Interview Summary

John, I’m not an expert myself on physical activity, but I’ve been a fan of yours and others in your field for many years. And it just seems to me that it’s a vibrant, active, exciting field where almost every day some new finding comes along that confirms the benefits of physical activity or discusses different ways to do it. Can you give us an overview of why being physically active is such a good thing?

I think that if we could take the benefits of physical activity from a health perspective and bottle them up into one pill, we would probably have the most powerful pill that was ever invented. And I think that the reason for that, Kelly, is physical activity pretty much touches every system of the body. Every anatomical physiological system of the body in some way is touched by physical activity. And as long as you’re not kind of overdoing it, abusing it, the body is adapting to allow you to do that activity. There’s a lot of things that we do where we try to counteract certain things with medications and surgeries. But the one way that we can make the physiology of the body adapt and become healthier, the one real way to do that is through physical activity. And I think it touches so many systems that way, that’s why I think we keep hearing about all the pure benefits that we can get from this activity.

Okay. It sounds like it would be easier to have a discussion on or try to find somewhere physical activity is not beneficial. And it’s interesting that the body makes room for physical activity by adjusting to whatever the demands of it are. I’m assuming there’s some evolutionary reason for this. That people evolved having to be physically active just to get by in day-to-day life. But is that true? Have we inherited something in that regard?

I think we have. And we went from hunter gatherers where you had to take your body and go out and find the food you needed to eat, to we don’t have to hunt and gather very much anymore, at least in the US and other developed countries. The most hunting and gathering we do is go to the fast-food restaurant or the grocery store. The body has adapted to that. And I think that’s one of the reasons that the body is so resilient. Now you think about it, Kelly, somebody who’s had a pretty major coronary event. What’s the one thing that gets recommended for them? Become more physically active, start exercising. And the body starts to bring itself back. Not maybe to the way it was before that, but it helps to regenerate the body in ways that other kind of things just don’t do it. I think that there’s definitely this physiology underpinning that we really need to keep thinking about.

Speaking of coronary events, and you probably know this history way better than I do, so correct me if I’m wrong. But I remember hearing about the important historical role that a cardiologist named Paul Dudley White played with Dwight Eisenhower when he was president. And as I understand the story, Eisenhower had a heart attack, and the prevailing wisdom of the day was let you rest for a really long time after a heart attack. Like the heart was worn out and needed to recover and mend itself. But he reversed that, put that on its ear, didn’t he?

Yes, he did, and I think that kind of laid the groundwork for where we are with cardiac rehabilitation and cardiac treatment along the way. And that was probably the groundbreaking thing that happened where don’t be afraid to start moving. And that has now evolved to diabetes, cancer treatment. You start to name all the conditions where it seems like activity is good. Even if you’ve had these conditions, as you go through your treatment plan.

We’ve focused mainly so far on the physical benefits of physical activity. What about the psychological ones?

I think that there’s probably so many of those too, Kelly, and this is maybe where you know more than I about some of these types of things. But there’s such great data that came out, maybe 20 years ago, where we were seeing studies coming out looking at depressive symptomatology, for example. And some of the stunning findings they were that people, even with known depression, could benefit and actually reduce their depressive symptomatology with at that time aerobic forms of physical activity. I think it’s evolved to all types of different forms of physical activity. So, we have these depressive symptoms that can be dealt with, or maybe even prevented. We’ve seen it with mood and enjoyment, you start to just start going down the list. And I think the most evolving field that we’re seeing right now is just in terms of the entire brain. You know, brain functioning, cognition. And we’re realizing that the brain itself is an organ and physical activity in some way is actually impacting that as well. So, it’s not just the physical, it’s the emotional, it’s the psychological. It’s this overall wellbeing that we like to talk about.

You mentioned the work on the brain. Is this effect that you’re talking about showing up in studies of risk for dementia and Alzheimer’s and things like that?

