#227 - AMA #40： Body composition, protein, time-restricted feeding, fasting, DEXA scans, and more
Episode Stats
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Summary
In this episode, Dr. Nick Stenson and I discuss how to interpret data from a DEXA scan, protein consumption, and time restricted feeding (TRF) as it pertains to body composition and overall health.
Transcript
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Hey everyone, welcome to a sneak peek, ask me anything or AMA episode of the drive podcast.
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I'm your host, Peter Atiyah. At the end of this short episode, I'll explain how you can
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So without further delay, here's today's sneak peek of the ask me anything episode.
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Welcome to ask me anything episode number 40. I'm once again joined by Nick Stenson. In today's
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episode, we talk about how to interpret DEXA scans. We've had a lot of questions about this. I've
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talked about it on and off in various podcasts, both my own and being a guest on a few other
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podcasts. So we decided to kind of go through this in the exact way that we go through with
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our patients. So what are the four things that a DEXA scan tells us and how do we interpret each of
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these things? We then go through, I think about four patient case studies, each of which is
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illustrative. Again, the likelihood that you will find something of yourself in at least one of these
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is very high and I think justifies going through all of them. We then kind of talk about protein
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because one of the things that comes out of interpreting the DEXA scans is how do we assess
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a person's lean tissue and what we need to do about it. So then kind of answer a whole bunch of
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questions that came in about protein. How much do you need? When do you need it? How should it be
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divided throughout the day? We then close the discussion out with a revisit of time-restricted
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feeding. I've made some comments in the past, I think most recently on the Strong Convictions
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Loosely Held episode where I talk about my changing views on TRF. And I wouldn't say it's
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that I'm saying that one should never do TRF, but I have a much more nuanced view of it today than I
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did five years ago. And I go through both the recent New England Journal of Medicine paper that
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came out earlier this year that generated a lot of controversy and then add a lot more color to it,
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including a discussion about circadian rhythm and the relationship of food on the ability to sleep
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and even some brain health stuff. So if you're a subscriber and want to watch the full video of
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this podcast, you can find it on the show notes page. And if you're not a subscriber, you can watch
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a sneak peek of the video on our YouTube page. So without further delay, I hope you enjoy AMA number
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four. Peter, welcome to another AMA. How are you doing? Doing very well. Excited to talk about this stuff
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today. Awesome. I don't know if you noticed, but I saw your Instagram post today on Maui Nui Venison.
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So I wore my Access to Your Institute shirt. I wondered if that was a coincidence, but...
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So for today's AMA, it's not going to be on exercise like the past to have been. We're going to stick to
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that. Although I'm sure some of what we'll talk about will tie in a little bit to exercise. But what
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we're going to do is we just kind of gathered a ton of questions all around basically body composition
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in one way or another. So we're going to start by looking at DEXA scans. This is a topic that
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has come up a lot in AMAs recently, especially the bone health AMA. And we've gotten a lot of
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feedback from listeners who they're like, hey, I went and got my DEXA results. I'm trying to understand
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what they mean. How should I think about them? What matters? What doesn't? So we kind of compiled those
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and we're going to do a deeper dive into that, including looking at some real life patient
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case studies. So what we had is the team pulled specific patients that you have. And we thought
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were kind of good overarching studies that kind of show people how they can think about this. And
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then also what changes need to be made based on those results. So kind of not only how to understand
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the DEXA, but then how you apply that to your life. And then from there, we're going to do some
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follow-up questions that mainly came from the Strong Convictions Loosely Held podcast and really
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around your comments on protein consumption and really how you get as much protein in throughout the
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day as you want to. And then also some follow-up questions on your comments regarding your views on
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time-restricted feeding. So if it all goes to according to plan, we'll wrap all that. But I think
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it will all kind of fit together because I think a lot of what we'll talk about in the protein,
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time-restricted feeding will play off what we learn in the DEXA. So with that said, anything
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you want to add before we kind of jump into the first question? Nope, let's go for it.
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Perfect. So the first one, keep it simple, just how should people interpret their DEXA scans? So
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when your patients do them and you do them and you look at the results, what do you care about? What
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are you looking at? And even what metrics are they providing that you don't care about?
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Probably first I should explain what a DEXA scan is for folks. So a DEXA scan is an X-ray. Basically,
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it's a sort of a moving X-ray. So you lay on a table and a really, really low powered X-ray,
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so meaning very little ionizing radiation is sort of run across your body. And the way all X-rays work
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basically is there's a plate behind the object or the person being X-rayed. And it's effectively
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looking at what's hitting the plate. And the more dense something is in front of the plate,
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the less electrons that are going to hit the back of the plate. Now there's a unit in radiation that
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we talk about, and it's usually millisieverts. We talk about how many millisieverts of radiation
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something offers you. And more radiation to some extent is harmful. And so the NRC recommends that
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a person receive no more of 50 millisieverts in a year, in a calendar year. So the question is then
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how do you put that in context, right? So just living at sea level is something to the tune of one
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to two millisieverts per year. So just being exposed to the sun at sea level, not just the sun,
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but of course everything that's ionizing in space, basically it exposes you to two, three,
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maybe 4% of your annual allotment. And that changes. So if you lived in Colorado,
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you know, where you're basically a mile above sea level, it's about twice that amount that you're
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getting. But when you start to look at something like a flight, like what is an East Coast to West
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Coast flight? Well, you know, it's a certain amount of radiation. It's not nearly as much as
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if you're going over the poles, but now you have to measure those things in microsieverts. That's
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how much lower it is. So a flight would be like 40 microsieverts. And again, a microsievert is one
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one thousandth of a millisievert. What about a mammogram? So a mammogram would be about 400
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microsieverts or 0.4 millisieverts. Chest X-ray, depending on the size of the individual,
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maybe 25 to 50 microsieverts. Conversely, a CT scan of the chest, abdomen, and pelvis could be up to 20
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millisieverts, which would be about 40% of your annual allotment. So why am I saying all this?
