in: Health, Health & Fitness, Podcast

• Last updated: September 30, 2021

Podcast #552: How to Optimize Your Metabolism

If you struggle to lose weight, you may blame an inherently slow metabolism. But is your metabolism really to blame, and can you increase it in order to burn more fat?

Today we tackle these questions and more with Dr. John Berardi, who earned a PhD in exercise physiology and nutrient biochemistry, and is a writer, athlete, coach, and professor, as well as the co-founder of Precision Nutrition and the founder of the Change Maker Academy. John and I begin our discussion with what metabolism is, the components that make it up, how much each element contributes to your body’s energy expenditures, and which can be controlled. We then get into whether or not it’s true that some people have an inherently slow or fast metabolism, and how diet and exercise influences your metabolism, including whether or not dieting itself can slow your metabolism down, and why you might want to consider wearing a weight vest around once you lose body fat. We then discuss how intermittent fasting can increase your metabolic flexibility, whether there are certain foods that boost your metabolic rate, and the best exercise routine for optimizing your metabolism. We also also talk about how stress and sleep effect your metabolic health. We end our conversation with John’s best tips for maintaining optimal metabolic health and losing weight in general.

Show Highlights

  • What is metabolism?
  • What’s the most “expensive” energy expenditure of our day?
  • What is NEAT? What role does it play with your metabolism?
  • How much of your energy is spent on exercise and physical activity?
  • What does science say about “fast” and “slow” metabolism?
  • How can an efficient metabolism cause weight gain?
  • How meal-skipping affects people differently 
  • Diet, weight loss, and metabolism 
  • How easy it is to accumulate extra calories (and how not to obliterate your dieting) 
  • How to nail your exercise to optimize your metabolism 
  • Does increased muscle mass help your metabolism in a noticeable way?
  • The role of stress in your metabolism 
  • Why a sleep deficit torpedos your health in all aspects 
  • Does metabolism really slow with age? Or are other lifestyle factors at play?

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Precision Nutrition

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Read the Transcript

Brett McKay: Brett McKay here and welcome to another edition of the Art of Manliness podcast. If you struggle to lose weight, you may blame an inherently slow metabolism. But is your metabolism really to blame, and can you increase it in order to burn more fat? Today, we tackle these questions and more with Dr. John Berardi, who earned a PHD in exercise physiology and nutrient biochemistry. He’s a writer, athlete, coach, and professor, as well as the co-founder of Precision Nutrition, and the founder of the Change Maker academy. John and I began our discussion with what metabolism is, the components that make it up, and how much each element contributes to your body’s energy expenditures, and which can be controlled.

We then get into whether or not it’s true that some people have an inherently slow or fast metabolism, and how diet and exercise influences your metabolism, including whether or not dieting itself can slow your metabolism down, and why you might want to consider wearing a weight vest around once you lose some body fat. We then discuss how intermittent fasting can increase your metabolic flexibility, whether there are certain foods that can boost your metabolic rate, and the best exercise routine for optimizing your metabolism. We also talk about how stress and sleep affect your metabolic health, and we end our conversation with John’s best tips for maintaining optimal metabolic health, and losing weight in general.

After the show’s over, check out our show notes at

All right, John Berardi, welcome back to the show.

John Berardi: Thanks for having me back, I really appreciate it. I always enjoy coming on. Before you and I started doing podcasts or articles together, or whatever, I was a huge fan of the site, and of the podcast, so it’s really an honor to chat with you man.

Brett McKay: Well, thanks so much. So you are a nutrition coach, you have your PHD in exercise physiology and nutrition biochemistry.

John Berardi: Yep.

Brett McKay: We had you on the show a couple years ago, talked about the science of intermittent fasting, that’s episode number 328 for those who want to check that out. And today, I wanted to bring you back on the show to discuss an aspect of nutrition and health that I think people have heard the word and the concept a lot, but I don’t think they fully understand it, and that’s metabolism. It’s a word that we throw around a lot, “Hey, I got to speed up my metabolism. I can’t lose weight, because I have a slow metabolism.” But I would like to unpack what metabolism is, so people have a really good understanding that it’s more than just about losing weight, there’s other things that go on with it.

So let’s talk, let’s start with the very basic, what is metabolism?

John Berardi: Yeah it’s great, let’s start there, yeah. Basically, it’s the sum total of all the cellular activity that goes on in your body. So that’s kind of a vague answer, but generally, in this miracle of life, us being alive is really a series of sort of communications, between different cells and of our body, and metabolism is all that activity that’s going on at any point in time. And that’s the description, if you will, but when we think about measuring it, for example, there’s an equation that we can use to figure out how much activity’s happening at any point in time. We usually call that total daily energy expenditure, so the sum total of all our metabolism costs energy, keeping a human alive costs energy.