It absolutely is. And I think we’re still trying to completely understand the mechanisms by which this is occurring. Is it because activity is having some effect on inflammatory markers? Is it having something to do with blood circulation in the brain? Is it affecting other biomarkers that we hadn’t thought about before? But yes, absolutely. It’s affecting cognition. It’s affecting dementia. It’s affecting Alzheimer’s. And we’re finding that this is a really important thing for older adults. And I think the field is exploding at this point in this space.

Let’s get back to the physical benefits of exercise and talk about how they occur. One might think that physical activity exerts its influenced by affecting something like a risk factor, which in turn is what’s affecting health. So, you’re being physically active, it helps regulate your blood pressure and it’s the regulation of blood pressure that’s producing the overall health benefit. So, it’s exercise does X, fill in the blank, and then that creates Y benefit. But is there a direct line between the exercise and the physical health? It doesn’t go through risk factors like that. How does that work?

Yeah, I think that it somewhat depends upon what the outcome is that you’re looking for and what you’re trying to move. And it gets a little, I’ll say wonky. Because at some point there are intermediaries along the way that are probably impacted. Just for example, we’ve done studies in the field of obesity with physical activity that found that not only is the activity affecting the risk factors, the blood pressures, the insulin, the glucose. But it’s affecting like the cardiac tissue itself. It’s affecting the factors that are affecting that cardiac tissue. It’s affecting the blood vessels themselves. Now, they’re clearly intermediaries, but they’re probably not the traditional risk factors we’re thinking about. They’re probably more signaling mechanisms, mitochondrial factors, these types of things that are more physiologically based as opposed to what we would consider our traditional risk factor base. I think the thing that we’ve known now for a long time, you go back to some of the Harvard fatigue laboratory studies where they were actually trying to get performance out of individuals. How do you get people to perform at a higher performance? Basically, the equivalent of being an athlete nowadays. And what you find is that, yeah, that’s how you get people to perform at a high level. But that’s also how you get people healthy in everyday life. We really learned how if you stress the body a little bit, the body adapts and makes it stronger as you go forward.

It’s good to know that, and it doesn’t hurt to get wonky sometimes. That’s a very interesting description that you gave. You mentioned weight control. Let’s turn our attention to that for a minute. You were the lead author on a consensus statement from the American College of Sports Medicine. A very highly regarded organization, on the role of activity in body weight. Let’s talk causation. Most people appreciate the key role of diet in the genesis of weight problems, but less so the role of physical activity. How important is it?

I think it’s critically important, but I also want to be very cautious about saying that it’s more important than diet or energy intake. I don’t like to take that stand because I think there’s inputs coming from all angles here that are regulating body weight. And I think that we can get ourselves in a little bit of trouble if we say, what’s only this, or it’s only that, that it’s one thing. It’s a little bit of everything. And I think that what we’re finding a bit in our research and others as well is that there’s a variable response depending on the person. We know that if a person becomes active over six months without intentionally trying to change anything on their diet, they’re probably going to lose a couple of kilograms. Two, three kilograms, maybe a little more depending on how much they do. But there are going to be some people that lose a lot more. Some people are going to lose a lot less. The question is, why is that? And in some of our work, Kelly, we have found, and others have found this as well, is that for some people, when they become physically active, the body has this adaptation where it says, hey, wait a minute, this is great. It can kind of turn off or help to better regulate the hunger satiety signals. But for other individuals, when they start becoming more active, all of a sudden they start to become more hungry. And, in that individual, if we ignore the intake side, if we ignore the dietary component, that person could start being active, but their body weight may never move because there’s this counter regulatory mechanism for that person.

So, it’s critically important to help with regulation of body weight, but how much and how often may vary. And I think the other key factor, Kelly, is I think you’ve heard me say this before, but I’ll say it again. And that is activity can affect some of the health parameters and the outcomes we’re interested in, that weight may not affect, or diet may not affect. If we’re really thinking about a holistic outcome for patients, we’ve got to have activity as part of that discussion.

