Last spring, a group of Australian researchers published a study suggesting that the more fast food and generalized ‘junk’ that women eat, the more difficult it might be for them to get pregnant. In the study, 5,568 first-time mothers were asked to describe their diets in the month before they got knocked up, and eating garbage—our term, not the scientists’—seemed to affect how long it took them to conceive.
The women who “rarely or never” ate fast food had an 8% risk of infertility, while women who ate McMeals four or more times a week were twice as likely to experience periods of infertility. The frequent fast food eaters also took, on average, a month longer to get pregnant than women whose diets were ‘healthier’-in-air-quotes. “Although these dietary components and their relationship to fertility has not been specifically studied in human pregnancies [...] we believe that fast food may be one factor mediating infertility through altered ovarian function,” lead study author Jessica Grieger told Reuters.
And sorry, dudes: It’s not just women. According to new research from Harvard University, eating trash food can affect your fertility, too. In this study, scientists assessed the “diet, semen quality, reproductive hormones, and lifestyle factors” of 2,935 Danish men who underwent medical exams before beginning their military service. (Yes, we also have questions about what “semen quality” has to do with the Royal Danish Army.)
The researchers separated the men by their dietary patterns: the “Western” diet, which was heavy on pizza, processed foods and refined grains, red meat, snacks, candy, and “high-energy drinks”; the Prudent diet consisting of fish and chicken, fruits and veggies, and water; the Smørrebrød, which involved whole grains, cold fish, mayonnaise and other dairy, and cold processed meats; and the Vegetarian, which is self-explanatory, but also included soymilk and eggs.
They soon learned that the men who had both the highest sperm count and the healthiest sperm followed the Prudent diet, while the fewest and worst sperm were produced by those who went with that Western diet. (The Vegetarian diet produced the second best sperm count and quality, followed by the Smørrebrød.)
The scientists also noted that the men on the Western diets had lower levels of a hormone called inhibin-B. That could mean that they had fewer functional Sertoli cells, which would affect their sperm production. There is some debate over whether stressed-out or diminished Sertoli cells can recover—or whether this study could accurately measure that at all. “That’s something that you can’t tell unless you’re looking at testicular tissue from a testicular biopsy," Dr. Bobby Najari, a urologist at NYU Langone Health, told Men’s Health. “Concern about the health of Sertoli cells is taking this data a step too far."
What doesn’t seem to be up for debate is that diet—especially a shitty diet—can have a significant effect on both male and female fertility. The results of this Harvard study haven’t been peer-reviewed yet, but they will be presented at this week’s annual European Society for Human Reproduction and Embryology (ESHRE) conference. “Most men think they’re invincible until their first big health event occurs, which is often either miscarriage or infertility,” ESHRE president Dr. Roy Farquharson told The Telegraph. “Then their partner will quite rightly ask them, ‘What are you doing?’ Because the sperm is just as important as the egg.”
That’s true. It’s also true that we’re way curious about what happens at those Dutch medical exams.
This article originally appeared on VICE US.