Men are more likely to have small testicles and a low sperm count if they eat junk food, a study has found.
Research shows those who eat a diet rich in fish, chicken, fruit, veg and water produce the most sperm and have the biggest testicles.
Eating processed foods and red meat has the opposite effect, Harvard University found.
The findings come after researchers analysed the health and diet of 2,935 men with an average age of 19 during military service entrance exams.
The men’s testicle size was measured and the number, shape and swimming abilities of their sperm was also analysed, The Sun reports.
According to study leader Dr Feiby Nassan, men can boost their chances of becoming a dad by eating a balanced diet.
She added: “Adherence to generally healthy diet patterns was associated with better semen quality, with potentially more favorable fertility potential among adult men.”
The study findings, published in the journal JAMA Network Open, show vegetarians typically ranked second when it comes to measuring testicle size and sperm.
Those on a Scandi diet of dairy and smoked fish come in third, with junk food addicts last.
Men with a healthy diet averaged 167million sperm per load and a testicle volume of 13.7ml.
Those who regularly ate processed foods and red meat averaged just 122million and 13.1ml.
Every man who participated in the study was Danish and underwent the medical test as part of a fitness check for military service.
Last June, it was reported that eating a diet of junk food reduces the fertility of men aged 18 to 20.
The sperm counts of those who ate pizzas, burgers and chips were 26 million lower than those on a “healthy” diet, US scientists found.
The findings suggested red meat, bread and sugary drinks lowered their sperm counts. The hormone levels in men who ate more junk food suggested the cells which produced the sperm were permanently damaged.
Fertility expert Prof Allan Pacey, of Sheffield University, said: “With pizza, chips and red meat we know antioxidant stress goes up and that is bad for sperm.”