Meat, Fatty and Sugary Foods and Beverages; a "prudent" diet, comprising mainly chicken, fish, vegetables and fruits; a smørrebrød diet with cold processed meat, whole grains, mayonnaise, cold fish, spices and dairy products; and a traditional vegetarian diet with lots of vegetables, soy milk and eggs.
Sperm health, measured in terms of concentration, volume and flexibility, was best with a cautious diet, followed by a vegetarian and a smørrebrød diet. Those who followed a western diet achieved the worst results.
The scientists also ran hormone tests that pointed to the health of sperm-producing Sertoli cells, and found again that they were used up in the young men who favored junk food.
While a It is believed that a person can improve their sperm health over time by improving their diet.
This affects the amount of sperm that they can produce at the same time.
Dr. Jorge Chavarro, who led the research, said the perceived threat to the masculinity of young men could make them eat healthier. This could affect the sperm count, as it is a perceived measure of masculinity.
The research results will be presented at the annual conference of the European Society for Human Reproduction and Embryology (ESHRE) in Vienna.
They came as scientists demanded that men with a poor diet be examined for DNA damage to their sperm.
DNA damage is a factor in up to half of miscarriages.
In the meantime, Dr. Roy Farquharson, an NHS Adviser and President of ESHRE, said: "Most men think they are invincible until their first major health event occurs, which is often miscarriages or infertility.
"Then her partner will rightly ask her, 'What are you doing? # Because the sperm is just as important as the egg.
He said lifestyle improvements could improve sperm quality within two to three months, and autumn, which could be associated with hours of daylight during those months, and the fact that men tend to do more sports.