The Peter Attia Drive - #165 - AMA #24： Deep dive into blood glucose： why it matters, important metrics to track, and superior insights from a CGM

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

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00:00:31.140 So without further delay, here's today's sneak peek of the ask me anything episode.

00:00:39.100 Hey everyone, welcome to AMA number 24. In this episode, I am joined as usual by Bob Kaplan,

00:00:48.280 and we devote the entire episode to a series of questions that focus around glucose homeostasis.

00:00:53.840 We centered the discussion basically around the idea of why one would wear a CGM, especially

00:00:59.800 someone who does not have type 2 diabetes or type 1 diabetes, and we get into the really deep nitty

00:01:05.500 gritty around what is it about glucose that matters so much with respect to health? Why is it that I

00:01:12.220 make such a stink about having lower average blood glucose, fewer peaks of glucose, less glucose

00:01:18.000 variability, and all of the associated things that go with it? So I hope you'll check out AMA number

00:01:23.380 24. And without further delay, here it is. Hello, Peter. Hey, Bob. How's it going? It's

00:01:35.080 going well, man. Ready for an AMA? Ready as always. All right. So in this case, we got great questions

00:01:43.000 about glucose, and we aggregated a bunch. I think it'd be good to do a deep dive. I'm going to go through

00:01:49.240 a couple of the questions here and see what you think. So the first question is more of a statement

00:01:57.120 than a question. I've heard Peter talk about how fasting glucose and even HbA1c measurements can

00:02:02.920 often be misleading and how he favors OGTT, which is short for Original Gangster Time Trial. That's

00:02:11.320 right. Yeah. Okay. Perfect. I think it might be oral glucose tolerance test with insulin measurements

00:02:17.380 and also wearing a CGM to get a better sense of glucose homeostasis. My understanding is that OGTTs

00:02:24.240 and CGMs are typically reserved for people with diabetes. So he's got the following questions.

00:02:29.900 Why does Peter find these tests useful in quote-unquote healthy people? What is Peter looking

00:02:35.420 for when assessing someone's glucose levels? What does he like and hate to see? How does Peter define

00:02:42.680 normal versus abnormal control of glucose? If I'm not diabetic, do I have anything to worry about

00:02:48.660 here? And there's another question that was, are you able to do a breakdown of what you look for

00:02:53.700 on different people's CGM data and what you would advise to improve their numbers, similar to the AMA

00:02:59.120 you did on lab tests? All right. So I'm going to pause you right there, Bob, and I want you to answer

00:03:02.960 this question for me, honestly. Did you pay this person to ask these questions?

00:03:10.660 Asking for a friend. I mean, seriously, these are the perfect questions, the most salient questions,

00:03:19.500 the most important questions. And this might become by extension then one of the most important AMAs we do

00:03:27.520 in terms of the aggregate impact it could have on health and longevity. Because these questions

00:03:34.780 really get at the root of where I think, I hate to use this term, but for lack of a better word,

00:03:41.380 where the mainstream medical system is just so out of sync with what I believe the future of medicine

00:03:47.480 is going to be. So let's take a step back on all of this for a second. Type 2 diabetes has a

00:03:54.100 definition, and it is defined as having a hemoglobin A1C concentration greater than 6.5%.

00:04:00.520 And that corresponds to an average blood glucose. God, I should know this, but the fact that I pay

00:04:05.940 so little attention to it tells you why I don't even know it. I believe it corresponds to an average

00:04:10.700 blood glucose of approximately 130 milligrams per deciliter. And of course, the way it works is it

00:04:18.740 measures the concentration of glycosylated hemoglobin. So it's taking out red blood cells

00:04:25.840 and it's looking at how much glucose is stuck to them. And obviously the more glucose that is stuck

00:04:32.580 to them, the more you can infer that the average concentration of glucose is higher during the

00:04:38.900 period of a red blood cells life. But of course, this is potentially misleading because if a red blood

00:04:45.680 cell has a very short life, for example, I see this in a couple of my patients, including a patient

00:04:52.460 who's recovering from prostate cancer, who still has some GI bleeding issues, patients with gastritis,

00:04:58.980 et cetera, but women with a heavy menstrual period. So people who are losing significant amounts of

00:05:04.220 blood have a higher turnover red blood cells. They're going to have an artificially low hemoglobin

00:05:08.280 A1C. Conversely, people who have red blood cells that stick around a very long time, people with a

00:05:15.340 microcytic pattern, meaning they have very small red blood cells that are less likely to get chewed up

00:05:21.840 in the splenic system, which is where we ultimately break down red blood cells. They're going to have an

