New research shows that a Western-style diet can permanently kill off sperm-producing cells by age 18.

Infertility in males is something that most people assume happens later in life, once a man has reached his 30s, 40s, and beyond. But new research from Harvard University shows that irreversible damage can happen much earlier in life, particularly if a young man eats a junky Western-style diet.

By age 18, if a young man has eaten a significant quantity of high fat and processed foods such as pizza, chips, and snacks, he may have killed off sperm-producing cells that can never be replaced. The Telegraph reports,

"Experts believe processed food starved of antioxidants places sperm-producing cells under 'oxidative stress', ultimately killing them."

This research was based on data collected from 3,000 young Danish men who were entering the military. They underwent medical examinations and were asked about their dietary habits. Based on their responses, four kinds of diets were revealed – vegetarian (vegetables, eggs, soy milk), Western (red and processed meats, fats, sugars, sweetened and energy beverages, refined grains), 'prudent' (chicken, fish, vegetables, fruit, water), and 'Smørrebrød' (cold processed meats and fish, whole grains, dairy).

When the men's sperm was analyzed for volume, motility, and concentration, those following the prudent diet had the highest sperm counts. Next were the vegetarian and Smørrebrød adherents. Those with a Western diet had the lowest counts.

While lifestyle changes can improve sperm health within two to three months (and men are certainly encouraged to do this when preparing for a pregnancy, as the quality of sperm is just as important as a woman's egg), scientists believe that the sperm-producing cells, known as Sertoli cells, cannot be repaired once damaged.

This is alarming news, and hopefully young men will feel motivated to clean up their diets when presented with this information. As lead researcher Jorge Chavarro said, young men are sensitive about things that could affect sperm count because "it's a perceived measure of masculinity." So if the threat of weight gain, low energy, or overall poor health are not enough to shake up one's eating habits, perhaps this study will do it.