The Peter Attia Drive - October 17, 2022


#227 - AMA #40： Body composition, protein, time-restricted feeding, fasting, DEXA scans, and more

Topics
DEXA scans interpretation DEXA scans
Hosted by
Peter Attia
Guests
Nick Stenson
#226 ‒ The science of happiness ｜ Arthur Brooks, Ph.D. #228 ‒ Improving body composition, female-specific training principles, and overcoming an eating disorder ｜ Holly Baxter, APD

Episode Stats


Length

15 minutes

Words per minute

178.83

Word count

2,840

Sentence count

174


Summary

Summaries generated with gmurro/bart-large-finetuned-filtered-spotify-podcast-summ .

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

Transcript generated with Whisper (turbo).
Topics generated with Qwen2.5-3B-Instruct.
Hosts, guests, and mentioned names generated with spaCy (en_core_web_sm), reconciled against Wikidata.
00:00:00.000 Hey everyone, welcome to a sneak peek, ask me anything or AMA episode of the drive podcast.
00:00:16.500 I'm your host, Peter Atiyah. At the end of this short episode, I'll explain how you can
00:00:20.460 access the AMA episodes in full, along with a ton of other membership benefits we've created,
00:00:25.440 or you can learn more now by going to peteratiyahmd.com forward slash subscribe.
00:00:31.140 So without further delay, here's today's sneak peek of the ask me anything episode.
00:00:39.260 Welcome to ask me anything episode number 40. I'm once again joined by Nick Stenson. In today's
00:00:45.260 episode, we talk about how to interpret DEXA scans. We've had a lot of questions about this. I've
00:00:50.460 talked about it on and off in various podcasts, both my own and being a guest on a few other
00:00:54.700 podcasts. So we decided to kind of go through this in the exact way that we go through with
00:00:59.960 our patients. So what are the four things that a DEXA scan tells us and how do we interpret each of
00:01:05.880 these things? We then go through, I think about four patient case studies, each of which is
00:01:09.600 illustrative. Again, the likelihood that you will find something of yourself in at least one of these
00:01:15.000 is very high and I think justifies going through all of them. We then kind of talk about protein
00:01:20.420 because one of the things that comes out of interpreting the DEXA scans is how do we assess
00:01:25.240 a person's lean tissue and what we need to do about it. So then kind of answer a whole bunch of
00:01:29.800 questions that came in about protein. How much do you need? When do you need it? How should it be
00:01:34.980 divided throughout the day? We then close the discussion out with a revisit of time-restricted
00:01:40.280 feeding. I've made some comments in the past, I think most recently on the Strong Convictions
00:01:44.440 Loosely Held episode where I talk about my changing views on TRF. And I wouldn't say it's
00:01:51.100 that I'm saying that one should never do TRF, but I have a much more nuanced view of it today than I
00:01:55.680 did five years ago. And I go through both the recent New England Journal of Medicine paper that
00:02:01.200 came out earlier this year that generated a lot of controversy and then add a lot more color to it,
00:02:06.560 including a discussion about circadian rhythm and the relationship of food on the ability to sleep
00:02:12.100 and even some brain health stuff. So if you're a subscriber and want to watch the full video of
00:02:16.820 this podcast, you can find it on the show notes page. And if you're not a subscriber, you can watch
00:02:21.020 a sneak peek of the video on our YouTube page. So without further delay, I hope you enjoy AMA number
00:02:27.620 four. Peter, welcome to another AMA. How are you doing? Doing very well. Excited to talk about this stuff
00:02:38.280 today. Awesome. I don't know if you noticed, but I saw your Instagram post today on Maui Nui Venison.
00:02:44.680 So I wore my Access to Your Institute shirt. I wondered if that was a coincidence, but...
00:02:49.060 The accidental experts. I love that story.
00:02:52.920 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
00:02:58.600 that. Although I'm sure some of what we'll talk about will tie in a little bit to exercise. But what
00:03:04.500 we're going to do is we just kind of gathered a ton of questions all around basically body composition
00:03:09.920 in one way or another. So we're going to start by looking at DEXA scans. This is a topic that
00:03:15.160 has come up a lot in AMAs recently, especially the bone health AMA. And we've gotten a lot of
00:03:20.520 feedback from listeners who they're like, hey, I went and got my DEXA results. I'm trying to understand
00:03:25.860 what they mean. How should I think about them? What matters? What doesn't? So we kind of compiled those
00:03:31.580 and we're going to do a deeper dive into that, including looking at some real life patient
00:03:36.080 case studies. So what we had is the team pulled specific patients that you have. And we thought
00:03:42.240 were kind of good overarching studies that kind of show people how they can think about this. And
