The internet loves a good story on alleged health hazards of vegan diets. This week, it’s all about how vegan and vegetarian men have low sperm concentrations. The alarming research is from Loma Linda University, and it was presented at the annual meeting of the American Society for Reproductive Medicine(1).

Should you be concerned about the fact that the vegetarians and vegans in this study had sperm concentrations that were lower than those of the meat-eaters? I don’t think so for a number of reasons.

First, this research has not been published, and it may not yet have gone through any type of peer review. And the abstract is short on details that will be important in that review. Like whether or not the authors controlled for exercise, age, smoking, and other factors that affect sperm concentration. Until more information is available, we have to be careful in interpreting the results.

Second, this was a study of men who were patients at an infertility clinic. And of the 471 subjects, there were just 26 vegetarians and 5 vegans.

There is no shortage of vegetarians in southern California where the clinic is located. It’s an area that is well-populated by Seventh-day Adventists for one thing. (Loma Linda is an Adventist university.) So why weren’t there more vegetarians coming to the clinic? For all we know, it might be that vegetarians are less likely to seek—or need—treatment for infertility. At any rate, those small numbers make it difficult to interpret the findings.

Another major limitation of the study is that these were self-described vegetarians and vegans. This often gets into fuzzy dietary territory. The scientific literature is packed with studies of “vegetarians” who actually eat some meat.

Finally, while sperm concentrations were lower among the vegetarian groups, they weren’t low enough to matter. That is, the levels were well within the normal range and weren’t low enough to affect fertility(2).

The researchers proposed a couple of different explanations for the differences. They suggested that the vegetarians may have been deficient in vitamin B12. This would be a logical explanation if the men weren’t supplementing, since vitamin B12 levels are correlated with sperm concentrations(3). If that was a problem with this group of vegetarian men, it’s certainly one that is easily rectified. (Have I mentioned before that vegans absolutely need to take vitamin B12 supplements?)

They also proposed that the higher soy content of vegetarian diets might have an effect on sperm concentration. Soyfoods contain isoflavones, which are plant estrogens. But, while that may sound like a bad thing for male fertility, clinical research shows pretty clearly that consuming soy isoflavones has no effect on sperm concentrations in healthy men(4-6).

In fact, one case report found that isoflavone supplements improved sperm concentration in a man seeking treatment for infertility. He went on to father a child after several months of isoflavone treatment(7).

Despite the Loma Linda findings, the bulk of the evidence suggests that soyfoods don’t impact fertility. And there is little reason to think that vegetarianism does either. For one thing, high blood cholesterol levels are linked to poorer sperm and semen parameters, a finding that argues very much in favor of plant-based diets(8). Some types of dairy foods may negatively impact sperm parameters, too(9). And higher intakes of antioxidants–abundant in plant foods, of course–are linked to better sperm concentrations(10).

There is no reason to think that eating a plant-based diet will jeopardize efforts to conceive. (But don’t forget to take your vitamin B12 supplements!)

E.M O, Jacobson JD, Ko EY, Corselli JU, Chan PJ. Decreased sperm concentration and motility in a subpopulation of vegetarian males at a designated blue zone geographic region. Poster presented at: American Society of Reproductive Medicine 70th Annual Meeting; October 22, 2014, Honolulu, Hawaii.

Slama R, Eustache F, Ducot B, et al. Time to pregnancy and semen parameters: a cross-sectional study among fertile couples from four European cities. Hum Reprod 2002;17:503-15.

Boxmeer JC, Smit M, Weber RF, et al. Seminal plasma cobalamin significantly correlates with sperm concentration in men undergoing IVF or ICSI procedures. J Androl 2007;28:521-7.

Mitchell JH, Cawood E, Kinniburgh D, Provan A, Collins AR, Irvine DS. Effect of a phytoestrogen food supplement on reproductive health in normal males. Clin Sci (Lond) 2001;100:613-8.

Beaton LK, McVeigh BL, Dillingham BL, Lampe JW, Duncan AM. Soy protein isolates of varying isoflavone content do not adversely affect semen quality in healthy young men. Fertil Steril 2010;94:1717-22.

Messina M, Watanabe S, Setchell KD. Report on the 8th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment. J Nutr 2009;139:796S-802S.

Casini ML, Gerli S, Unfer V. An infertile couple suffering from oligospermia by partial sperm maturation arrest: can phytoestrogens play a therapeutic role? A case report study. Gynecol Endocrinol 2006;22:399-401. Schisterman EF, Mumford SL, Chen Z, et al. Lipid concentrations and semen quality: the LIFE study. Andrology 2014;2:408-15.