And so the components that total up to our total daily energy expenditure, resting metabolic rate, so that’s just the functions that keep us alive. That’s our activity levels, and a lot of times people think about that as exercise, but it’s any movement at all. So there’s actually a component of activity called NEAT, Non Exercise Activity Thermogenesis, and this is kind of a fascinating one, where it’s kind of genetically determined. So some people tend to move around, it’s been called fidgeting before, more than others when they’re not purposefully exercising. So this is actually another important component of the activity, sort of part of the equation.

And then, the one I’ve always found that’s really interesting, that we parse out, is the thermic effect of feeding. So eating itself, and the mechanical process of eating, plus the chemical process of digesting that food, breaking it down, and transferring it to our cells, is also another component, so that’s called the thermic effect of food. So when we think about metabolism, it’s all this wonderful activity that’s happening. When we go to measure it, we can measure it as total daily energy expenditure, how much energy we burn in a day, and then to think about what contributes to that, it’s our resting metabolic rate, just the functions that keep us alive, plus all the movement we do in a day, anything beyond laying still, and then the thermic effect of feeding.

So those three things add up to total daily energy expenditure, which represents a measure of our metabolism.

Brett McKay: All right, so metabolism is everything our bodies do to keep us alive, to function, to think, talk, breathe, move, et cetera. All of which expends energy. So metabolism is everything that creates life, that we tend to narrowly associate it with weight gain and loss, and we’ll try to give people a better understanding of that aspect of metabolism today in our conversation. You mentioned several factors which contribute to our metabolism, which are resting metabolic rate, NEAT, or non-intentional exercise like fidgeting, and then there’s thermogenesis, when we eat and our bodies convert to energy, and exercise.

Is there a pie chart of how much each energy expenditure makes up our metabolism?

John Berardi: Yeah, there is actually, and most people are actually fascinated by the breakdown. The most expensive part of the daily energy expenditure that we use up comes from our resting metabolic rate, it’s not from our activity, it’s from just the functions of keeping us alive. Now, if you’re not very physically active, about 75% of your total daily energy expenditure comes from just the resting metabolic rate, keeping you alive. About 15% will come from activity, and about 10% from the thermic effect of feeding.

So as you can see, most of this is just keeping us alive. Now that shifts a bit, if you are highly physically active you may end up with 60% of your total daily energy expenditure coming from resting metabolic rate, 30% from activity, including NEAT, and 10% from the thermic effect of feeding. So you can see the bulk of the calories that we use in a day is just resting metabolic rate keeping us alive stuff.

But you can also see that exercise can make an important difference to that. It can shift it from 15% of your energy burned in a day to 30%. And obviously we’re just talking about percentages, so this would be a pie chart. You have to realize that when you start exercising more, the total pie gets bigger. So the amount of energy you burn in a day is much larger. So your resting metabolic rate may not change at all, but it goes from 75% of the pie to 60% because the pie grew, if that makes sense.

Brett McKay: Yeah that makes sense.

So let’s talk about this idea of fast metabolism, and slow metabolism. I mean when people hear that the laymen thinks, “Well, if I have a fast metabolism my body uses a lot of energy, if I have a slow one it uses less.” What does that mean from a scientific point of view? When you hear fast metabolism, what do you think?

John Berardi: Yeah, I mean the thing is there are individual differences, for sure. You only need to look around the world and see there are some people who seem like they can eat all they want with no regard for caloric intake, and not exercise at all, and their body appears skinny, quote unquote.

And others who really seem to watch to what they eat, and they do purposeful exercise, and they may have a heavier body weight, or carry more body fat. So there are some factors that affect resting metabolic rate, because that’s what we’re thinking about when we think about, hey, let’s say exercise was equal. Two people have different bodies, well then their metabolisms might be different based on their resting metabolic rate. But what we often find is that there are subtle things that actually shift the rest of their lifestyle, that make it less about this sort of magical, like a fairy waved a metabolism wand over them and made them a fast metabolism or a slow metabolism. So for example, a lot of people who think they have a very fast metabolism actually don’t understand the impact of NEAT, that they are fidgeters. So they may burn an extra 10, 15% calories each day just fidgeting around.

