BMI vs. Body Composition: What Your Weight Doesn’t Tell You

Dr. Mike: Hey, do you know your body composition? Well, stick around to learn why it's important and how it may help you live forever…ish.

Live Foreverish Introduction: You're listening to Live Foreverish, a show dedicated to helping you live just a little longer. Here [are] your hosts, Dr. Mike and Dr. Crystal Gossard.

What Is Body Composition? 00:00:16

Dr. Mike: All right. Welcome to Live Foreverish. Dr. Crystal, I think most people know we're talking about body composition. I think most people obviously know how much they weigh. I would say [most people].

Dr. Crystal: Most people. Give or take.

Dr. Mike: Give or take. Yeah. Or if people don't, they don't want to know. Let's just say most people know how much they weigh. But most people don't know what those pounds mean.

Dr. Crystal: Yes, it could be bone. Maybe you’re “big-boned.” That’s what they used to say to some people.

Dr. Mike: Yeah, but we're finding out that a lot of that is kind of true.

Dr. Crystal: Muscle, fat. Absolutely.

Dr. Mike: Yeah. That's what we're talking about today. [It’s] more than just knowing your weight—more than just knowing BMI.

We're [going to] talk about some of the issues [of] just going by BMI. But this is really about body composition. It's referring to the percentage of bone, fat and muscle in the body—and how all of that is making up your body composition and weight and all that kind of stuff.

Dr. Crystal: Yes. And the ratio or the percentages of all of the above can impact health.

Dr. Mike: Yeah. We have some information about the BMI in general here, talking about what it is: It's basically your weight relative to your height. That's all it is.

Based on the intro of this show, it's missing all that other stuff. And so right there, you know there [are] issues with it.

Dr. Crystal: Yeah. There [are] definitely limitations with BMI. I think we will talk about a new definition that’s on the horizon to categorize what is considered, I would say, “healthy.”

BMI is designed to help define a healthy weight, what's considered overweight [and] what's considered obesity in the different classes of obesity. And looking at [it] through the lens of obesity as a disease.

Dr. Mike: Right.

Dr. Crystal: And BMI is used to give us those defining parameters.

Dr. Mike: Right. By the way, I want to make sure people understand that the BMI still has—even though we think there [are] limitations with it—a place. It's still a good, standardized thing to use in research and stuff like that. And that's really where I think it's used the most.

It's just going beyond that and understanding more of the impact of everything else. What are those pounds? The muscle? The fat? And really thinking about body composition. I think it's a complete picture that way versus BMI, which is not.

Dr. Crystal: Correct.

Why Is Body Composition Important for Your Health? 00:03:10

Dr. Mike: All right…I want to get into ways that we can measure body composition. If we're telling people that body composition is a better marker [of] overall health, risk and that kind of stuff, how are we testing this? Is it something I can just look in a mirror and go, “Oh, my body composition is this.” What do I have to do?

Dr. Crystal: Yeah, I think sometimes you can look at someone and you can see that they are very lean. Their muscle mass is very visible to the eye.

But often an individual will need to undergo some of these other types of measurements. The first one—which I love, I think it's a good solid indicator—is [the] abdomen-to-hip ratio.

Dr. Mike: Absolutely. Big one.

Dr. Crystal: That's a big one. It's very simple; it's relatively easy. You can measure it yourself.

I know it's a little uncomfortable to have someone else measure it—I guess I would say that. You don't see this in your doctor's office—[like your general practitioners]. I'm really surprised. I don't think I've ever had a doctor perform this test.

Dr. Mike: I never have. It actually has been shown to be a better indicator of cardiovascular issues than just BMI or anything else.

Dr. Crystal: Absolutely. You're taking the measurement—if you want to do this at home—right around the navel and the widest circumference of your hips. And then, you just divide them.

When you're looking at your numbers, men who have an abdominal-to-hip circumference ratio [of] more than one or women [with] greater than 0.85 have an increased risk for cardiovascular disease, diabetes and cancer. So again, we're looking at how you're distributing the fat that you may be carrying.

What Are the Limitations of BMI in Assessing Health? 00:05:38

Dr. Crystal: Is it in the central obesity, or is it more in the hips and thighs? If you have more fat in your hip and thigh area, that's not as high [a risk as] having the abdominal fat. That is better than just getting on the scale, taking your weight and height, and then you have your BMI. Now you're looking at different shapes.

Dr. Mike: It's possible in these scenarios that somebody could have a BMI that says [they're] overweight, but their waist circumference [may not be] so bad. It doesn't mean there's no fat there, it's just in a place where your risk may be a little less than somebody else at central [obesity].

