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.
Afeiche MC, Bridges ND, Williams PL, et al. Dairy intake and semen quality among men attending a fertility clinic. Fertil Steril 2014;101:1280-7.
10. Zareba P, Colaci DS, Afeiche M, et al. Semen quality in relation to antioxidant intake in a healthy male population. Fertil Steril 2013;100:1572-9.
Thank you for taking the time to investigate this, Ginny!
Thanks for this. You raise some important reservations in interpreting the findings of this recent study.
However, I think you do a disservice to present soy as if we know it’s safe. The literature is equivocal. A more accurate interpretation is that it is not yet clear how phytooestrogens affect human health in general and male reproductive health in particular, but there are reasons to be cautious. Here is just one counter example of a better designed study as a counterpoint to the ones cited in this article regarding male fertility: http://humrep.oxfordjournals.org/content/23/11/2584.abstract
Your piece also states, “while sperm concentrations were lower among the vegetarian groups, they weren’t low enough to matter.” Lowered sperm count would strongly suggest underlying hormonal problems. Just because fertility is still intact doesn’t mean there isn’t a potential problem with broader endocrine disruption. This could apply to women as well as men, and especially to developing children.
There are now countless studies that show harmful effects in animals from soy isoflavones. I’m not saying this means we know soy is bad; I am saying there are abundant reasons to be cautious.
It is too easy to use one piece of research with significant limitations to paint a clear bill of health for soy. A sober look at the literature says it’s not so clear.
Thanks, John. I didn’t mention the Chavarro study because I don’t think it really makes a strong case for harmful effects of soy. For one thing, a lot of the reduced concentration was due to increased ejaculate volume, so actual sperm count wasn’t lower. Also, this study didn’t control for a lot of variables that could affect sperm concentration. And the average soy intake at the high end of intake among these men was 1/2 serving per day. It’s unlikely that isoflavones would be the factor here when intake was so low.
In contrast, the clinical studies which I cited–and which always trump epi data–used much higher isoflavone intakes and didn’t show any effects on sperm concentration and other fertility parameters.
I also place very little value on animal studies. When the human clinical trials are showing something else entirely, then I’m not too worried about what is being shown in animal studies.
A fair assessment of the literature suggests there are likely both benefits and risks to consuming soy. However, non-fermented soy products have been a part of the human diet for an extremely short time. The precautionary principle should be applied. We all want black and white answers about health and diet. Unfortunately, we don’t yet understand the balance of risks and rewards of soy consumption.
Although soy’s impact on human health is not clear, consuming soy clearly benefits the well being of big agriculture. Big ag has spent big money promoting soy. Again, this doesn’t mean soy is bad, but I don’t have much confidence that big ag has the health of the consumer in mind? There is scant historical evidence that it ever has.
If your readers haven’t already, they may be interested in reading Marion Burros’ NY Times piece on this subject. The first portion of the piece is on isoflavone supplementation, so be sure to read to the end, where there is a good discussion of the conclusions (or lack thereof) that can be fairly drawn from current research. The piece is here:
John, there is ample evidence that soy consumption has a very positive effect on women when they begin consuming it in their early teens. There is absolutely NO evidence of soy’s harmful effects, fermented or not. When there IS such evidence I’ll give it up. Until then, I’m not going to forgo an important source of nutrition, soy or any other food that has some hysterics sounding the alarm. Like wheat. Or, a couple centuries ago, tomatoes.
Lowered sperm count is not necessarily a sign of any problems, the underlying assumption here is that the levels seen in people eat meat are normal but they very well may be elevated. For example vegetarians and vegans have, on average, lower cholesterol levels but that isn’t a sign of any problem with vegetarian or vegan diets….rather the opposite. You’d have to show that the lower numbers have some significance before we can start to talk about hormonal problems, etc.
What about zinc? Vegetarian and vegan diets can pretty easily come up short on zinc and low zinc intake can effect sperm quality.
Good point about the zinc. It will be interesting to see if the researchers controlled for this.
Some useless anecdotal evidence for you:
I’m a vegan (of 15 years or so). I eat soy foods on a regular basis. My wife and I tried to have kids twice and we got pregnant on the month we were trying to conceive twice. So 100% success rate. We’re oldish, too, upper 30s, yet we had no problems with fertility.
Would you address the information from the Adventist Health Study that showed women who ate two servings a day of soy had considerably smaller chances of ever bearing a live child? Per jacknorrisrd.com
This is Jack’s analysis of that study: http://jacknorrisrd.com/soy-and-childlessness-2/
I don’t really have anything to add to that. Overall, it’s not a very compelling study.
In this reported study, dairy drinking vegetarians outnumbered vegans 5-1, but the results from both groups are lumped together. The study report I saw does not differentiate the sperm counts of the vegans from the vegetarians. It is possible that the vegetarians had the most dairy intake of all groups and the lowest sperm counts. Therefore, this study might tells us something about the effect of a milk-containing plant-based diet on sperm concentration but it certainly can’t be used to say that a whole foods plant based diet causes low sperm concentrations.
The other issue is that sperm concentration is not a measure of absolute sperm quantity. If the vegetarians have more ejaculate, the sperm concentration may be lower yet the absolute number of sperm may be similar or even higher.
Thanks for this. I was a bit worried cos I’ve been a veg since I was a child (my parents are). But I’m relieved to read all the inconsistencies in the research. Matteo
It’s very easy to blame soy (and all phytoestrogens with it) while discounting one major factor: most of the soy consumed by the participants of pretty much any relevant study, is a GMO, packed with cytotoxins and endocrine disruptors, like glyphosate and polyethoxylated tallowamine, which are perfect fertility killers.
Dan, this doesn’t make any sense. First, many of the clinical studies use isoflavone supplements. How do you know that these are packed with cytotoxins and endocrine disruptors.
And if what you are saying were true, then the research would show that soyfoods are associated with infertility. It doesn’t show this at all.
Ginny, I’m not talking about the specific research quoted in your article, but rather studies that suggest that high consumption of soy and soy-derived products leads to lower fertility rates. One of them was quoted by your readers: http://humrep.oxfordjournals.org/content/23/11/2584.abstract
By the way, isoflavone supplements could easily be contaminated with glyphosate and other toxins, if they are derives from non-organic soy.
what about this study:
I provide to supress eggs and introduce soy (tofu form) in my diet, is a LH /FSH, Free test, total test and oestradiol sufficient to determine if soy is not harmfull for me?
Thanks in advance