AMA #10: Low testosterone, hypothyroidism, building muscle (and preserving it while fasting)

**Peter Attia** (0:04)
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The Drive is a result of my hunger for optimizing performance, health, longevity, critical thinking, along with a few other obsessions along the way. I've spent the last several years working with some of the most successful top-performing individuals in the world. And this podcast is my attempt to synthesize what I've learned along the way to help you live a higher quality, more fulfilling life. If you enjoy this podcast, you can find more information on today's episode and other topics at peterattiamd.com.
Welcome to another edition of Ask Me Anything. Once again, I'm joined by my head of research and my sidekick, Bob Kaplan.
In this episode, we go really deep on about three things. There's no speed round, but I think we make up for it by just the depth rather than the breadth. So the first thing we talk about is testosterone replacement for men specifically, when it's appropriate, related risks, benefits, the laboratory values one should and shouldn't care about. So apologies that this one is a little more gender specific, but I think we've also already covered this on the female side. So this is a very male-centric view of testosterone replacement therapy. Second thing we jump into is thyroid replacement therapy, and just in general, thyroid hormones, how they're produced, how the diagnosis of hypothyroidism is made, in my opinion, how that differs from maybe the standard way that people think about it and all sorts of other tangential things around that. And then lastly, we talk about exercise, and specifically we talk about exercise and how it relates to nutrition with respect to building muscle. Now, to be completely clear, and I disclose this fully in the episode, I don't consider myself an expert on muscle building, body building, anything like that. You certainly wouldn't want me as your coach if you were training for such things. But at the general population level, which is where I consider myself to be, I think I hopefully know enough to add value here. So anyway, we talk a lot about the role of fasting, caloric restriction up and down, and muscle accumulation versus loss of muscle. We also talk about autophagy, IGF, or insulin-like growth factor, and mTOR in the process. So without further delay, here is AMA number 10 As a reminder, AMAs are for subscribers only. If you're not a subscriber, you'll only be able to hear a preview of the AMA here.
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**Bob Kaplan** (2:41)
Hello, podcasters. Welcome to another Ask Me Anything. I am joined by Peter Attia. This is Bob Kaplan.
Peter, how are you doing?

**Peter Attia** (2:51)
I'm doing good, Bob. How are you?

**Bob Kaplan** (2:52)
Doing well.
Thought we'd just jump right into it. Start off with some testosterone.

**Peter Attia** (2:59)
Wow, no foreplay. Go for it.

**Bob Kaplan** (3:01)
Yeah, a lot of questions around testosterone. The essential question is, are you a fan of testosterone supplementation as men age?
If so, to what targets?

**Peter Attia** (3:14)
Well, I mean, this is sort of a tough question. It's very difficult to answer these questions in isolation because they're kind of dependent on individual patients. Bear with me, I suppose, as I kind of give a soliloquy.
Regardless of what you're talking about manipulating in medicine, you should ask yourself the question, what is the desired outcome? Am I manipulating this variable because I believe it improves longevity? If so, does it improve lifespan? Does it improve healthspan? Both? Neither? One more than the other? Testosterone, let's just now evaluate testosterone replacement through that lens, which is what do we believe it can help with? Well, I'm not really particularly convinced that normalization of testosterone will improve lifespan. I could be wrong on this. There are certainly associations that would suggest that that could be the case. For example, low testosterone is not only associated with prostate cancer, but is associated with more aggressive prostate cancer. By the way, I think that that's probably not saying that low testosterone causes aggressive prostate cancer. I think it says that if you have prostate cancer in a low androgen environment, it is likely to be more aggressive.
We could probably spend an entire AMA just debating the merits of testosterone replacement therapy, but in spending a lot of time in this literature, I don't see a clear and obvious case that one will live longer because of it. And again, living longer by definition means delay the onset of death, at least as it pertains to chronic disease.