Dr. Crystal: Absolutely. I can attest to this. Being African American, you do find that the BMI is certainly not the best indicator looking at how and where we carry our weight.

Dr. Mike: We already know BMI is really good and helpful for a taller, slender person. Someone [who's] 6 ft [and] slender most of their life, BMI is fine for that person. Somebody like me, 5 ft 6 in, forget it. It's not going to give me something appropriate.

Do you remember Dave Tuttle, [who] worked with Life Extension [years ago]? We laughed one time because he shared with me his BMI. I'm going to tell you what his BMI was—he was obese. But it was because he was 5 ft 6 in and had so much muscle. He was a bodybuilder.

Dr. Crystal: He was a bodybuilder.

Dr. Mike: He literally was a bodybuilder. He was amazing-looking. But based on BMI, he was overweight. I mean, he was obese.

Dr. Crystal: We do know that it's pointless if you are athletic, fit [or] building lots of muscle. Then it's not appropriate.

Dr. Mike: So, the abdomen-to-hip ratio. Fantastic. Great place to start. That's something you can do in your bathroom. You can keep track of that once every few months or whatever your goal is—whatever you're trying to do. It's just a nice number to know.

You should let your doctor know: They should know that number. It should be part of your basic exam. Number two is skin fold measurement. This one's not fun.

Skin Fold Measurement 00:08:12

Dr. Crystal: It's not fun at all. This is something I had to deal with. I've had both the abdominal hip-to-waist ratio as well as the skin fold measurement.

You see all of this in the gym. The moment you sign up with a fitness trainer, they pull out the calipers, and you're like, “Okay,” and [you] put your arm out. And they are pinching fat. Different parts of your body. Lift up your shirt, please, and now let me pinch your waist.

Dr. Mike: The old, “Can you pinch an inch?” thing.

Dr. Crystal: “Pinch an inch.” Oh, I've been traumatized [by] that too. When I was a cheerleader in college, our coach said, “If I can pinch an inch, you're not cheering.” So, talk about traumatic experiences there.

Dr. Mike: And most of the time, they're doing this at the triceps.

Dr. Crystal: Triceps, yes…Arm down, and you're pinching the back of the tricep. But also on the stomach, you get the pinching sometimes. To get a more accurate reading, you will find people pinch multiple locations.

But occasionally, you'll just get the one tricep with the skin fold caliper. But I'm telling you, it's not really accurate. If you have one person, they have their technique down, and you get your measurement. And then, maybe six months [or] a year later, you measure it again by the same person—then maybe it's accurate.

Dr. Mike: Accuracy is a tough one on this one. You [have to] make sure it's been done right, which is important with really anything that you do. You [have to] make sure, even with the abdomen-to-hip ratio, you're measuring across the navel every single time.

Don't look at yourself and say, “Well, if I just drop this down a little bit, then a couple [of] inches come off.” No, you can't do that. You [have to] be honest with yourself.

It's the same thing with skin fold measurement. I can tell you when skin fold measurement won't work.

Dr. Crystal: When?

Dr. Mike: In Texas, we used to call it Dunlop disease. When your belly Dunlop over your belt buckle. Because those guys—we call [them] “beer belly guys”—all of their fat [is] central. They sometimes have the skinniest arms. If you're measuring tricep in those people, you'll be like, “Oh, you're fine,” but you get their guts coming all out. For them, it might be better to do gut side—something like that.

Dr. Crystal: The whole purpose here, again, is to try to estimate your body fat. It's typically considered to be in excess when it's greater than 25 percent in men, and if your body fat is in excess of 30 to 38 percent in women.

Body Fat Percentage Guidelines 00:11:20

Dr. Mike: Yeah. And the caliper tells you that. People are trying to figure out where that number comes from. It's on the caliper that's pinching. Based on how much it goes in or how much it doesn't, you can look at the [percentage]. It shows you on the caliper.

Dr. Crystal: Well, it's an equation. So, you're putting it into an equation. It's measured in centimeters, and then you plug it in.

Dr. Mike: And they tell you how to do that if you get a caliper.

Dr. Crystal: Yes. I mean…I'm not going to do this on myself.

Dr. Mike: You're still traumatized.

Dr. Crystal: I think there are other ways, which we'll talk about next.

Dr. Mike: Let's go. Bioelectric impedance analysis. That sounds fancy.

Dr. Crystal: Yes. Now, when I was a personal trainer, I did this on every new member who came in. I gave them an assessment, and we used this little machine. You had to hold the machine out in front of you. At first, you had to make sure they were hydrated, not dehydrated. It's another way of measuring body fat.