00:05:27.760 artificially elevated hemoglobin A1C because their red blood cells are living longer on average than the

00:05:33.920 typical person, which is about 90 days. So that's one reason why I'm not a huge fan of hemoglobin

00:05:39.240 A1C. But the broader point here is that I find it unhelpful to simply say if your hemoglobin A1C is

00:05:48.980 above 6.5 and you have type 2 diabetes, you have quote unquote a disease. If it is below 6.5, you are

00:05:56.060 normal. Or even if we go one step further and say, well, there's a pre-diabetes, which is defined as

00:06:01.180 5.7 to 6.4. And those people we have to watch out for, but anybody at 5.6 and down is completely normal

00:06:09.200 as though there's some enormous difference between 5.6 and 5.7 or 6.4 and 6.5. So while on the one hand,

00:06:16.620 I understand the need to simplify things, I think oversimplification is erroneous. And I think we

00:06:22.780 should view these as a continuum. So glucose at the average level is a continuum. And as the person

00:06:32.120 who asked the question noted, I am a far greater proponent of CGM. Now, Bob, I don't know if you're

00:06:39.000 wondering what this thing on my arm is, but in case you are, this is a CGM. This is a continuous

00:06:44.800 glucose monitor. And as its name suggests, it measures glucose continuously. And while I do not have

00:06:51.880 diabetes, and while most of my patients don't have diabetes, many of them, along with I, wear this

00:06:57.640 device. And I think what we'll get into today is the why. So what are the metrics we're tracking here?

00:07:03.380 And what are we describing as ideal and optimal as opposed to acceptable along those metrics?

00:07:11.200 Anything else I can say broad strokes before we jump into the nuts and bolts of this, Bob?

00:07:15.840 No, I think that covers that other question about the continuous glucose monitor. Wondering if it's

00:07:20.800 like streaming? Or does it actually take measurements every certain period of time?

00:07:26.180 Yeah. So actually, I thought it would be helpful, Bob, to just sort of show you and obviously listeners

00:07:29.880 kind of what this looks like. So it connects to your phone. And every five minutes, it is spitting out

00:07:35.600 a number. If you look at it in a 24-hour fashion, when you turn your phone on your side,

00:07:41.300 you get sort of the 24-hour tracing. So for my last 24 hours, I've averaged about 90 milligrams

00:07:48.480 per deciliter. And my variability has been about 9 or 10 milligrams per deciliter, or my standard

00:07:54.920 deviation. My peak level has been, let me see, I have to go back and look. My peak was 102. And by

00:08:04.740 extension, then I've had no peaks above 140. That's going to come up later on. So obviously, if my peak

00:08:10.420 was 102, I was never above 140. And my nadir was 77. So range of 77 to 102. So anyway, that's the kind

00:08:19.020 of data you get out of these things. And obviously, they have reports that will spit out your average

00:08:24.380 blood glucose over one day, seven day, 14 days, 30 days, 60 days, 90 days, et cetera, along with the

00:08:30.640 standard deviation and things like that. And the way these things work, of course, is they're not

00:08:35.420 actually measuring in the blood. They're measuring in the interstitial fluid. And that, of course,

00:08:40.100 is the remarkable technology, right? It's that it's able to impute what the glucose level is

00:08:45.740 in the blood without actually having to sample the blood. That's the magic of these things.

00:08:50.580 Knowing you, I suspect I already know the answer, but I'll ask it anyway. Have you looked at your CGM

00:08:55.580 and compared, say, like your three-month data to your HbA1c?

00:09:00.900 Of course.

00:09:01.380 Yeah. And there's no comparison. So because I actually have something called beta thalassemia

00:09:06.780 minor, or I carry the trait for beta thalassemia, I have tiny little red blood cells, or as my

00:09:13.840 roommate in med school, Matt McCormick, used to call it, shite for blood. The size of my red blood

00:09:18.260 cells is very small. So my mean corpuscular volume and mean corpuscular hematocrit are very low.

00:09:24.700 I'm not anemic because I make up for it by having a lot of them. So I have a lot of red blood cells.