Plus, when you get diet and activity working together, I imagine you get this virtuous psychological and biological cycle. That if you’re being physically active, you feel better about yourself. And you don’t want to undermine your diet, so you stick to your diet better. That helps you be more physically active. Just a lot of things working in sync.

There’s a lot of things when they start to come together. Your body can regulate itself pretty well. It’s when we start to force other things into the system that kind of mess it up a bit. And I think the other challenge here is that I think over the years, many individuals don’t know what hunger feels like. And so, we’ve lost that sense. But being active helps to help you to counter regulate that for many individuals. So, it’s not just about the energy expenditure. It’s not just about the effect it has on weight. It’s about some of the other factors that are being affected that help to let the body get a little bit more on cruise control and let it do what it’s supposed to do.

We’ve talked a little bit there about how these two systems, the diet and physical activity, might interact psychologically. And let’s get a little more wonky and talk about the biology of it. I remember some studies, and I have a vague recollection of these because they were done a long time ago. And I thought they were done by Jean Maier’s lab and at Harvard in the sixties and seventies, where they took lab animals, which of course is a way to isolate the biology because you don’t have human psychology to worry about. And they had animals that were on a particular diet and then they either allowed them or forced them to be physically active. I forget which. And my recollection is that the animals started choosing a different mix of nutrients because they were physically active. And that mix of nutrients became a healthier profile for the animals. I’m not sure I’m remembering that right. But how are these two things linked biologically, do you think?

I think that they really link a lot biologically. And I think that we completely 100 percent don’t fully understand it all. But I think, sometimes when we think about body weight regulation, the first thing we think about is cutting the calories, and then throwing the physical activity on top of that. And I think that sometimes maybe what we need to do is feed the body and put the activity on top of it so that we have enough energy coming through the system when we talk about it. And Maier’s lab looked at this in terms of energy flux. So, if you feed the body enough and then have enough energy burn on the other side of it, that helps to regulate body weight a lot better, it appears, than someone who’s trying to always restrict their calories and add all this activity. At some point, the body’s going like, feed me. I need to eat at some point. These two things are not independent. And I think, Kelly, you know how it’s been treated for decades. You have diet and you have activity and never show these things cross paths. And the reality is that we need that cross pollinization. We need these things talking to one another because that’s how the body’s properly regulating these things.

Yeah, that strikes me as a particularly important and exciting area of research with the way these two systems come together. And you just confirmed that. I know over the years people have written a lot about how physical activity might be especially important in people maintaining weight loss. Can you tell us more about that?

Yeah. And we contribute a lot to that. We talked a lot about this, and we found, at least in secondary analyses or observational data, how important the activity is. It seems to be a very important predictor. And the question becomes, well, why? Why is that? Why is it so important? I think part of it is, you know, that as people lose weight. And you’ve been involved in many of these studies too. You lose weight and you’re cutting these calories back. You can only maintain this kinda low calorie intake for so long. And at some point in time, either you intentionally or unintentionally start to eat more calories. And these higher levels of activity, I think, help to give us some ability to kind of counter that intake. The activity becomes important that way. But also, and it takes us some time to get to that point in time. One, it’s a calorie burn. But also, if you start thinking about substrate utilization and other things, what energies are we burning, what we do know is that individuals who become more at least cardiovascularly fit, also have an improvement in their ability to utilize fat as an energy source. So, they’re going to become a bit more efficient at using fat and not always having to kind of struggle, you know, to do that. And, the other factors that really help to regulate weight, and there’s a lot of them, don’t get me wrong, we can’t talk about them all today. But you start to think about how insulin and glucose regulation might be impacting hunger satiety, but also body weight regulation, and activity we know increases insulin sensitivity. You don’t need to be dumping as much insulin into the system. I think there’s all these factors that come into play and it hits that crescendo, I’ll guess. When after you’ve done it for a period of time and these adaptations have happened after about 3 to 6 months, you’ll start to get many of these adaptations occurring.