So they may not quote unquote go to the gym, whereas someone with low NEAT, who does go to the gym, could end up burning fewer calories in the day, even though they’re like, “What the heck, I go to the gym for an hour every day.” So oftentimes, there isn’t any magical disappearance of calories, or appearance of calories. It’s this simple equation. Resting metabolic rate plus activity, either purposeful or unintentional, and thermic effect of feeding. So someone has a quote unquote slow metabolism, you just have to look at the equation and say, “Well, what’s slow?”

Is it the thermic effect of feeding? Probably not, because that’s pretty standard between people. Is it their resting metabolic rate? Probably not, that could be plus or minus, but a resting metabolic rate’s largely determined by body size. So if you’re a bigger person, it’ll be higher, and if you’re a smaller person, it’ll be lower, and that makes total sense because if you’re bigger you have more cellular function to account for and then your size also influences the activity you burn, too, because if you’re a bigger person it’s harder to carry that weight around when you do move.

It’s often why, when people lose weight at let’s say a certain caloric deficit, like they’re following a quote unquote diet, or eating fewer calories, and they start to lose weight, and then that weight loss plateaus, and they’re like “I don’t understand, I’m still at the same deficit, I’m even exercising a bit more.” Well, they’ve lost weight, so it’s less expensive to carry around the current weight they are.

I actually have a friend, I was just at an event recently, and a strategy he’s been playing around with is putting a weight vest on people. They live most of their waking hours with a lightweight vest on that accounts for the weight that they’ve lost. Let’s say they start at 200 pounds, and they start exercising a bit more, and eating a bit less and they drop down to 190 pounds. Well then he would put a 10 pound weight vest on them, so they’re still carrying around 200 pounds.

Now, I’m not saying this is for everyone. But what he’s found there is that they don’t have to keep lowering their calorie intake, or increasing their exercise. They can continue to lose at a similar rate, without pushing the exercise harder, or eating less, by accounting for that body weight, which seems like such a simple thing, but it makes such a huge difference, and it frustrates a lot of weight loss efforts.

Brett McKay: Yeah, we’ll talk about the role of dieting, and how it can slow down or speed up your metabolism. But I think another interesting concept that you’ve written about in different places, is this idea about understanding how our metabolism, or our body, wants to be efficient. Now when we hear efficient, typically we think, “Oh, efficiency’s great.” Right, you want a factory to be efficient. We want our lives to be efficient, because it means we’re getting a lot of stuff done, nothing’s going to waste. But how can an efficient metabolism cause weight gain?

John Berardi: Yeah, well in the sense of metabolism, like we talked about earlier, the body wants to make life lest costly, right. So we don’t often get more efficient at let’s say our resting metabolic rate, but it often comes to play with exercise, for example. Let’s say you’re going to start getting in shape and you don’t have an exercise routine, and you’re gonna run one mile.

The first few times you do that one mile, you’ll be inefficient. Your body hasn’t up-regulated the enzymes that are necessary for rapid energy production. Your technique is probably poor. You’ll probably be heavier, so you’ll use more energy just carrying that extra load around. And as you do that one mile over and over and over again, your body finds ways to make it easier, to make it less challenging. So you may lose a little bit of weight, your enzymatic systems will up-regulate, your technique will get better, especially as you drill technique over and over. In that case, if you continued to run that mile, the calorie cost will be less, even though you’ll be going faster, and that’s because you’ve gotten efficient.

Now, that’s good for performance, right, but it’s not that great for calorie burn, unless as you get more efficient, you increase the intensity. So you make it just as hard for the body as that one mile was. So you can either go two miles, or you can go one mile markedly faster by pushing the intensity. But efficiency in this case, as per your question, would be if I go out and run a seven minute mile today, and I’m still doing that three months from now, that seven minute mile is going to be markedly less effective, because I’ve gotten more efficient.

So as you say, efficiency we usually think of as good, and it is good in this case, from the body’s energy use perspective. However, this is where our bodies don’t share our same goals. If you want it to lose weight, you want it to squander energy.

Brett McKay: So talking about this inefficiency with nutrients, so basically in order to lose weight, we have to be inefficient, which means we have to spend more energy than we’re bringing in. So I’m trying to think of this with body fat for example. Our body stores fat, I imagine our body’s like, “You’re not going to touch that fat.” So it makes it really hard, our body does something once we start reducing caloric intake, to say, “No, I’m not giving up this body fat.” And so it makes it… you have to work more to get to it. And so it’s sort of putting up inefficiencies to protect… it’d rather use dietary body fat, I guess, is what I’m saying, than your stored body fat to power itself.