The way it's working is [that] the body's mostly composed of water—those ions. So, it's sending an electric current through your body. And we know that the current flows more readily through muscle and bone versus fat.

Dr. Mike: Fat’s going to impede that current. And you'll see that current drop.

Dr. Crystal: After it takes the measurement, it will shoot out the reading on your percent body fat right there on the machine. So, you don't have to do any calculations. Obviously [there are] some challenges there: if you do the hand version, it's going through one hand and out the other side.

Dr. Mike: Right. So, you're holding these things…

Dr. Crystal: If your upper body is lean versus [your] lower body, then that throws off the analysis.

Dr. Mike: Like the Dunlop disease.

Dr. Crystal: Right. There are some where it's doing your feet—like you stand on [an] electric current metal plate.

Dr. Mike: When you were looking at a client when you were doing this, did you ever change it up? Like how you did it?

Dr. Crystal: No, we didn't have the metal plate version that you stand on. But some places now have both where you're standing and holding.

Dr. Mike: You would utilize that based on just looking at them. We should do the feet with you, and you can do the hand.

Dr. Crystal: If you are dieting, we know you tend to lose muscle. Or if you are incorporating weight training [or] resistance exercise, it's nice to see that your body fat percentage is decreasing.

Dr. Mike: Listen, all that [is] biofeedback. It's encouraging [and] motivating. Even if your weight's not dropping as much as you want but [your] body fat percent is getting better—that’s motivating.

I think with these types of machines, though—because these are currents—you [have] to be careful about using different machines. First, you [have to] calibrate them—number one. Calibration should bring all machines to a standard, but they're still all a little different. And so, it's probably also better to do the same machine.

Dr. Mike: Every single time.

Dr. Crystal: If you can.

Dr. Mike: Just like with weight scales. Don't worry if your scale is off a couple [of] pounds. If that's the one you got your baseline on, fine. Keep doing that one because it's going to measure the difference or the change in weight. Same thing here.

Dr. Crystal: Yeah. So, just another strategy to identify body composition.

Dr. Mike: This one seems nicer.

Dr. Crystal: It is. Definitely. Hands down. I prefer that over someone telling me to lift my shirt so that he can pinch my fat.

Dr. Mike: Look at all that! Look at this. We [have to] get rid of this.

Dr. Crystal: Gosh! It's horrible.

Dr. Mike: That right there might make me want to go, “Bye.”

Dr. Crystal: I'm not doing it. I don't blame you if you don't want to.

Dr. Mike: Yeah. So that's better—that's bioelectric. Are these available for home use?

Dr. Crystal: You can. Yes.

Dr. Mike: Do you have one at home?

Dr. Crystal: I don't.

Dr. Mike: That's surprising.

Dr. Crystal: I don't. We're going to talk about this, Dr. Mike. We're having this conversation, but a lot of these things I don't dwell on personally. I'm just all about doing things that can help my health. Obviously, to me, that's my focus—healthy habits. I think it will all fall [into] place.

Dr. Mike: I agree, and I love that because this stuff, you can get obsessed with. It becomes more important to be good on the test than it is just about your health. I think you're right.

One of the reasons we wanted to talk about this, though, is to bring up the idea that there [are] multiple ways of measuring how you're doing on that health journey. Sometimes, just the weight [or BMI are] not giving you the full picture. So, there are some of these things you can do where the picture becomes [clearer].

Dr. Crystal: Absolutely. Because it can be very discouraging if you feel like you're on the right track, and you may not be seeing changes on the scale. And just knowing that scale is not telling you the full picture.

Dr. Mike: But maybe with bioelectric stuff, you realize, “But I have gotten a little bit better.” That can be encouraging as well. If you start getting mad at this process and start getting mad at a machine, put the machine away and just go be healthy. Go do your exercise and stuff like that. Just don't get so crazy with this because we're also going to talk about some other things you can do that are quite expensive.

Dr. Crystal: Oh, yes.

Dr. Mike: The next one coming up: air displacement. This is about $120 per test. And it's usually not just one test, as far as I remember. It's used in the military; it's used by professional athletes. So, it's a different group. Most people probably don't need to be doing [it].

What Are the Most Accurate Methods for Measuring Body Composition? 00:18:06

Dr. Mike: What do you think?

Dr. Crystal: I would say no. You're right…[But] we have people with different personalities [and] health goals. If you are all in living forever…ish on this longevity, anti-aging path, and you want something that's more accurate than the assessments that we've talked about thus far, this is something [to consider].