People are going to get excited when we’re talking about substrate utilization. But let’s go into this a little bit more. And actually, it was the next thing I was going to ask you anyway. Whether people, when they’re burning calories, I mean, they’re losing weight, are they burning fat or protein or, what’s the body doing is a really interesting issue. And I know that’s especially important in the context of the new weight loss drugs. So, let’s talk about that. We’ve done several podcasts on the new generation of the GLP drugs like Ozempic and Wegovy and Mounjaro and Zepbound. So why is physical activity especially important when people are using those drugs in particular?

Yeah, so much of what we know about activity within the context of those medications is a bit hypothetical. A bit hypothesis driven. A bit this seems like the best practice because there have really been virtually zero studies, we keep looking at this, that have been published that have been appropriately well designed, appropriately powered kinds of studies. The one study that has been out there had people lose a lot of weight on basically a low energy diet and then added activity and the medication after they’ve already lost a lot of weight. It’s really not the way these medications are really being used. And so, in our consensus paper from the American College of Sports Medicine, we talked about what we don’t know as much as what we do know. And I think that activity becomes critically important in the context of these medications because beyond what it does for body weight, true body weight, the medications are taking care of helping people to lose weight. But as we hear about these weight loss medications, there is some concern about the loss of potentially lean mass. We don’t know if it’s muscle or not, but there’s a potential that some of that is muscle.

I just heard some data over the weekend about some of the newer medications that are being looked at in phase two and three trials, where there’s some concern about bone loss at this point as well. So, you start to think about that and you say what could you do to maybe not completely counter it, but to blunt the loss. And we know that activity affects all those things in very positive ways. The challenge you run into though, Kelly, is activity affects those things in very positive ways when there’s adequate nutrients coming in. But if all the nutrients are coming in are being used for energy, there’s very little to have as a building block.

So, we have to be careful about saying that exercise is going to prevent loss of muscle, prevent loss of lean, prevent loss of bone. It may help to counter regulate that, but I think that what’s more important is whatever muscle and lean tissue and bone tissue you have left let’s make it as healthy as it possibly could be. Because as you and I both know, individuals without obesity actually overall have less muscle mass than individuals with obesity. The difference is in their quality of their muscle. And so, let’s make the muscle that is retained high quality as opposed to focusing so much on the volume

It sounds like the combination of really being vigilant to protein intake and physical activity is a pretty good way to help counteract some of the negative effects of the drugs on the potential loss of muscle mass.

I think that there’s a chance that it could help. But if worst case scenario, we don’t know if it’s completely countering that, but it might blunt it. But the bottom line though is that even if it’s not blunting it, even if it’s not stopping it you’re going to make the muscle stronger. You’re going to make the muscle more functional, make the muscle more efficient with the muscle you have left with activity. And an example of that Kelly is, probably 30 years or so ago now, we published some papers on the very low-calorie diets, the five to 800 calorie a day diets. And we added resistance training, cardio training, or the combination to those diets. And, with a 20, 30-kilogram weight loss over three to six months, we saw losses of lean mass even with the exercise training. But the people who weight trained got stronger. The people who did cardio training got more fit. The people that did both had both effects. You still get the effect of the activity without focusing so much on the mass, but focusing on what I’ll call the quality.

I had this image in my mind while you were talking, if muscles had a face, they’d be smiling at you if you’re physically active, because you’re helping make them stronger and more vital. And, it just so many good things happen, don’t they?

That’s it. I think that’s exactly what I think the message should be because we’re not trying to train athletes here. We’re trying to train everyday humans and their everyday walk of life. So, how can we focus on making them the healthiest and most fit and most functional that they can be? And I think that’s a lot different than trying to say, we’re going to send you to the gym five days a week and really hammer you to try to preserve this. Most people can’t do it and won’t do it. What can we get from this? And I think this quality issue is really where we should be focusing our effort.

