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

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Welcome to Ask Me Anything episode number 40. I'm once again joined by Nick Stenson. In today's episode we talk about how to interpret DEXA scans. We've had a lot of questions about this. I've talked about it on and off in various podcasts, both my own and being a guest on a few other podcasts. So we decided to kind of go through this in the exact way that we go through with our patients. So what are the four things that a DEXA scan tells us and how do we interpret each of these things? We then go through, I think about four patient case studies, each of which is illustrative. Again, the likelihood that you will find something of yourself in at least one of these is very high and I think justifies going through all of them. We then kind of talk about protein because one of the things that comes out of interpreting the DEXA scans is how do we assess a person's lean tissue and what we need to do about it. So then kind of answer a whole bunch of questions that came in about protein. How much do you need? When do you need it? How should it be divided throughout the day. We then close the discussion out with a revisit of time restricted feeding. I've made some comments in the past, I think most recently on the Strong Convictions Loosely Held episode where I talk about my changing views on trf. And I wouldn't say it's that I'm saying that one should never do trf. But I have a much more nuanced view of it today than I did five years ago. And I go through both the recent New England Journal of Medicine paper that came out earlier this year that generated a lot of controversy and then add a lot more color to it, including a discussion about circadian rhythm and the relationship of food, on the ability to sleep, and even some brain health stuff. So if you're a subscriber and want to watch the full video of this podcast, you can find it on the Show Notes page. And if you're not a subscriber, you can watch a sneak peek of the video on our YouTube page. So without further delay, I hope you.

Enjoy AMA number 40.

Peter, welcome to another ama. How you doing?

Doing very well. Excited to talk about this stuff today.

Awesome. I don't know if you noticed, but I saw your Instagram post today on Maui Nui venison, so I wore my Access Deer Institute shirt.

I wondered if that was a coincidence.

But the accidental experts, I love that story. 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 that. Although I'm sure some of what we'll talk about will tie in a little bit to exercise. But what we're going to do is we just kind of gathered a ton of questions all around, basically body composition in one way or another. So we're going to start by looking at DEXA scans. That this is a topic that has come up a lot in AMAs recently, especially the bone health AMA. And we've gotten a lot of feedback from listeners who they're like, hey, I went and got my DEXA results. I'm trying to understand what they mean, how should I think about them, what matters, what doesn't. So we kind of compiled those and we're going to do a deeper dive into that, including looking at some real life patient case studies. So what we had is the team pulled specific patients that you have and we thought were kind of good overarching studies that kind of show people how they can think about this and then also what changes need to be made based on those results. So kind of not only how to understand the DEXA, but then how you apply that to your life. And then from there we're going to do some follow up questions that mainly came from the Strong Convictions Loosely Held podcast and really around your comments on protein consumption and really how you get as much protein in throughout the day as you want to. And then also some follow up questions on your comments regarding your views on time restricted feeding. So if it all goes to according to plan, we'll wrap all that. But I think it will all kind of fit together because I think a lot of what we'll talk about in the protein time restricted feeding will play off what we learn in the dexa. So with that said, anything you want to add before we kind of jump into the first question?

Nope. Let's go for it.

Perfect. So the first one, keep it simple. Just how should people interpret their DEXA scans? So when your patients do them and you do them and you look at the results what do you care about? What are you looking at? And even what metrics are they providing that you don't care about?

