The Bone You Have At 50 Was Built Before You Turned 18

0:00When we talk about childhood obesity, the entire public conversation is about adipose tissue. How much is there? Where is it? How do I get rid of it? But no one asks what's happening to the skeletal muscle underneath. Adolescence is not a period when bone is maintained. It is a period when bone is acquired.

0:17Dr. Gabrielle Lyon:In the four years surrounding peak bone mineral accretion, children lay down close to 40 % of the total body bone mineral they will ever carry.

0:31Children with obesity are frequently weaker. They have more muscle, but not quality tissue. Pediatric researchers have started calling this sarcopenic obesity. A child can have a larger quad and a lower capacity to use it

0:47Dr. Gabrielle Lyon:because bone acquisition is time limited and the deficit, you don't feel it, it's silent. Fracture arrives without a warning. If you're not training, can you overcome that? I'm not sure. But now we swap obesity for GLP-1 use and what happens to our children who are growing both bone and muscle. Here's what the literature points towards.

1:19Lately, I've been getting a lot of questions from my current patients about their kids. Patients are asking me if they should be worried about their kids' weight and or what to do if their kids are a little pudgy. So if you're a parent and you're worried about your child's weight, then listen up for some of my thoughts. Now, I feel like we're at a crossroads. And for the longest time, we've asked the question, what will happen to my child if they lift weights? instead of asking what will happen to my child if they don't. Now, imagine a world where in one direction, everyone is in a chair that flies around like in Wally versus imagine this, a 29-year-old woman steps out of a taxi, sets her foot on the curb and her weight lands wrong.

2:14She hits the pavement. She fractures her hip at 29 years old. Now, nothing on her chart explains it. Her body weight sits in the normal range. She is not on steroids for any kind of lung inflammation. She doesn't have cancer, no metabolic disease. You get the picture. No history that would put a fracture like this anywhere near the differential. What she has in line with her history from 15 years earlier when she was a teenager is she had anorexia nervosa. She got treatment, she recovered, her weight came back, but her bone did not. She spent the single window, not intentionally, in which a human skeleton is built, not building, but is built.

3:07And the body does not offer that window twice, unfortunately. Now, I want to be very, very careful here because I am not telling you this story to frighten anyone and I'm not telling it to litigate a disease that is far more complicated than a lecture about nutrition. I am telling it to you because it is the cleanest example that I can think of. and I know of a principle that runs through everything I'm going to say for the next 20 minutes. What a child builds is what an adult gets to spend, especially when it comes to bone. Now, before we get into this episode, if you or someone in your house is in the middle of an eating disorder right now, this episode is not treatment.

3:54This is not an eating disorder episode. I'm going to recommend, again, I'm not your physician, but there's a National Alliance for Eating Disorders helpline, and I strongly would consider getting professional help. This is a podcast on childhood obesity. What happens when we go to the extremes, like with GLP-1s? We are seeing this all over Hollywood. But what is the impact of someone who is younger? Welcome or welcome back. I'm Dr. Gabrielle Lyon, and today we're talking about kids. Now, like I mentioned, I've been getting a version of the same question from my patients in my practice for months now.

4:32And it usually comes out sideways in the last two minutes of a visit that was supposed to be about them. It goes something like this. My son is getting soft. My daughter is on medication now. Is it okay if she lifts? Should I say something? Should I say nothing? Underneath every one of those parents' questions is a parent trying to solve for a body they can see their kid using tools and tools no one gave them. So let me reframe the whole conversation. For about 30 years, the debate in pediatrics was whether it was safe for a child to lift anything heavier than their own body. That debate is finished.

5:11It is done finito. The question that replaced it is the one we need to ask more of. What happens to a child who never builds strength at all? What happens to a child who doesn't lift weights? This is an episode where we're going to go through what a muscle problem looks like in a child, what screens are displacing and what GLP-1 receptor agonists are doing to muscle and bone in a growing skeleton, and what the training and nutrition response should be. I will hand you a protocol at the end, should you choose to execute it or not. I'm not your doctor, but I'm here to educate. Okay, let's start with a piece that gets missed.

5:50When we talk about childhood obesity, the entire public conversation is about adipose tissue, fat tissue. How much is there? Where is it? How do I get rid of it? But no one asks what's happening to the skeletal muscle underneath. Here's what the literature points towards. Children with obesity generally carry more absolute muscle than their normal weight peers. Yes, they do. Bigger muscles, larger cross-sectional area. Now, if you stop there, you would conclude like many people have that those kids are stronger. But when you measure relative strength, meaning force production per kilogram of body weight, the flip flop is observed.

