Scientists have theorized a number of potential causes ranging from household chemicals to microplastics. Another possible culprit may be a man's diet.
Now, a cross-sectional study published Friday in the journal JAMA Network Open lends support to the notion that a man's diet seems to directly impact both sperm count and quality.
In order to procure the data for such a study, the researchers began at the source, by rounding up a large group of young men. Specifically, 2,935 young Danish men undergoing a physical screening to serve in the Danish armed forces - a portion of which includes a study of fertility.
The data, collected between 2017 and 2019 included, along with more typical physical measurements such as height, BMI, and blood samples, as well as notes on semen qualities such as overall volume, sperm count, movement, and shape. The researchers also asked participants to disclose their eating habits over the three months prior from a list of 136 different food items.
These items were ranked into four distinct dietary patterns: a Western diet, heavy in red meats, fried food, and sugary drinks; a "prudent" diet, laden with fruits, vegetables, fish, and chick; "vegetarian like," mainly vegetables, eggs, and milk; and a traditionally Danish "open-sandwich" diet.
Comparing dietary habits to data on participant's sperm, researchers found that men with mainly Western diets had the lowest sperm counts, between 109 to 138 million. Of the other three eating styles, "prudent" eaters had sperm which were both healthier and more numerous, averaging 146 to 183 million sperm per load. Although "open-sandwich" eaters had the fastest sperm while "vegetarian like" diets led to the most optimally shaped sperm.
"Dietary factors are necessary for the production of healthy functioning sperm with high fertility potential," study co-author Feiby Nassan, a researcher at the Harvard T.H. Chan School of Public Health, told Inverse. "I believe that it is not only, 'You are what you eat,' but it is also 'Your sperm is what you eat,'" Nassan says.
While the study is a solid start, the researchers also acknowledge more work on the subject can be - and needs to be - done.
To fully understand the implications of diet on a man's fertility similar research should be conducted among populations from different nations. It's also been suggested that individual semen samples may not be entirely reliable (it's not great if a study participant came in spent after a big night out).
While diet does seem correlated to overall sexual health, it isn't the sole factor, the researchers note. Still, diet is something that's easily changed, so there's no reason not to switch up your kitchen routine if you're looking for a scientifically-suggested way to potentially bolster your sperm count.
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