Probably first I should explain what a DEXA scan is for, folks. So a DEXA scan is an X ray, basically. It's sort of a moving X ray, so you lay on a table and a really, really low powered X ray, so meaning very little ionizing radiation is sort of run across your body. And the way all X rays work basically is there's a plate behind the object or the person being X rayed, and it's effectively looking at what's hitting the plate. And the more dense something is in front of the plate, the less electrons that are going to hit the plate, the back of the plate. Now, there's a unit in radiation that we talk about, and it's usually millisieverts. We talk about how many millisieverts of radiation something offers you. And more radiation to some extent is harmful. And so the NRC recommends that a person receive no more of 50 millisieverts in a year, in a calendar year. So the question is then, how do you put that in context? Right, so just living at sea level is something to the tune of 1-2-millisieverts per year. So just being exposed to the sun at sea level, not just the sun, but of course, everything that's ionizing in space basically exposes you to 2, 3, maybe 4% of your annual allotment. And that changes. So if you lived in Colorado, you know, where you're basically a mile above sea level, it's about twice that amount that you're getting. But when you start to look at something like a flight, like what is an east coast to west coast flight? Well, you know, it's a certain amount of radiation. It's not nearly as much as if you're going over the poles. But now you have to measure those things in micro sieverts. That's how much lower it is. So a flight would be like 40 micro sieverts. And again, a micro sievert is 1 1000th of a millisievert. What about a mammogram? So a mammogram would be about 400 microsieverts or 0.4 millisieverts. Chest X ray, depending on the size of the individual, maybe 25 to 50 microsieverts. Conversely, a CT scan of the chest, abdomen and pelvis could be up to 20 millisieverts, which would be about 40% of your annual allotment. So why am I saying all this Well, I just want to put DEXA in context because it is a virtually radiation free technology. It is insanely low. I won't get into all the details of why, but it's typically less than 20 micro sieverts. That's sort of the punchline. So a DEXA has no more radiation than even the lowest end of a chest X ray. And we're talking about, gosh, like 1/20 of the radiation of a mammogram and about half the radiation of a cross country flight. All of that is to say DEXA is a really safe, low risk. There's effectively zero risk to a DEXA scan and it's not something you need to do that often. We have some patients, when they come into the practice, they're ordering DEXA scans, or they've been doing DEXA scans on themselves every six weeks. That's a total waste of time. This is a type of scan that you would do once, maybe twice per year. It has the capacity to distinguish effectively three things, bone, fat and other. Those are basically the three buckets that DEXA is distinguishing based on the density of what the electrons are going through. So when you do the scan, you basically get four pieces of information if you're looking closely at it. Now, again, when most people go and get a DEXA scan, they're kind of looking at one thing, which is what's my body fat? And again, body fat can be calculated in two ways. But probably the best way to do it is to take the total amount of fat and divide it by the total mass of the individual. And that gives you percent body fat. Technically you can subtract out bone mass when you do that and get tissue fat percent. But, and by the way, that doesn't differ very much because bones don't weigh that much, just in case you're wondering where that discrepancy can be. So certainly body fat is a relevant consideration. We'll talk about it. But I think there's three others that are more important. And the first is actually bmd bone mineral density that is both reported in an absolute amount in grams per centimeter squared, and it's also reported in a Z score. Now, I think we probably covered a lot of this in the previous AMA on bone health, so I won't go into any more detail on that. The next thing that you get is an estimate of VAT or visceral adipose tissue. Again, I won't go into how this is done, but it is clearly just an estimate and it's based on looking at the Amount of fat that is in the torso above the anterior superior iliac crest and the ribs, and kind of trying to subtract out what it believes is in the subcutaneous space. And therefore looking at the difference, and as you'll see, visceral fat is a relatively small fraction of total body fat. But it's important to get that right because it's so much more indicative of risk. And the final thing that it gives you is sometimes it does this directly, it just tells you the appendicular lean mass index. And sometimes you just have to calculate it and you can always calculate the fat free mass index with both of which we'll talk about. So these are measures of how much lean mass you have or muscle mass in the extremities. And the way this is always reported is total amount of lean tissue divided by height in meters squared. So both appendicular lean mass index and fat free mass index, which is just total mass that is not fat divided by height in meters squared, they're both reported therefore in kilograms per meter squared. So those are the four things you get when you do adexa. And of course, all of these things you want to see how you stack up against a population. And that population is typically stratified by your sex and by your age. So therefore we have nomograms for each of these things and that's how we present the data to a patient. And that's how we therefore make decisions about where you rank and what you need to do.

So to clarify on that, so the bone mineral density, the vat, ALMI and ffmi, those are the four major things. And now I think I've heard you say before, is not every place you get a DEXA scan will give you those metrics, but every place will provide the metrics you need to come to.

The conclusion of that for yourself, with one exception. So there are some DEXA places that only give total body Z score for bone and they don't break it out individually by hip and lumbar spine. This is important because again, I believe I spoke about this on the previous ama, you can't make a diagnosis of osteopenia or, or osteoporosis or frankly assess BMD clinically without that feature. In other words, if you just look at total body bmd, the Z score for the total body is too easy to mask what's going on in those areas. So it doesn't mean you can't get a DEXA at one of those places. You can, but you just have to understand there's a blind spot which is you're not getting adequate information about bmd. So if there's any concern about bmd, you're going to have to go to a place that is able to give the segmented information which is good for.

People to know just because as they're googling different places and calling around it gives them something specific to ask for to get a good understanding.

Yeah.

So on that I think what makes sense to do next is dive into each of those four metrics a little more and kind of what they mean and why they're important. With bmd, as you mentioned, we covered that in in a BMD AMA which was AMA 37 for anyone who hasn't listened to it and wants to go back and listen. I don't think we really need to dive into that in as much detail just based on that ama. But the vat, ALMI and FFMI I think might be worth getting into because I think those are metrics that most people aren't hearing about where body fat percentage, I think everyone is aware of that, they conceptually know what that is. But the other three I think for people not in the space, it's a little outside of their understanding thank you.

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