Guys are bombarded on the web now with the following formula:
Testosterone = Meat
The corollary to this formula is that vegetarians (and vegans especially) must have lower testosterone levels than their carnivore counterparts. This kind of thinking permeates most popular health blogs and forums out there, especially on Paleo Diet and bodybuilding sites. In addition, almost every major men's health magazine, at least here in the U.S., have recipes and recommendations with meat front and center stage. The message that guys get is clear: if you want to be healthy and hormonal - you must eat meat.
The reasoning behind such thinking is fairly straightforward and goes something like this:
1. Meat is full of saturated fat and the research shows that saturated fat is pro-testosterone.
2. Vegetarian and vegan diets are higher fiber which also has been linked to low testosterone.
3. Bodybuilding, a sport obviously highly dependent on testosterone, is completely dominated by carnivores.
So what do the studies show? Well, first of all, saturated fat is definitely pro-testosterone and it is true that higher fiber diets have some linkage to lower testosterone. I myself have discussed some these issues at length in my links on The Two F's: Fat and Fiber and Testosterone and Diet.
CAUTION: Saturated fat slows down blood flow, something always less than desireable for sexually active males, and can destroys arterial health under most circumstances: read my link on The Potential Dangers of Saturated Fat for more details.
However, what I also bring up, and this is generally ignored by the bodybuilding and Paleo communities, is that vegetarian diets tend to have ample pro-testosterone monounsaturated fats. Even more importantly, vegetarian (and vegan) diets are also high in certain phytochemicals, which have some evidence for increasing testosterone, as I document in my link on Antioxidants and Testosterone. Whole grains, fruits, vegetables, beans, legumes, nuts, seeds are the bulk of what most vegetarians eat and they are all packed with antioxidants, anti-inflammatories and other constituents that will protect and in some cases even stimulate those all-important Leydig cells.
So who is the winner? Well, to date there has only been one study that directly examined this question. The researchers were primarily interested in comparing IGF-1 levels in vegans, vegetarians and meat-eaters, but also monitored a variety of other androgen-related hormones, including testosterone, as well. What they found was that vegetarians and vegans had average testosterone 6% and 16% higher than the carnivores, respectively. This, by the way, was after adjusting for important variables such as age and smoking status.
The one variable that the researchers did not adjust for was BMI (body mass index) and when they did that, the vegetarians and meat-eaters had virtually equal testosterone and vegans were higher than everyone by about 6%. Again, this flies in the face of almost everything you read on the web: supposedly vegans and vegetarians do everything backwards and are loading up on toxic grains, fiber and all the things that will their slam manliness. In fact, though, the truth is that their testosterone levels are perfectly health and may even be higher on average than carnivores. Either way, there is no evidence that vegetarians are suffering from a lack of androgens.
And this really is common sense. Vegetarian diets have been studies extensively and there have been no signs that vegetarians have low testosterone whatsoever. Furthermore, vegetarian (or very close) diets have been adopted by hundreds of millions of people around the globe and there are simply no signs of mass symptoms of low testosterone in these populations. In fact, one could actually argue quite the opposite: cultures and societies that eat low quanitites of meat are known for their active sex lives later in life. (See my book, the Peak Erectile Strength Diet, for other reasons that many plant foods boost erectile strength.)
It should also be noted that those in the study were in early middle age, which means that had lived long enough to accumulate damage to the Leydig cells, the hypothalamus and other key tissues that control and govern testosterone. Therefore, it is possible that younger meat-eating males may have slightly higher testosterone but build up damage from some of the pro-inflammatory or other aspects of a meat-based diet. We just don't know the answer to those kind of questions yet.
One very revealing aspect of the above study was that vegetarians and vegans both had very robust levels of SHBG, again significantly higher than the meat-eaters. SHBG, Sex Hormone-Binding Globulin, is the protein tthat does just what its name implies: it chemically bonds to most of the testosterone in your body. Now that sounds bad, but researchers have noted that generally as SHBG increases so does total testosterone.
The Okinawans are another example that plant-based diets outperform meat-based diets in the long run. The traditional Okinawans were actually not strict vegetarians, as they did eat some pork and fish. However, the great bulk of their diet was always vegetarian and they ate relatively little fat, including saturated fat. Interestingly enough, they also consumed significant soy, which has fairly high levels of various phytoestrogens.
Yet, as I document in my link on How to Avoid Andropause, the average 70-year-old Okinawan has testosterone of 439 ng/dl, a very respectable number, and a direct contrast to the 346 ng/dl average level of the typical 70-year old American.  Just as remarkable is the fact that the typical Okinawan 100-year old has testosterone of 298, which is above the level considered hypogonadal. By any standards, Okinawans have delayed andropause by a couple of decades and are a further sign that the carnivore lifestyle is anything but superior when it comes to preserving and protecting one's testosterone levels..
What about the fact that bodybuilding is dominated by the carnivore lifestyle? Bill Pearl says that after going vegetarian, he had the same amount of muscle that he did when he won his Mr. Universe titles. Kenneth Williams, a vegan bodybuilder, placed third in the 2004 Natural Olympia bodybuilding competition. And, of course, Mike Mahler is long time vegetarian and strength coach extraordinaire. The fact is that, if you desire, one can easily build a massive physique while on a vegetarian or vegan diet.