Let’s get a little bit into the nuts and bolts, toward the end of this conversation about what type of exercise people might think about doing. We’re bombarded by information: low versus medium versus high intensity. For how long should you do it a day? How many steps should you get? Strength training versus aerobic exercise? You just mentioned that. And of course, how to get it and stay motivated. So how do you respond to the question? What do I do?

Yeah, a very difficult question. And I think part of that comes from just the media is not understanding so they look for a good story. But part of it also comes from within the exercise community. Similar to what you see in the nutrition community, what’s the optimal diet for someone, right? And so, you have people who are advocating for one type of activity versus another activity. And as I go out and I talk about this, I think this is critically important, Kelly. There’s not one perfect exercise that will give you all the perfect health benefits. If you want to strengthen the muscle, you need to overload it with resistance. If you want to make the cardiovascular system strong, you need to stress it with some type of cardio activities. If you want the muscles to become pliable and the tendons and ligaments to become pliable to prevent injury and so on, you’ve got to do stretching, Yoga, tai chi type of activities, right? And you can go on and on and on. And in fact, if you want the brain to function, if you want the cognitive effects, you need to do things that make the body think a little bit and tie the brain to the movement that you’re doing. Right? So, it has to be like a mindful type of movement, maybe a yoga or something like that. There’s not one perfect activity, but I think that a little bit of all those activities is probably better than any one of them by themselves. That’s the way I think about it. Now that’s hard for people. Also, I think that for people that are starting out who probably have had bad experiences with exercise, bringing back to physical education class possibly, right? Get up and move more. If you can get up and move more, that’s the gateway. Right? Get up and just start moving around more. If you can’t get up and move more, there are things you can do. And if you’re wheelchair bound or have mobility limitations, there are things that can be done in a seated position and so on. It’s about getting started. The, the hardest part is taking that first step. Right? The hardest part is putting on those walking shoes and getting out the door. Once you’re out there, people usually enjoy it. And I’ll just give you an example. Kelly of when we did our bouts and you’re familiar with our study where we did the 10-minute bout study where we asked people just to do 10 minutes. We found very quickly that individuals who started doing small 10-minute bouts and we’re doing well, were turning those bouts into 12-minute bouts, 14-minute bouts, 15-minute bouts. So, it’s about getting that first step. Don’t think about this being this whole complex thing. Let’s get started and build on it to a lifestyle of activity.

And if people are in search of a trustworthy place to look for information on physical activity, where would you suggest they go?

First, if they’re looking for a website type of thing, I would point them to the American College of Sports Medicine. There’s a program out there called exercises. Medicine has great resources, but also if they’re looking for good advice, and it’s, a lot of people can give good advice, but the American College of Sports Medicine has the premier certification in this space. Individuals who are getting American College Sports Medicine Certification, whether it be a personal trainer or clinical exercise physiologist, are going to be, in my view, the people who have the kind of the right perspective to try to help individuals with variety of different disease states.

That’s very helpful to know. Let me peer ahead into the future a little bit and ask you, where do you see your field going? What will the future bring, you think?

There’s a big study going on called the molecular transducers of physical activity. It’s they. I call it the motor pack study. We were involved in that for a while, and that’s to try to create a molecular map of how activity actually affects the body. Kind of like where we started today. We’re learning a lot about this. And I think that what we’re going to find in, and not just in that study, but across the board is this idea that again, there’s not one perfect activity. But that the body responds to activity, depending on what it is that you’re asking it to do. And I think that the holy grail, Kelly, is no longer what activity is should I do? I think the holy grail goes back to maybe where your roots were and my roots were, and that is how can we help individuals to initiate, engage, and sustain? I think it’s about the intervention and translation of these findings. And that’s the holy grail for our field because we know activity is good for us. It’s about how do we get individuals to understand, engage, sustain, and overcome the barriers that they face. I think that’s where the field has to go.