John Berardi: Well, it actually does depend on the situation. I did a pretty deep dive into literature on this, and it seems like, if given the choice, and it’s hard to control for, the body would prefer to burn what’s stored on it before it burns what’s coming in from a dietary perspective. It’s why intermittent fasting, for example, although it takes a little bit of time to adapt to, it’s why it ends up working fairly well. Because most of us have loads of meals stored on our body that the body actually wants to eat, so if you go an extended window without eating, so 16 hours or whatever intermittent fasting protocol you’re using, the body will gladly eat that stored food up.

The challenge is, and this is what you’re bringing up, is that at first when we train the body to eat the food that’s coming in, so we eat on a very regular cadence, and the body’s used to that, it will actually become what’s called metabolically inflexible, and this the more interesting concept than fast or slow metabolism. To me, it’s metabolic flexibility. The idea that I could not eat for an entire day, let’s say, and instead of getting low blood sugar, and feeling really low energy, because my body hasn’t yet figured out, or up-regulated the pathways to eat the food that’s already on me, I’ll actually do that.

One of the best ways to actually teach metabolic flexibility to the body is systematically, over time, doing extended fasts. So let’s say you normally only fast for 10 hours with an overnight sleep, well then you might push it to 11 or 12, and then 13 or 14, and then 15 or 16, not as a life project, but as a training program. A short term training program for metabolic flexibility. So your body starts to learn, “Oh when I don’t get external food coming in my mouth, I can just up-regulate certain hormones, and certain enzymes, so I can just eat the food that’s already on me.”

So, like we talked about last time on the podcast, intermittent fasting does all these things, some good, some not so good depending on the person and the goal and the conditions, but one of the things that I think it can do, not as a lifestyle choice but just as a training program, it can help with the metabolic flexibility thing, and teach the body, “Hey if carbs are coming in I can use those. If fats are coming in, I can use those. If nothings coming in, I’ve got loads of carbs and fats on my body already, I can just use those.” And so one of the things I often hear when people think about let’s say skipping breakfast is, “Oh, I get way to hypoglycemic and I feel terrible.” And that makes sense.

If you are on a program of eating frequently, your body doesn’t know how to tap into the stored food that’s already on it. So, we train it. And then it becomes a choice, not necessarily that I want everyone to do that. But it becomes an option, you could skip breakfast, or not.

Brett McKay: Well let’s talk about diet and metabolism and weight loss, because when someone needs to lose weight the first thing they think is well I got to reduce the amount of food I eat, and as you mentioned earlier that’ll work, you’ll lose weight. But then you’ll reach a point where it no longer works. So what’s going on in our body, is it because our body is smaller, it requires less calories, so it’s not burning… you’re no longer in a calorie deficit?

John Berardi: Yeah, well that’s it. Most people think it’s that dieting itself slows down the metabolism, so when I eat less food I burn fewer calories, and that’s true for some people, and not true for others. But even for the people it’s true for, it’s probably largely irrelevant.

I mean, there’s been some studies showing that there’s folks with what’s called sort of a thrifty, or spend-thrift metabolisms. So the first study I saw on this was where they took a big group of individuals and they overfed them. So they put them on a weight gain diet. And I think it was 1,000 extra calories a day. So that would accumulate calories pretty quick, and you’d gain weight pretty fast. And so what they found at the end of this 12 week period of overfeeding, was that there was a group of people that gained almost no weight, and there was group of people that gained like 35 pounds.

And so when they looked at them, they had to sort of look at matching on body size, and reported caloric intake, and activity levels, they were like, “It doesn’t make sense why this group would gain no weight, I mean we overfed them a lot of calories over the course of this protocol.” And what they concluded was that, and subsequent studies sort of back this up, was there was a type of metabolism that was called spend-thrift. So as these people ate more, they found ways to burn more calories in the day. So, they may have done more purposeful activity, but most of it probably came from NEAT, this non-intentional activity.

So fidgeting, walking around, I often think about this, you ever seen people who take a phone call and they just pace while they’re talking on the phone?

Brett McKay: Right.

John Berardi: Well that’s an example of NEAT, right. They’re not like, “I’m going to exercise, now.” Right? But they walk five miles while they do an hour long phone conversation, where others may be sitting down for that whole conversation, and that matters in terms of the accumulation of energy expenditure. So that’s what these sort of spend-thrift people do, where the thrifty people didn’t up-regulate at all.

