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Two new studies suggest that eating a healthy diet may be linked to stronger and more abundant sperm.

One study found that men who ate more red meat, processed carbs, sweets and energy drinks had reduced sperm motility, compared with men whose diets were heavier in fish, whole grains and fruits and veggies.

In the second study, researchers found that men whose diets were high in trans fats had lower sperm concentration levels than men who ate little or no trans fats.

Both studies, conducted by separate teams at Harvard, were presented Monday at the American Society for Reproductive Medicine in Orlando, Fla.

In the first study, researcher Audrey J. Gaskins, a doctoral candidate at the Harvard School of Public Health, and colleagues analyzed food surveys from 188 healthy men aged 18 and 22. The men’s diets were then compared to the results of semen tests, which measured sperm movement, concentration and shape.

The researchers found no association between diet and sperm count or shape, but found that sperm motility was better in men eating “prudent” diets (rich in fresh produce and whole grains) than those eating “Western” ones (red meat and processed grains). The results are intriguing, but they don’t prove that diet influences sperm movement; lots of factors may affect semen quality.

“This was a small study, and we don’t know if there’s something else about the men that causes them to have worse motility,” Gaskins told HealthDay. “We don’t know if nutrition actually causes the change. So, for now all we can say is that there’s an association between nutrition and sperm quality.”

In another presentation, Dr. Jorge Chavarro, an assistant professor of nutrition epidemiology at the Harvard School of Public Health, reported on analyses of diet and semen quality in 100 men attending a fertility clinic. The researchers found that the association between higher trans fat intake and lower sperm count held, even after controlling for other factors such like age, weight, drinking and smoking status, caffeine intake and total calories consumed. But diet had no impact on sperm movement or shape, and the researchers noted that the men who had lower sperm concentrations in their study were still within normal.

“We are starting to get a better idea of how nutrition affects fertility, but we still have a lot to learn,” Chavarro told MedPage Today.

Neither study has been peer reviewed, so these results must be considered preliminary until they are published in a journal. The moral of the story, at least for now: a junk food diet is bad for you — possibly in more ways than you thought.

Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.