STEP 3B: Do you have high estradiol? Consider the evidence that it can lower testosterone (if you are not on HRT / TRT):
One of the questions I get from time to time is if high estradiol can lower testosterone. The answer is 'yes' of course and below we will provide many lines of evidence from the research that this is the case. However, let's first look at two basic reasons a man can have high estradiol levels in the first place:
Regardless of the reason, there are multiple lines of evidence that high estradiol can significantly lower testosterone and I list those out below:
1. Estradiol-Induced Hypogonadism. Ironically, it is estradiol, not testosterone, that is the primary control mechanism ramping up or down your testosterone production. It is well-known that rising estradiol levels are the way that your body ramps up the feedback loop to turn off testosterone production at the hypothalamus. In a young, healthy male the testes produce an ample supply of testosterone. Have you ever asked yourself what stops testosterone levels from just continually slowly accumulating to unhealthy levels? The answer lies primarily in the estradiol that your body creates from your testosterone via aromatase. As (free) estradiol rises - some sources say it is the free estradiol / free testosterone ratio - it is detected by the hypothalamus and the hypothalaums begins to shut down production. 
This feedback loop is very protective, but it also can backfire with a Western lifestyle. In modern cultures, a high percentage of men are overweight and obese due to over consumption of calories coupled with a sedentary lifestyle. Because fat cells contain aromatase, as men gain weight, their estradiol levels increase. Research shows that if a man is overweight by between 50 and 100 pounds, he can make himself hypogonadal. In other words, his rising estradiol (and plummeting testosterone) actually shut down the hypothalamus almost entirely. I cover just how dramatic this shut down can be in my page on Testosterone and Weight Loss and discuss, for example, one study that showed obese men with average testosterone of 223 ng/dl, which is VERY low testosterone.
Another way we could test this is through steroid users. Men taking steroids inject supraphysiological levels of testosterone (in one form or another), which then are aromatized into massive levels of estradiol. And, sure enough, their testosterone production is shut down and part of any steroid cycle is the PCT (Post Cycle Therapy) that is designed to bring their testosterone production back to life. (It does not always work, however, and they end up on HRT.)
2. Clomid. Some of you may be familiar with Clomid, which many men use to maintain fertility and increase testosterone simultaneously. Clomid works in males by blocking estradiol at the hypothalamus. Again, the fact that Clomid works so well (in men with a functioning HPT axis) shows estradiol's function in testosterone production and how higher estradiol levels can lower testosterone. See my page on Clomid and Testosterone for some additional information.
3. Arimidex Raises Testosterone. If high estradiol really lowers testosterone, then one might expect, or at least hope, that lowering estradiol would raise testosterone. And this is indeed the case. We can actually pharmaceutically lower estradiol with an aromataste inhibitor and see that estradiol climbs higher. The most common aromatase inhibitor (AI) is Arimidex (generic: anastrozole) and, as I show in my link on Testosterone and Arimidex, T levels can be nearly doubled in some men with this strategy. Other AI's have produced similar results.
CAUTION: Using Arimidex to raise testosterone can be risky for several reasons: a) Arimidex interferes to one degree or another with the clotting cascade, b) it is fairly easy to crash your estradiol as some men have a sensitivity and c) thus men with youthful estradiol levels could end up too low (with the potential for osteopenia / osteoporosis).
4. Weight Loss Boosts Testosterone (In Overweight Men). By the same reasoning in #3, one would hope that men who lose significant weight, would increase their total testosterone levels. Again, this is the case and studies that show that dropping 50 or more pounds can double or even triple testosterone levels. Men get many more benefits, of course, including ones that will help them in the bedroom, something I cover in my page on The Many Research-Backed Reasons to Lose Weight.
Also, dieting normally lowers testosterone. However, one study showed that in obese men, weight loss actually resulted in increased testosterone levels. The reasons is that the obese men were so low in testosterone that the weight loss actually reversed the situation.
CONCLUSION: Again, multiple lines of evidence that show that high estradiol levels can lower testosterone levels. There are other reasons that high estradiol is not good for us males as well. Higher estradiol levels have been associated with multiple prostate issues for example. And I believe there is good evidence now that they can actually lead to accelerated atherosclerosis (arterial plaque). See my page on Estadiol and Your Arteries for more information.
What about natural estradiol lowerers? I cover some of the supplemental solutions out there that men use on The Peak Testosterone Forum on this page: Natural Estradiol Decreasers. Men are using Calcium D-Glucarate, zinc, chrysin with piperine and high dose DIM to attempt this. I have cautions about many of these and list them on the above web page. Regardless, these solutions, at least based on what I have seen, do not lower estradiol that much. Therefore, I doubt that a man will get much of a T boost from these. Zinc is the one exception for some men with a deficiency. See my page on Low Testosterone And Zinc Deficiences.
1) Medical Hypotheses, April 1998, 50(4):331-333, "The role of estradiol in the maintenance of secondary hypogonadism in males in erectile dysfunction"][International Journal of Impotence Research, 2003, 15:38 43, "Oestrogen-mediated hormonal imbalance precipitates erectile dysfunction"