00:03:48.520 then also what changes need to be made based on those results. So kind of not only how to understand
00:03:54.060 the DEXA, but then how you apply that to your life. And then from there, we're going to do some
00:03:58.980 follow-up questions that mainly came from the Strong Convictions Loosely Held podcast and really
00:04:04.120 around your comments on protein consumption and really how you get as much protein in throughout the
00:04:10.680 day as you want to. And then also some follow-up questions on your comments regarding your views on
00:04:17.400 time-restricted feeding. So if it all goes to according to plan, we'll wrap all that. But I think
00:04:22.380 it will all kind of fit together because I think a lot of what we'll talk about in the protein,
00:04:26.300 time-restricted feeding will play off what we learn in the DEXA. So with that said, anything
00:04:32.300 you want to add before we kind of jump into the first question? Nope, let's go for it.
00:04:37.500 Perfect. So the first one, keep it simple, just how should people interpret their DEXA scans? So
00:04:44.760 when your patients do them and you do them and you look at the results, what do you care about? What
00:04:50.340 are you looking at? And even what metrics are they providing that you don't care about?
00:04:55.000 Probably first I should explain what a DEXA scan is for folks. So a DEXA scan is an X-ray. Basically,
00:05:01.420 it's a sort of a moving X-ray. So you lay on a table and a really, really low powered X-ray,
00:05:08.860 so meaning very little ionizing radiation is sort of run across your body. And the way all X-rays work
00:05:15.640 basically is there's a plate behind the object or the person being X-rayed. And it's effectively
00:05:23.460 looking at what's hitting the plate. And the more dense something is in front of the plate,
00:05:28.940 the less electrons that are going to hit the back of the plate. Now there's a unit in radiation that
00:05:36.320 we talk about, and it's usually millisieverts. We talk about how many millisieverts of radiation
00:05:42.680 something offers you. And more radiation to some extent is harmful. And so the NRC recommends that
00:05:51.020 a person receive no more of 50 millisieverts in a year, in a calendar year. So the question is then
00:05:58.540 how do you put that in context, right? So just living at sea level is something to the tune of one
00:06:04.400 to two millisieverts per year. So just being exposed to the sun at sea level, not just the sun,
00:06:13.020 but of course everything that's ionizing in space, basically it exposes you to two, three,
00:06:18.720 maybe 4% of your annual allotment. And that changes. So if you lived in Colorado,
00:06:24.000 you know, where you're basically a mile above sea level, it's about twice that amount that you're
00:06:27.220 getting. But when you start to look at something like a flight, like what is an East Coast to West
00:06:31.720 Coast flight? Well, you know, it's a certain amount of radiation. It's not nearly as much as
00:06:36.160 if you're going over the poles, but now you have to measure those things in microsieverts. That's
00:06:40.400 how much lower it is. So a flight would be like 40 microsieverts. And again, a microsievert is one
00:06:46.040 one thousandth of a millisievert. What about a mammogram? So a mammogram would be about 400
00:06:51.720 microsieverts or 0.4 millisieverts. Chest X-ray, depending on the size of the individual,
00:06:58.660 maybe 25 to 50 microsieverts. Conversely, a CT scan of the chest, abdomen, and pelvis could be up to 20
00:07:07.540 millisieverts, which would be about 40% of your annual allotment. So why am I saying all this?
00:07:12.480 Well, I just want to put DEXA in context because it is a virtually radiation-free technology. It is
00:07:18.840 insanely low. I won't get into all the details of why, but it's typically less than 20 microsieverts.
00:07:25.980 That's sort of the punchline. So a DEXA has no more radiation than even the lowest end of a chest
00:07:32.780 X-ray. And we're talking about, gosh, like one twentieth of the radiation of a mammogram
00:07:39.100 and about half the radiation of a cross-country flight. All of that is to say DEXA is a really
00:07:45.080 safe, low risk. There's effectively zero risk to a DEXA scan. And it's not something you need to do
00:07:51.460 that often. We have some patients when they come into the practice, they're ordering DEXA scans,
00:07:54.620 or they've been doing DEXA scans on themselves every six weeks. That's a total waste of time.
00:07:58.600 This is a type of scan that you would do once, maybe twice per year. It has the capacity to
00:08:03.580 distinguish effectively three things, bone, fat, and other. Those are basically the three buckets
00:08:11.820 that DEXA is distinguishing based on the density of what the electrons are going through.
00:08:17.580 So when you do the scan, you basically get four pieces of information if you're looking closely
00:08:25.000 at it. Now, again, when most people go and get a DEXA scan, they're kind of looking at one thing,
00:08:28.240 which is what's my body fat. And again, body fat can be calculated in two ways, but probably the