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Well, I just want to put DEXA in context because it is a virtually radiation-free technology. It is
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insanely low. I won't get into all the details of why, but it's typically less than 20 microsieverts.
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That's sort of the punchline. So a DEXA has no more radiation than even the lowest end of a chest
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X-ray. And we're talking about, gosh, like one twentieth of the radiation of a mammogram
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and about half the radiation of a cross-country flight. All of that is to say DEXA is a really
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safe, low risk. There's effectively zero risk to a DEXA scan. And it's not something you need to do
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that often. We have some patients when they come into the practice, they're ordering DEXA scans,
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or they've been doing DEXA scans on themselves every six weeks. That's a total waste of time.
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This is a type of scan that you would do once, maybe twice per year. It has the capacity to
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distinguish effectively three things, bone, fat, and other. Those are basically the three buckets
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that DEXA is distinguishing based on the density of what the electrons are going through.
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So when you do the scan, you basically get four pieces of information if you're looking closely
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at it. Now, again, when most people go and get a DEXA scan, they're kind of looking at one thing,
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which is what's my body fat. And again, body fat can be calculated in two ways, but probably the
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best way to do it is to take the total amount of fat and divide it by the total mass of the
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individual. And that gives you percent body fat. Technically, you can subtract out bone mass when
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you do that and get tissue fat percent. But, and by the way, that doesn't differ very much because
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bones don't weigh that much. Just in case you're wondering where that discrepancy can be. So
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certainly body fat is a relevant consideration. We'll talk about it. But I think there's three
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others that are more important. And the first is actually BMD, bone mineral density. That is both
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reported in an absolute amount in grams per centimeter squared. And it's also reported in a Z score.
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Now, I think we probably covered a lot of this in the previous AMA on bone health. So I won't go
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into any more detail on that. The next thing that you get is an estimate of VAT or visceral adipose
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tissue. Again, I won't go into how this is done, but it is clearly just an estimate. And it's based on
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looking at the amount of fat that is in the torso above the anterior superior iliac crest and the ribs
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and kind of trying to subtract out what it believes is in the subcutaneous space and therefore looking
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at the difference. And as you'll see, visceral fat is a relatively small fraction of total body fat,
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but it's important to get that right because it's so much more indicative of risk.
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And the final thing that it gives you is sometimes it does this directly. It just tells you the
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appendicular lean mass index. And sometimes you just have to calculate it. And you can always calculate
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the fat free mass index with both of which we'll talk about. So these are measures of how much lean
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mass you have or muscle mass in the extremities. And the way this is always reported is total amount
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of lean tissue divided by height in meters squared. So both appendicular lean mass index and fat free mass
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index, which is just total mass that is not fat divided by height in meters squared. They're both
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reported therefore in kilograms per meter squared. So those are the four things you get when you do
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a DEXA. And of course, all of these things, you want to see how you stack up against a population.
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And that population is typically stratified by your sex and by your age. So therefore, we have
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nomograms for each of these things. And that's how we present the data to a patient. And that's how we
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therefore make decisions about where you rank and what you need to do.
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So to clarify on that, so the bone mineral density, the VAT, ALMI, and FFMI, those are the four major
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things. And now I think I've heard you say before is not every place you get a DEXA scan will give you
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those metrics, but every place will provide the metrics you need to come to the conclusion of that
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for yourself. With one exception. So there are some DEXA places that only give total body Z score for
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bone, and they don't break it out individually by hip and lumbar spine. This is important because,
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again, I believe I spoke about this on the previous AMA, you can't make a diagnosis of osteopenia
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or osteoporosis or frankly assess BMD clinically without that feature. In other words, if you just
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look at total body BMD, the Z score for the total body is too easy to mask what's going on in those
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areas. So it doesn't mean you can't get a DEXA at one of those places. You can, but you just have to
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understand there's a blind spot, which is you're not getting adequate information about BMD. So if
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there's any concern about BMD, you're going to have to go to a place that is able to give the
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segmented information. Which is good for people to know just because as they're Googling different
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places and calling around, it gives them something specific to ask for to get a good understanding.
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Yeah. So on that, I think what makes sense to do next is dive into each of those four metrics a
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little more and kind of what they mean and why they're important. With BMD, as you mentioned,
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we covered that in a BMD AMA, which was AMA 37 for anyone who hasn't listened to it and wants to go
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back and listen. I don't think we really need to dive into that in as much detail just based on that
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AMA, but the VAT, ALMI, and FFMI, I think might be worth getting into because I think those are metrics
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that most people aren't hearing about where body fat percentage, I think everyone is aware of that.
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They conceptually know what that is, but the other three, I think for people not in the space,
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