Friday, November 14, 2014

Do vegetarians or vegans "have much lower sperm counts" than omnivores?

Vegetarians have much lower sperm counts - Telegraph

This study doesn't support claims that "vegetarians (in general) have much lower sperm counts" than omnivores, and doesn't provide any evidence that avoiding consumption of animals makes men infertile.  Here's why that headline is bunk:

1.  The study being reported has not been peer-reviewed nor is it published but was only a poster presentation at a conference.

2.  All subjects in this study were patients at a clinic for infertility.  This study says nothing about the sperm counts of vegetarians who are not infertility patients, nor about incidence of infertility among vegans relative to the incidence among omnivores in the general population.  If you think it does, you need to brush up on the fallacy of composition.

However, I think it is worth noting that at this infertility clinic, the omnivores who came for evaluation outnumbered the vegans 20-to-1. The idea that infertility is a uniquely vegetarian or vegan problem is absurd.

Further, the idea that a diet low in animal products causes infertility conflicts with the fact that birth rates are and have been for hundreds of years higher in nations where the typical diet is low in animal products.  As I discussed extensively in Powered By Plants, there in fat exists a clear inverse and dose-response relationship between national fertility rates and animal protein intake: nations with the highest animal protein intake have the lowest fertility rates, nations with the lowest animal protein intake have the highest fertility rates. 

Source:  Powered By Plants

If avoiding animal products causes human infertility, then India (and Asia in general) should have lower populations than European nations.  Based on the evidence in this table plus experimental evidence that found reduced fertility in animals fed animal protein, Roger Williams, the man who discovered pantothenic acid and named folic acid, suggested in 1971 that increasing animal protein intake would be an effective anti-fertility measure for reducing world population.[1]

3. This study involved more than 400 omnivores but only 31 vegetarians and vegans. Since they compared average sperm concentrations, the averages of the vegetarian/vegan group would have been more profoundly affected by a few people having very low levels while the omnivore group had more total people to dilute any outliers.  This is bad science.

4. The vegetarian/vegan group included men who ate dairy (vegetarians).  In fact, the dairy drinking vegetarians outnumbered vegans 5-to-1.  The study reports I have seen do not differentiate the sperm concentrations of the vegans from the vegetarians.  It is possible that the vegetarians had the most dairy intake of all groups and the lowest sperm concentrations.  Therefore, this study probably tells us more about the effect of a milk-containing plant-based diet on sperm concentrations than the effect of a plant-based diet.

5.  Nevertheless, the average sperm concentration of the vegetarian/vegan group was in the normal range.  This brings up the whole "normal range" idea.  The "normal range" is just what is normal, not what is optimal.  People eating plant-based diets tend to have a lot of measures on the low side of the "normal range" including low cholesterol, low LDL, low BMI, low blood glucose, etc.  Just because a number is lower doesn't mean it is pathological; and more ≠ better.

6.  The sperm concentration is given as sperm number per milliliter semen. No mention was made of total milliters of semen in either group.  If the vegetarians/vegans had on average greater total semen production, they may have had similar absolute numbers of sperm despite lower concentration.  Percentages are not absolute numbers.  This is basic math. 

Nor does lower sperm concentration equal low fertility.  Ejaculate volume plays an important role in fertility, and the greater the ejaculate volume, the more likely there will be a lower sperm concentration.

Imagine you want to get some goldfish to visit every corner of a 5 gallon aquarium.  You try two different methods.  In the first, you put 10 goldfish in 1 gallon of water – a concentration of 10 goldish per gallon, then inject the water into the 5 gallon aquarium.  You find that the goldfish are unable to reach the upper part of the aquarium.  Although the fish are in a high concentration, the medium they use for transportation is limited, preventing them from reaching every corner of the aquarium.

Next you put 20 goldfish in 5 gallons of water.  The concentration is now only 4 goldfish per gallon, less than half of the concentration used in the first experiment.  However, now the water fills the aquarium and the fish are easily able to reach every corner of the vessel. 

This thought experiment should make it clear that a high sperm concentration in a low volume of ejaculate may actually make a man less fertile that a lower sperm concentration in a larger volume of ejaculate. 

Therefore, the idea that men with low sperm concentrations are ipso facto less fertile than those with high concentrations does not float. 

7.  There is no one vegan or vegetarian diet.  This study report says that the authors suggested a link between low sperm counts and low B12.  B12 is not an animal product, it is a microbial product.  

In addition, many vegetarians and vegans eat inadequate diets rich in junk foods, as do many omnivores.  Those who do are more likely to be consulting a fertility clinic than those who do not.  Taking the sperm quality of milk-using vegetarians who have elected to go to a fertility clinic as somehow indicative of the sperm quality of all milk-using vegetarian males is like taking the average income of Hispanic men who consulted the unemployment office as somehow indicative of the average income of the average Hispanic male.  This is called the fallacy of composition.  

The average sperm quality of a group consisting primarily of dairy-consuming vegetarian patients at a fertility clinic simply does not tell us anything about of the sperm quality of vegan men who don't consult a fertility clinic.  Anyone who claims that this report shows that a vegan diet makes men infertile or have low sperm concentrations simply has no logical or empirical foundation to stand upon.

You can't paint all plant-based diets with one brush. These could have been a particularly poorly nourished group of dairy-dependent vegetarians.

In short, this widely disseminated report doesn't tell us anything about the relative fertility of either vegetarians or vegans in comparison to omnivores.  It is just bad science. 


Fred Pollack said...

I agree with Don. Dr. Greger has 2 short videos (about 1 month ago) that nailed this subject:
Click on "sources cited" to the right of each video to get links to the medical literature referenced in the videos.

Toflin Swedol said...

Wat een lovenswaardig werk dat je hebt gedaan, met simpelste taal. Ik kan mezelf niet weerstaan om een reactie achter te laten en geloof me het is moeilijk te imponeren mij.
Maar De Maaltijden volgens Het Paleo Dieet Bestaan uit vlees, vis, groente, fruit, noten en zaden.