Young men who eat a mainly "Western" diet of pizza, chips and burgers may end up with drastically lower sperm counts.
A study of almost 3 000 men aged 18 to 20 found those with a diet packed with processed meat, pizza, sugary drinks and snacks have worse-quality sperm than those who eat healthily – and suggests some of the damage may be permanent.
Most previous research on diet and fertility has focused on older couples trying to get pregnant, rather than the effects on the sperm of healthy young men. This study found vegetarians have higher sperm counts, as do those whose diets include fish and whole grains, making them more fertile.
Allan Pacey, a professor of andrology – the study of diseases and conditions specific to men – at the University of Sheffield, said: "This just shows the power of diet to the way that testicles function.