Unhealthy diet associated with poor semen quality

Unhealthy eating, like that associated with the Western diet, is associated with notably worse semen quality and less favorable testicular function than healthier eating patterns, according to a study of nearly 3,000 young Danish men published in JAMA Network Open (2020; 3:e1921610).

Researchers at Harvard T.H. Chan School of Public Health, Boston performed a cross-sectional study of men in Denmark (median age, 19 to 20 years) who didn’t know their fertility status and had filled out a validated food frequency questionnaire. The authors assessed semen quality and concentrations of total and free testosterone, estradiol, inhibin B, follicle-stimulating hormone, luteinizing hormone, and sex hormone-binding globulin. They also studied testicular volume.

“This study is the largest study to date to examine diet pattern with men’s testicular function,” said study co-author Feiby Nassan, ScD, MBBCH, MSc, a research associate at the Harvard T.H. Chan School of Public Health who worked on the study with Niels Jørgensen, MD, PhD, and colleagues.

Decline of semen quality is a growing concern in men around the world. Total sperm count among men in Western countries fell by 50% to 60% from 1973 to 2011, according to a meta-analysis of 185 studies published in Human Reproduction Update (2017; 23:646-59).

Why this is happening is a topic of debate. And while authors are looking at environmental exposures, such as pollution, and behavioral factors, such as smoking and alcohol consumption, they say few have looked at diet quality as a possible cause.

Dr. Nassan and colleagues identified four popular dietary patterns: the largely unhealthy Western diet, with staples such as pizza, processed and red meats, refined grains, and sweets; the generally healthy prudent diet, emphasizing fish, chicken, vegetables, fruit, and water; the traditional Danish open-sandwich pattern, featuring consumption of cold, processed meats, whole grains, mayonnaise, cold fish, condiments, and dairy; and a vegetarian-like pattern, which avoids red meat and chicken and emphasizes vegetables, soy milk, and eggs.

They found that men consuming a Western diet had the lowest total median sperm count at 122 million. Men consuming foods associated with the prudent pattern had the highest median total sperm count at 167. Median sperm counts were 151 million for the vegetarian-like and 146 for the open-sandwich patterns.

Average sperm counts varied within the categories. For example, men in the highest quintile of Western diet consumers had an average 26 million sperm count lower than men in the lowest quintile of Western diet eaters. And those that adhered most to the prudent pattern, the highest quintile, had an average 43 million more sperm than prudent eaters in the lowest quintile.

Men who highly adhered to the open-sandwich pattern had higher counts of motile spermatozoa, while those who consumed a vegetarian-like pattern were more likely to have more morphologically normal spermatozoa compared to men in other dietary categories. Further, men in the highest quintile of Western diet consumers had lower serum inhibin B concentrations and ratios of inhibin B to follicle-stimulating hormone than men in the lowest quintile of Western diet eaters.

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“The hormone results are difficult to explain. Men who had the highest adherence to the Western pattern had higher testosterone concentrations, compared with men with less adherence. But they also had the highest estradiol concentration with unchanged luteinizing hormone levels,” Dr. Nassan said. “This could be due to increased aromatization of testosterone to estradiol and could have resulted in increased negative feedback at the hypothalamic level. If this is correct, this might also explain why follicle-stimulating hormone was not sufficiently higher as a compensation for the lower inhibin B concentration.”

The authors speculated that adherence to the Western diet pattern, at least in part, could lead to reduced hypothalamic activity, which could explain the observed reduction in spermatogenesis, according to Dr. Nassan.

“In addition to this possible explanation, the lower ratio of inhibin B to follicle-stimulating hormone, itself, could also explain a direct adverse effect on the testicles,” she said.

A take-home for urologists, according to Dr. Nassan, is that it may be useful for men’s fertility to follow a generally healthy diet with higher intake of fish, chicken, vegetables, fruit, and water, while cutting back on pizza, French fries, processed and red meats, snacks, refined grains, high-energy drinks, and sweets.

“Patients usually come to your clinics asking those questions about what they should eat and what they should avoid to boost their fertility. Peer-reviewed evidence is limited to answer these questions. This study provides some evidence of the benefits of the generally healthy diet patterns that you could advise your patients to follow-especially the ones whose fertility may need a nudge and may benefit from such diets,” she said.

A limitation of the study is its cross-sectional design, as the authors cannot imply causation from the work.

“However, this does not mean that this association is not important. Many scientific groups, including ours, are working to further study the role of diet and environment on fertility. However, I do not think we have to wait until the perfect controlled blinded clinical trial to happen until we change behavior. In addition, many other studies have suggested consistent results with other health outcomes, so we really have little or nothing to lose if we follow a generally healthy diet,” Dr. Nassan said.