Saturated fats, like those found in rich cheeses and meats, may do more than weigh men down after a meal - a new study also links them to dwindling sperm counts.
Researchers found that young Danish men who ate the most saturated fats had a 38% lower concentration of sperm and a 41% lower sperm count than those who ate the least fat.
"We cannot say that it has a causal effect, but I think other studies have shown that saturated fat intake has shown a connection to other problems and now also for sperm count," said Tina Jensen, the study's lead author from Rigshospitalet in Copenhagen.
The new research is not the first to connect diet and other lifestyle factors to sperm production and quality.
How the study was done
In 2011, Brazilian researchers found eating more grains was associated with improved sperm concentration and motility, and fruit was also linked to a speed and agility boost in sperm.
But that study and most others looked at these associations in men seeking fertility treatments, which may not be representative of all men.
For the new study, Jensen and her colleagues studied 701 young Danish men who were about 20 years old and getting checkups for the military between 2008 and 2010.
They were asked about the food they ate over the prior three months, and then asked for a semen sample.
Jensen told Reuters Health the young men's main motivation to participate in the study was the $85 it paid - not to see if they were fertile.
The researchers then stratified the men into four groups, depending on how much of their energy intake came from saturated fats.
The men who got less than 11.2% of their energy from saturated fats had an average sperm concentration of 50 million per mL of semen and a total sperm count of about 163 million.
That compared to 45 million sperm per mL and a 128 million count in men who got more than 15% of their energy from saturated fats, the researchers reported online December 26 in The American Journal of Clinical Nutrition.
The World Health Organization defines anything over 15 million sperm per mL as normal. In the study, 13% of men in the lowest-fat group and 18% of men in the highest-fat group fell below that level.
Although the study cannot determine whether other lifestyle factors might account for the link, Jensen said her team's findings may partially explain studies that have found sperm counts decreasing around the world.
Last year, French researchers reported that the number of sperm in one mL of the average 35-year-old Frenchman's semen fell from about 74 million in 1989 to about 50 million in 2005 (see Reuters Health story of Dec 4, 2012).
"I think obesity is another cause, but (saturated fats) could also be a possible explanation," she said.
Jensen said that the next step is to find the mechanism by which saturated fat could influence sperm count, and then to see whether sperm counts improve when men cut down on saturated fat in their diets.
Until then, she said it's still too early to tell men with low sperm counts to cut back on saturated fat, but added it's still probably a good idea since it's also linked to other problems, such as heart disease and cancer.
(Reuters Health, January 2013)
Saturated vs. unsaturated fats