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Study Finds No Significant Difference in Sperm Quality Between Vegetarians and Omnivores

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There is no discernible difference in sperm quality or sex hormone levels between vegetarians and omnivores, according to a recent systematic review and meta-analysis by researchers from Alborz and Tehran University of Medical Sciences. The findings were published in the Journal of Human Nutrition and Dietetics.

A rising number of individuals are adopting vegetarian diets for health, environmental, and ethical reasons. While the beneficial effects of vegetarian diets on metabolic diseases are well-documented, their impact on reproductive health remains less clear. To address this gap, researchers Parham Samimisedeh, Elmira Jafari Afshar, Hanieh-Sadat Ejtahed, and Mostafa Qorbani undertook a comprehensive analysis to determine the possible association between vegetarian diets and fertility, particularly focusing on sperm quality and sex hormone levels.

The researchers systematically searched online databases, including PubMed, ISI, Scopus, and Google Scholar, up to 1st December 2022, using relevant keywords. They included observational studies that compared semen quality, sex hormone levels, and infertility in people adhering to vegetarian diets versus those on omnivore diets. I2 and Q tests were used to see if the studies were heterogeneous, and standardised mean differences (SMD) were found to compare the results between the two groups.

Out of 972 retrieved documents, 20 articles met the inclusion criteria, with 16 being eligible for quantitative synthesis. The study focused on several key indicators, including total sperm count, total and progressive sperm motility, sperm morphology, and sperm concentration.

The meta-analysis results indicated no significant differences between vegetarians and omnivores concerning semen quality parameters, such as total sperm count, total and progressive sperm motility, sperm morphology, and sperm concentration. The pooled SMDs for these parameters showed non-significant differences, suggesting that adherence to a vegetarian diet does not adversely impact sperm quality.

Regarding sex hormone levels, the study found that male vegetarians exhibited significantly higher levels of sex hormone-binding globulin (SHBG) compared to omnivores. But there were no significant differences in other sex hormone parameters, including plasma total testosterone, E2 (oestradiol), and prolactin. For female sex hormones, the only significant difference was the lower level of plasma oestrogen (E1) in vegetarians compared to omnivores.

Despite the numerous health benefits associated with vegetarian diets, the study suggested that there are no conclusive positive or negative associations between vegetarian diets and semen quality, sex hormone levels, or infertility. The findings align with previous research indicating that diet alone may not be a determining factor in fertility outcomes.

Several studies have suggested that healthier diets, such as the Mediterranean or prudent diets, are associated with better semen quality and strengthened fertility. Conversely, high-caloric Western diets, characterised by the consumption of processed red meat, trans- and saturated fatty acids, fast foods, sugar, and refined grains, have been linked to poorer sperm parameters.

The potential benefits of vegetarian diets on sperm and semen quality include higher consumption of antioxidants, polyphenols, and carotenoids, which can reduce oxidative stress and DNA damage in sperm. Additionally, vegetarians typically have lower body mass index (BMI) levels, reducing the negative impact of obesity on sperm function.

But vegetarian diets also pose certain risks, primarily related to micronutrient deficiencies. Vegetarians may lack essential nutrients such as vitamin B12, vitamin D, calcium, zinc, iron, and essential fatty acids, all of which are crucial for maintaining optimal sperm quality and overall reproductive health.

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