00:08:33.080 best way to do it is to take the total amount of fat and divide it by the total mass of the
00:08:38.760 individual. And that gives you percent body fat. Technically, you can subtract out bone mass when
00:08:44.000 you do that and get tissue fat percent. But, and by the way, that doesn't differ very much because
00:08:48.200 bones don't weigh that much. Just in case you're wondering where that discrepancy can be. So
00:08:52.640 certainly body fat is a relevant consideration. We'll talk about it. But I think there's three
00:08:57.300 others that are more important. And the first is actually BMD, bone mineral density. That is both
00:09:03.100 reported in an absolute amount in grams per centimeter squared. And it's also reported in a Z score.
00:09:10.340 Now, I think we probably covered a lot of this in the previous AMA on bone health. So I won't go
00:09:14.660 into any more detail on that. The next thing that you get is an estimate of VAT or visceral adipose
00:09:21.560 tissue. Again, I won't go into how this is done, but it is clearly just an estimate. And it's based on
00:09:28.780 looking at the amount of fat that is in the torso above the anterior superior iliac crest and the ribs
00:09:39.760 and kind of trying to subtract out what it believes is in the subcutaneous space and therefore looking
00:09:47.040 at the difference. And as you'll see, visceral fat is a relatively small fraction of total body fat,
00:09:52.600 but it's important to get that right because it's so much more indicative of risk.
00:09:58.120 And the final thing that it gives you is sometimes it does this directly. It just tells you the
00:10:03.700 appendicular lean mass index. And sometimes you just have to calculate it. And you can always calculate
00:10:07.480 the fat free mass index with both of which we'll talk about. So these are measures of how much lean
00:10:13.200 mass you have or muscle mass in the extremities. And the way this is always reported is total amount
00:10:19.920 of lean tissue divided by height in meters squared. So both appendicular lean mass index and fat free mass
00:10:27.260 index, which is just total mass that is not fat divided by height in meters squared. They're both
00:10:34.360 reported therefore in kilograms per meter squared. So those are the four things you get when you do
00:10:39.520 a DEXA. And of course, all of these things, you want to see how you stack up against a population.
00:10:46.620 And that population is typically stratified by your sex and by your age. So therefore, we have
00:10:53.500 nomograms for each of these things. And that's how we present the data to a patient. And that's how we
00:10:57.820 therefore make decisions about where you rank and what you need to do.
00:11:00.940 So to clarify on that, so the bone mineral density, the VAT, ALMI, and FFMI, those are the four major
00:11:09.500 things. And now I think I've heard you say before is not every place you get a DEXA scan will give you
00:11:16.080 those metrics, but every place will provide the metrics you need to come to the conclusion of that
00:11:22.320 for yourself. With one exception. So there are some DEXA places that only give total body Z score for
00:11:33.140 bone, and they don't break it out individually by hip and lumbar spine. This is important because,
00:11:40.920 again, I believe I spoke about this on the previous AMA, you can't make a diagnosis of osteopenia
00:11:46.260 or osteoporosis or frankly assess BMD clinically without that feature. In other words, if you just
00:11:54.240 look at total body BMD, the Z score for the total body is too easy to mask what's going on in those
00:12:01.100 areas. So it doesn't mean you can't get a DEXA at one of those places. You can, but you just have to
00:12:05.680 understand there's a blind spot, which is you're not getting adequate information about BMD. So if
00:12:10.860 there's any concern about BMD, you're going to have to go to a place that is able to give the
00:12:16.020 segmented information. Which is good for people to know just because as they're Googling different
00:12:21.500 places and calling around, it gives them something specific to ask for to get a good understanding.
00:12:25.920 Yeah. So on that, I think what makes sense to do next is dive into each of those four metrics a
00:12:32.020 little more and kind of what they mean and why they're important. With BMD, as you mentioned,
00:12:37.100 we covered that in a BMD AMA, which was AMA 37 for anyone who hasn't listened to it and wants to go
00:12:43.720 back and listen. I don't think we really need to dive into that in as much detail just based on that
00:12:49.580 AMA, but the VAT, ALMI, and FFMI, I think might be worth getting into because I think those are metrics
00:12:56.740 that most people aren't hearing about where body fat percentage, I think everyone is aware of that.
00:13:02.660 They conceptually know what that is, but the other three, I think for people not in the space,
00:13:07.720 it's a little outside of their understanding.
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