And you're starting to see these machines in some of your health spas [and] your med clinics. They're offering these services. You just go in and you just sit in this chamber.

Dr. Mike: It's a sealed chamber. And basically, it's just measuring how much your body displaces air. Think of a sail: air hits the sail; it displaces that. That's one of the reasons you move. The bigger the sail, the more displacement. The same thing with your body—if you're too big, you're going to be displacing a lot of air.

Dr. Crystal: Yep. So, it's another option. You may see it on your timeline…

Dr. Mike: I don't know. I think the bioelectric sounds great. So far, for me, the two are: the abdomen-to-hip ratio—number one; number two, the bioelectric. I think those two sound reasonable.

Everything else here, we'll see. Now, we're going on to—what are we calling these—these are medical-grade options for measuring body composition. They're accurate.

Dr. Crystal: They are. And we see this sometimes when we're looking at some of the studies that we review for weight loss. And we [say], “Oh, they performed a DXA on these participants. Okay, we can trust these results.”

Dr. Mike: Yeah. These are tests that are often done in the studies. Done with professional athletes. A lot of Olympians do these things in [preparation] for their events. One of the reasons that they're at this level is the accuracy. You can really count on these to be consistent from test to test to test. That first one you said it is DXA.

Dr. Crystal: Yes.

Dr. Mike: Same thing for our bones.

Dr. Crystal: Right. Exactly. And so, that's really nice to see. If you have access to this, then it's just another way to give you estimates of bone mineral density and adipose tissue. I’m sure you're familiar with some of the others.

Dr. Mike: If your doctor only orders a DXA for a bone, it's not completing the picture. Your radiologist is not looking at anything else. It's not titrated right for the tissue.

If you're just doing bone, even though it's DXA, it's a little different. You have to be clear that this is not for bone density, it's for body composition. It's a slightly different test—same machine. But the dials, you change them a little bit. And that allows you to do body composition.

Dr. Crystal: I could see how this can be very important for individuals as they're getting older, like [the] elderly, because we see weight loss in those individuals. They're losing bone, but they're also losing muscle—and we [try] to identify the extent of that muscle loss to see if they're what we sometimes call “skinny fat.”

Dr. Mike: That's right. That's a newer thing that we're hearing, like the “skinny fat” condition of older people.

Moving on to the next one: an MRI. MRI is going to be great at distinguishing fat [from] muscle. I mean, that's what it really is going to be good at. And so, again, a lot of athletes do this. They want to see the fat go down [and] the muscle go up—it’s mostly looking at skeletal muscles.

If you're going to do the MRI for this, you're probably focused on larger muscle groups—you're probably focused on thighs, lower leg, chest [or] arms.

Dr. Mike: I'm not sure how much they do the abdomen here. I guess you could, but there [are] so many organs in the way that's going to make it a little bit harder to test. But that's my guess…

But I can see how this can be used if you're trying to build muscle, and you really want to measure that result. Maybe if you're a boxer, wrestler or whatever that may be, that might be useful for you.

Now, quantitative MRI, it's just a little [fancier]. That's all. It allows you to make better calculations of fat-to-organ-to-tissue-to-water ratios. It's more accurate.

Dr. Crystal: All right.

Quantitative MRI 00:23:27

Dr. Mike: That’s all it is—it’s just a little more accurate. Not cheap. The software for this is not cheap.

Dr. Crystal: Well, I can imagine not. I got an MRI a few months back, and it was almost $400. It was not covered by my insurance.

Dr. Mike: A qMRI could probably be 50 percent more, maybe even double. It's expensive. The original ones were called EchoMRIs. They were used a lot [on] people who were cachectic and trying to measure the rate of cachexia, which is a wasting disease [commonly associated with] HIV. I think that's where it was mostly used in the 90s. And [with] chronic infection. So yeah, it's just expensive.

Dr. Crystal: And then there's underwater weighing. I remember learning about this years ago.

Dr. Mike: This is kind of old. This is old school.

Dr. Crystal: Yeah, these are old school techniques that you see [at some of those] Division I athletic programs, where they have kinesiology studies and sports medicine. I remember learning that this is the best way to estimate body weight [and] volume.

Dr. Mike: I don’t think I’ve ever actually seen this done.

Dr. Crystal: I've seen it in pictures when I was learning about it.

Dr. Mike: So, I guess you have to be completely submerged.

Dr. Crystal: Yes.

Dr. Mike: What are we measuring? Water displacement versus [air]. Because we already talked [about] air. Is that what we’re measuring?

Dr. Crystal: Water displacement.