00:09:29.320 They're just all very small. So I have normal hemoglobin hematocrit oxygen carrying capacity,

00:09:35.040 but my hemoglobin A1c always runs high. I've measured it as high as 5.8. The lowest I've

00:09:44.840 ever had measured is 5.1. But anytime I've measured it, because I've been wearing CGM for almost six

00:09:51.260 years now, if I go and check my A1c versus my trailing 90-day CGM, it almost always suggests

00:10:01.340 that the hemoglobin A1c is higher by 0.5 to 0.8. If I measure a 5.7 on the hemoglobin A1c,

00:10:13.120 it's overstating my blood glucose and it should really be about a 5.1 or a 5.2. And we see the

00:10:21.020 opposite in some people. We have some patients where their CGM is actually showing us a much

00:10:26.840 higher level of average blood glucose than what their hemoglobin A1c predicts. So it's important

00:10:32.560 to understand hemoglobin A1c is a measurement that predicts average blood glucose. CGM actually gives you

00:10:41.040 average blood glucose and you can reverse engineer an imputed A1c. It's obviously the latter that is

00:10:47.100 much more interesting because you're directly measuring the variable of interest. Yeah, it's

00:10:51.580 amazing. I mean, it's amazing technology. It's the difference between like a snapshot and a movie.

00:10:57.280 Yeah, entirely. And from when I started wearing these things nearly six years ago, I thought,

00:11:01.580 I don't know why everyone in the world isn't wearing it, notwithstanding the cost and the logistics

00:11:05.860 of it. And the obvious reason why everyone wasn't wearing it was their cost prohibitive. And

00:11:10.000 certainly back then they were quite involved, but they're getting better and better and better.

00:11:15.040 And I'd like to believe that there will be a day when you go to your first visit at your doctor

00:11:19.940 or prior to your first visit with your doctor, they mail you a CGM and you wear it for 30 days.

00:11:25.580 And that data is looked at by your doctor and your doctor. By the time you arrive in the office,

00:11:30.060 he or she has that information. And instead of looking at an A1c or a fasting glucose, they can really

00:11:36.080 look at what your glucose excursions have looked like over a period of time in the real world.

00:11:41.840 They do that with, I guess if things look fishy, but they'll do it with sphygmomanometer. They'll

00:11:46.020 send you home with a blood pressure monitor and you'll take it every so often, maybe three times

00:11:50.760 a day or whatever it is to get a look at your blood pressure that way.

00:11:53.800 Right. We do that with our patients. Most of our patients, there's a particular blood pressure monitor

00:11:58.020 we fancy and we have them keep it at home. We have a special log. We have a method that we want

00:12:03.580 them to go about doing it, recording it, and we'll track that as well. Unfortunately in the wearable

00:12:08.880 space, blood pressure is still far from prime time. We've tried a bunch of the wearables in that

00:12:14.860 space and have not been impressed yet. I think there's going to be wearables in the blood pressure

00:12:18.680 space soon. Okay. So where do you want to start on this? Because I know that part of the question

00:12:24.320 that was posed is what are the metrics that we track? I want to go back and state my thesis,

00:12:31.100 right? Or call it my hypothesis, I guess. My hypothesis is that outside of the formal diagnosis

00:12:39.080 of type two diabetes. So now I'm referring to what the person asking the question called as

00:12:45.700 quote unquote normal people. It's important that we leave quotes on that because I'm going to argue

00:12:50.080 that that term has no meaning. But in the non-diabetic, which may be a better way to describe it,

00:12:55.840 what is my argument? My argument is the following. Lower average blood glucose is better. A hemoglobin

00:13:04.040 A1C of 5.1 is better than a hemoglobin A1C of 5.5, even though neither of those people are anywhere

00:13:11.580 near having type two diabetes. Two, the more you can minimize glucose variability, the better. And of

00:13:18.540 course, glucose variability is very difficult to measure without a CGM. Using a CGM, the standard

00:13:23.420 deviation is the obvious mathematical tool to do that. And lower is better. Stated another way,

00:13:30.360 if you have two people who both have an average glucose of 100 milligrams per deciliter, which by

00:13:36.180 the way, corresponds to about a hemoglobin A1C of 5 to 5.1, which would be excellent. And one of them

00:13:43.620 has a standard deviation of 10 milligrams per deciliter. And the other one has a standard deviation

00:13:48.260 of 20, the person with the lower one is better off. Third, minimizing glucose peaks is important,

00:13:56.620 irrespective of the first two things I said, average glucose and variability. Although obviously,

00:14:03.320 the more peaks you have, it's going to all things equal push up glucose, and it will certainly increase

00:14:08.860 variability. But I would argue specifically that glucose peaks are problematic and that we want to

00:14:14.760 minimize them. Getting a little bit ahead of myself, what are the three metrics we are constantly

00:14:19.300 tracking in our patients? And what am I constantly tracking in myself?

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The Peter Attia Drive - June 14, 2021

#165 - AMA #24： Deep dive into blood glucose： why it matters, important metrics to track, and superior insights from a CGM

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