6:31The research suggests these kids are frequently weaker and there's evidence of impaired oxidative capacity within the muscle itself, which makes sense. What is happening is they have more muscle but not quality tissue. And that is this terminology trap that the whole ballgame starts with. Muscle mass is not just muscle mass. It is not muscle strength and it is not muscle quality. A child can have a larger quad and a lower capacity to use it. Pediatric researchers have started calling this sarcopenic obesity. And I want to hedge this appropriately because it's what I would consider a new sarcopenic phenotype because the field does not yet have a consensus definition.

7:23Reported prevalence ranges across published studies are enormous. Now we're talking about sarcopenic obesity in kids. So this is not well studied. This phenotype is not totally agreed upon. So I would treat any specific prevalence figure you find with some degree of skepticism. What is more consistent and what I find more persuasive is the direction of the associations. So what does that mean? Lower relative muscle mass in kids tracks with the following, higher cardiometabolic risks with fatty liver severity and systemic inflammation and with mental health outcomes. different cohorts, different methods.

8:10But again, it's the same direction. These are associations. And when there's a preclinical finding that I just haven't been able to put that down. Now, this is in a rodent model. For example, in juvenile mouse model, obesity during development appears to impair muscle growth through changes in gene expression. Again, this is in a rodent model, but with myogenic programs suppressed and adipogenic pathways switched on. So in layman's terms, basically, if an individual has unhealthy muscle when they are young, that it impairs the muscle potential throughout adulthood, and it switches on fat building pathways.

8:59Again, this is just the idea. And the part that matters is those muscle deficits persisted after the animals successfully lost weight. The fat came off the muscle deficit state. Again, this is a mouse and I'm not going to stand here or sit here on your screen and tell you that it transfers cleanly to a 12-year-old boy. It does raise a hypothesis and mouse models and epidemiology are used for hypothesis generation, and we should be taking it seriously, which is the following, that the developmental window may not be able to be recovered to the potential that it used to, which is exactly what the woman in the taxi taught us about bone.

9:46She had suffered from severe restriction, which again, maybe that's going to happen with the GLP-1s. But now we swap

9:55Dr. Gabrielle Lyon:obesity for GLP-1 use and what happens to our children who are growing both bone and muscle screens. Let's talk numbers first. School-age children and adolescents in the U.S. are averaging north of, get this, seven hours a day of recreational screen time. This is on top of schoolwork. This is pandemic era, pushed total daily screen time exposure close to eight hours, up from roughly four and a half before. And what's so important is it hasn't returned to where it was. Only a minority of young children are meeting the American Academy of Pediatric Guidance at all. Here is where I want to be precise because the causal story is messier than the headline.

10:42Dr. Gabrielle Lyon:No surprise. The American Heart Association has noted that objectively measured sedentary time on its own shows a little consistent association with adiposity once you account for moderate to vigorous activity. Sitting still is not the mechanism. I always think it's fair to present all of the data to the best of my ability. We're not saying that screen time is causing this increase in adiposity directly. Could it be related to activity? Yes. So is screen then associated with it? Well, screen time specifically behaves differently from generic sitting. And that is the interesting part. The association with higher body fat is more consistent for screens than for sedentary time, generally, which tells you something is riding along with screens.

11:35Dr. Gabrielle Lyon:Again, this is association data. Maybe they're eating Cheetos. I don't know. But there are three things that I want to put in order for you. Three candidates that we should cover or three domains. The first is food. Children are exposed to a continuous stream of food and beverages, marketing during screen exposure. And the research on this, it's not subtle. What children see depicted changes what they ask for or what they wanna eat. Now, we all know this. If you're a parent, you see a commercial for Fruit Loops and then you see Fruit Loops in the store with your kids, they're all over it. So food, food choices, food marketing on screens.

12:17Dr. Gabrielle Lyon:Second, this is sleep, which screens degrade in both duration and quality. And sleep loss changes appetite regulation and reduces the likelihood that a kid trains the next day. You and I as parents or you who cares for someone who is small understands that if you personally don't sleep, your appetite increases. If kids don't sleep, their appetite increases. Also changes glucose regulation. We know this to be part of a metabolic picture. The third is displacement. And hours are finite. An hour on a screen is an hour not doing something else like training. And the relationship appears to run in both directions.