Dr. Mike: Okay. So, this is water versus air. I'd rather do the air. Some people can't hold their breath. How long do you [have to] stay under?

Dr. Crystal: I don't know those details.

Dr. Mike: A lot of these things are used in research, used by professional athletes in very specific conditions [and] chronic conditions that we even mentioned. [It’s] expensive. Is it absolutely necessary? No. But if you're really into that stuff, go for it.

Dr. Crystal: Yes, if you want to know this information. I think also understanding there [are] levels. So, that's why we started with the abdomen-to-hip ratio—something you can just get a measuring tape [and] do it at home.

You can do the calipers at home—very simple. Then the next level. Because [what’s] going to happen—and the reason we're going over all of these different options—is you will read about each option and then read about [its] limitations. People will say, “This is inaccurate.” So, there are levels of getting more and more accurate. And so, for the person [who] is the overachiever and wants the best of the best, I would say go for it.

Dr. Mike: Go for it. Just make sure if you're going to measure your waist, do it correctly. Whether you're using a measurement around your waist or the caliper, you [have to] grab that fat. You can't cheat and grab a little bit of it. You [have to] really get it. Because we like to cheat ourselves, don't we? “Oh, look, it got better.” [But] you barely pinched anything on it.

Dr. Crystal: Yes.

Dr. Mike: So, you’ve got to be honest. If you're really going to do all that. But, I think you're right—don't let this stuff take away from the focus of the healthier lifestyle. Good food, good social interaction, being active—we're not even [calling] it exercising, just [being] active. Find that thing that you like to do and get outside. Even if it's walking, walking's fantastic.

Do that stuff, and as you said, a lot of this will fall into place. Things will improve for you; I do think [so], over time. That's your focus. And these things are simply tools that [may] help you get there faster or [with] better results. But that's all they are—they're just tools. They're not the end game.

Dr. Crystal: They're not the end game. The whole purpose behind all of this is to reduce your risk for chronic disease, cardiovascular disease, cancer, arthritis [and] sleep apnea. But there are many factors that go into the development of those, and weight is just one. There are some people [who] may be heavier, and they aren't dealing with [that].

Dr. Mike: You see that.

Dr. Crystal: Right. They're not dealing with a chronic systemic disease state. I just wanted to point out that we are very well aware [that] we're not promoting that weight is ultimately your issue.

Dr. Mike: You're spot on. Because even as a clinician, it's well-known that if a patient comes in—let's say you never met this first-time new patient—[and] the person looks decently lean, you don't ask them anything about diet. You don't say anything about it, yet you don't know if that [person is malnourished].

Dr. Crystal: Do they have an eating disorder?

Dr. Mike: Maybe they're skinny, but maybe they're still eating junk.

Dr. Crystal: Right.

Dr. Mike: And maybe there is inflammation and all that. But yet if somebody looks just a little overweight, it's like, “Well, we [have to] focus on that.”

Dr. Crystal: I know. I think that's horrible.

Dr. Mike: Right, there is a discrepancy and bias. Weight is just one issue of overall health. [There are] so many other components to it. Don't just get stuck on that scale.

Dr. Crystal: Yeah.

Dr. Mike: I think this is great, there is some more information about BMI. BMI [is] getting improved and all that kind of stuff. I don't know if I want to dive into all that, but at the end of the day, BMI is just another tool.

BMI as a Tool 00:29:35

Dr. Mike: It's just tools—that’s all these things are. First of all, our sponsor, Life Extension, [wants] to say thank you. If you go to LifeExtension.com, you can go ahead and use the discount code…

Dr. Crystal: “PODCAST.”

Dr. Mike: Is that how we're saying it for 2025?

Dr. Crystal: Podcast.

Dr. Mike: But not podcast. You'll get 10 percent off when you spend $50 or more, plus free shipping and handling. That's “PODCAST” at LifeExtension.com.

A great place we can also send people to is our health education hub. That's LifeExtension.com/Education. Great place to go—a lot of articles there. So, check all that out as well.

We appreciate you guys listening. Don't forget you go to LiveForeverish.com and download a bunch more episodes. And when you do, please like, share and comment. We really appreciate that type of engagement. Whenever you're at, if you can give us a ranking, that's big now, too. We [have to] be ranked; [we have to] get some stars.

So, give us some stars. Wherever you listen to us—whatever your aggregate is, as they say—go ahead and do that. We do appreciate it. That's at LiveForeverish.com. I'm Dr. Mike, that's…

Dr. Crystal: Dr. Crystal.

Dr. Mike: Thanks for listening.