13:03Dr. Gabrielle Lyon:So longitudinal work in large pediatric cohorts suggest that television watching predicts weight gain and the higher weight also predicts television watching. There's an intervention point and it's in the loop. We have to break the cycle. So one more finding worth holding onto and noting is that it kills a comfortable belief. In adolescent data, very high physical activity does not appear to fully offset very high screen exposure. So I'm going to let that settle in. Even if you're very active and think about you as you sit at your desk, even if you're very active, it doesn't totally offset screen exposure and low screen exposure does not rescue a child who is inactive.

13:51Dr. Gabrielle Lyon:These behave as two independent levers, meaning you can't just allow a child to be off the screen, but be still inactive. So let's go where the questions are. Semaglutide, semaglutide, however you want to say it, has been FDA approved since 2022 for chronic weight management in adolescents, 12 and older with obesity. In the step teens trial, the mean change in BMI at 68 weeks was a reduction of about 16 % against a slight increase on a placebo. Roughly 73 % of the treated adolescents lost at least 5 % of body weight. Those are not marginal results in a 14-year-old carrying severe obesity with a comorbidity, meaning diabetes or something else already, on the table.

14:44Dr. Gabrielle Lyon:This is a meaningful clinical effect, and I'm not going to say that or pretend otherwise. But let me be very exact about my concerns, what I'm concerned about and what I'm not. My concern goes back to that story that I told you about the 29-year-old girl suffering from anorexia who put her foot down, fell, broke her hip. And my concern is not that the GLP-1 receptor agonists destroy muscle. I'm not worried about that. That framing is sloppy, and I want it out of the conversation totally. There is no evidence of a direct myotoxic effect. What the adult body composition literature shows is that when you produce large, rapid weight loss by way of a substantial reduction in food intake, a meaningful share of what comes off is fat-free mass.

15:34Dr. Gabrielle Lyon:In the DEXA sub-study of step one in adults, lean body mass fell by roughly 10 % from baseline. And lean mass accounted for something on the order of 30 % to 40 % of total weight loss. There's a bunch of problems with this. DEXA is not specific. Fat loss exceeded lean loss, all which is expected and reassuring. but we don't really know how much skeletal muscle and what that effect is. The mechanism there is not the drug. The mechanism is a large energy deficit arriving with, of course, reduced protein intake and no meaningful resistance training stimulus. And this is kind of a terminology trap and it matters enormously because the two framings lead to opposite clinical actions.

16:25Dr. Gabrielle Lyon:If we say the drug destroys muscle, then it leads to people refusing the medication. Weight loss without protein and loading costs muscle leads to prescribing the medication alongside the protein and the loading. And in an adolescent, the stakes shift again because an adult on a GLP-1 is hopefully maintaining and defending tissue they already built. But an adolescent in the middle of building both bone and muscle, we're intervening during an accrual period, not during maintenance. And there are no easy answers, but these are not the same physiological situations. And I've not seen data that fully resolves it.

17:08Dr. Gabrielle Lyon:Adolescence is not a period when bone is maintained. It is a period when bone is acquired. In the four years surrounding peak bone mineral accretion, children lay down close to 40 % of the total body bone mineral they will ever carry. Peak accretion rate arrives at roughly 12 and a half in girls, 12 years old in girls, and 14 in boys on average. Obviously, there is a wide individual variation. By four years after the peak, the great majority of adult bone is already put in place. And the National Osteoporosis Foundation position statement estimates that lifestyle factors account for somewhere between 20 and 40 % of adult peak bone mass.

17:57Dr. Gabrielle Lyon:That number is the entire reason this episode exists. It's a meaningful fraction of a person's lifetime fracture risk. And that is happening right now. So by a set of daily behaviors during a handful of these years, these years will not be able to be repeated. And again, no pharmacology to date can fix that. So what does rapid pharmacological weight loss do inside this window for kids? In adults, the best evidence I know of is a randomized trial published in JAMA open in 2024 in 195 adults with obesity, four arms, all following an initial low-calorie diet, placebo, exercise alone. the lariglutide alone group lost 14 kilograms and showed a decrease in bone mineral density at the hip and the lumbar spine compared with exercise alone.

18:55Dr. Gabrielle Lyon:The combination group lost the most amount of weight of anyone, makes sense, close to 17 kilograms. And their hip and spine bone mineral density was statistically unchanged. That is important because it's one of the cleanest demonstrations of a principle that I've been arguing for years. Guys, come on. The greatest weight loss in the trial came with preserved bone. Exercise was not an accessory to the pharmacology. Exercise was the thing. It was a thing protecting the skeleton while the pharmacology did the work. The American Academy of Pediatrics has supported resistance training for youth since its 2020 statement.

19:36Dr. Gabrielle Lyon:Properly supervised with technique, top before load is added, injury rates are low, and lower than in most of the sports these children already play. The myth that lifting stunts growth has no support behind it, and it never did. A systematic umbrella review of 14 meta-analyses found that resistance training in children and adolescents produce medium to large effects on muscle strength and small to large effects on muscle power beyond what growth and maturation deliver on their own. Lifting weights improves that, makes sense. And the authors were appropriately careful about the underlying quality of the included work.

20:17Dr. Gabrielle Lyon:We'll link that paper. The direction and consistency of the fact, though, is not in dispute. One physiologic detail worth understanding because it changes how you coach a child. In prepubertal children, strength gains are primarily neurologic. Improved motor unit recruitment, improved rate coding, improved coordination, still waiting for my kids to be coordinated, not hypertrophy. An eight-year-old who gets dramatically stronger over 12 weeks has not built appreciable muscle tissue. She's learned to use what she has, which is so cool. This is why load is not the point at this age and why technique and movement competence and consistency are.

21:01Dr. Gabrielle Lyon:Here's what to do. And you can take them in order. Take it or leave it. Number one, change the metric. We shouldn't be tracking our child's weight and start tracking what your child's body can do. Can she hang from a bar? For how long can he carry the groceries and be a good son? Like who knows in one trip. Push-ups, sit-ups, time on the bar. Track those out loud. Make it a household competition. This matters for two reasons. It measures the thing that predicts long-term health and it takes weight out of the family conversation, which we don't talk about weight in our household, which is protective in a house where, you know, there's a risk of developing an eating disorder or anything like that that can take root.

21:44Dr. Gabrielle Lyon:Number two, three days a week of muscle strengthening work, three days a week of bone strengthening work. Again, this is written into the physical activity guidelines for Americans alongside the 60 minutes a day of moderate to vigorous activity. It's in there. It's in the line. People skip. Bone strengthening means impact, jumping, hopping, sprinting, landing. Bone responds to strain rate, swimming and cycling, whatever else it can do. Nah, it doesn't totally load the skeleton. Number three, teach the pattern before you add the weight. Squat, hinge, push, pull, carry, body weight first, then light load, then heavier.

22:22Dr. Gabrielle Lyon:Supervision is the variable that separates the low injury rate in the research from a bad outcome in your garage gym. Number four, my favorite topic ever. Anchor protein at breakfast. The morning meal is the most important. Children eat a ton of carbohydrates and let's get it right. Real protein dose is essential. You can have eggs, Greek yogurt, cottage cheese, meat from the dinner before. Get your protein in. Five, if your child is on a GLP-1 agonist, treat resistance training and protein as part of the prescription. Not a suggestion. Six, put a floor under the screen, not a ceiling. Ceilings are enforcement problems.

23:03Dr. Gabrielle Lyon:Floors are structural. The rule in my house is that something physical happens before we watch movie night. And that screen is off during meals and out of the bedroom. If there's an eating disorder history in your family, in your child, or in you, say so to the pediatrician now because bone acquisition is time limited and the deficit, you don't feel it, it's silent. Fracture arrives without a warning. So I opened with a woman on a sidewalk who couldn't get up. And I want to end there. Nothing about her outcome was bad luck. A hip fracture in a young adult from a fall that should have produced a bruise is almost always a story about a building phase that didn't happen.

23:47Dr. Gabrielle Lyon:Your children are in that window right now, every one of them. And the ones who are suffering from being under muscled, but look totally fine on the outside. This is who I'm worried about. We've spent a generation asking whether it is safe for a child to be strong. That's wrong. It is the wrong question, and it always was. The risk was never in the loading. Muscle and bone are not what a body has. They are what a body was built to become. Build it now. I'm Dr. Gabrielle Lyon, and I'll see you next time. And don't forget to be forever strong, which, by the way, starts in childhood.

24:35For more information, visit www.fema.org