So the same thing happens in the case of weight loss. There are some people, when they lower their calorie intake, their calorie burn stays the same when adjusted for their new body weight. There’s others that, when they lower their energy intake, they burn fewer calories when adjusted for activity levels. But, as you said, and as we talked about earlier, most of the effect when you’re quote unquote dieting happens from weight loss. You lose weight and you burn fewer calories just moving around. So every step you take costs less because of the weight loss. So it has very little to do with dieting slowing down our metabolism, although for some people that might be a small difference. It’s mostly the weight loss that sort of makes it more efficient to move around.

And that’s why that weighted vest thing becomes so interesting for some people, right. If that weight loss is what causes this enhanced difficulty with subsequent weight loss, then replacing that body weight should help.

Brett McKay: Well, and apart from putting on weight vest, the other option is once you’ve reached that plateau, you just have to reach calories a bit more in order to keep . . .

John Berardi: Yeah so either exercise a bit more, or reduce calories a bit more, yes.

Brett McKay: But there’s only so far you can go with that, right. You can only drive down the amount of calories you consume so much before you’re not eating anything.

John Berardi: Yeah, that’s right. Or what happens much more frequently is that your hunger signals get so intense that it’s impossible to sustain that calorie deficit. There are competitive body builders, for example, who put themselves on a 12 or 16-week diet, and they have tremendous discipline, they lots of practice doing this, they’ve done it time and time again. And so during that time, they will continually reduce calorie intake until maybe a 200 pound guy is eating 1200 calories a day, and exercising daily.

And so they’ll do it. They’ll do the exact thing that we just talked about, but it’s impossible to sustain, and most of these people will gain thirty pounds in the next two weeks after their contest is over, because hunger signals go through the roof, it’s just impossible to maintain this kind of deficit over time as a real human being, living in a real world full of food options. So as you say it’s just not reasonable to continue to drive calorie reductions after a certain point

And people are always looking for what that number is. It’s impossible to come up with that number, the research hasn’t come up with a number. People have, again, different metabolic rates, they have different body sizes, they have different levels of physical activity. There’s no number we can say below 1,000 calories is when it gets unhealthy, or dangerous, or whatever. Those numbers are all made up.

Really, I think we have to think pragmatically and say, “Below the level of caloric deficit, or below a certain level for you, personally, you just will be so hungry all the time that you’re going to make up calories somehow.” And I remember wrote an article a while back about this. I was in an event in Arizona and I went out for a meal at the Cheesecake Factory, and I remember looking at the menu, because they had just started to include caloric values on the menu, and I was like, “Wow, there’s a lot of calories in this cheesecake right.” So I ordered a meal off their healthy menu, so it had the little lettuce leaf next to it, or whatever, and so it was like a light pasta with vegetables and chicken. And then I had a piece of cheesecake for dessert.

So this wasn’t an extravagant meal, it was a healthy offering at Cheesecake Factory, plus a piece of cheesecake. And then they hadn’t listed the cheesecake calories, so when I went home I looked it up online, and I realized I had eaten something like 3,800 calories in that meal.

Brett McKay: Wow.

John Berardi: I know. So I was like, “Okay.” Imagine that you were wanting to lose weight, and you’re quote unquote eating at an energy deficit. And so over the course of six days of the week, so let’s say you went out for Cheesecake Factory on Sunday. So the previous six days you were in a 500 calorie a day deficit, which should accumulate good weight loss over time. That would be 3,000 calorie deficit. And then on Sunday, you’re like, “You know what, I’m not going to have a cheat day, I’m just going to have one cheat meal, and I’ll choose something healthy, and just have that one piece of cheesecake.”

That one meal would obliterate your entire week of calorie deficit. It’s sad and disheartening, but it actually shows the reality of how easy it is to accumulate extra calories, even when you’ve… let’s say you eat three meals a day, over seven days, that’s 21 meals. 20 out of 21 meals were great. That one meal obliterated the rest. That’s how sensitive this system is. But, I mean there’s some great ways to not obliterate it, and to make thoughtful choices in a way that you can see consistent weight loss.

Brett McKay: I think understanding that as you lose weight, your body requires less calories to function can explain the sort of the phenomenon of yo-yo dieting. People will say they lose 15 pounds, “Well, I lost 15 pounds. I can go back and eat good food again.” But it’s like no, you can’t, because your body requires less calories because it’s smaller, and so if you go back to eating like how you did when you weighed 15 pounds heavier, you’re going to gain 15 pounds again.

John Berardi: That’s right, and maybe even a little bit extra, because if you lost the weight by being pretty restrictive, then rarely do people go back to eating normal after they’ve been on a calorie deficit. What they do is they go back to eating normal, plus 10 or 20% and then if you track people’s intake, that’s exactly what happens. They eat at 80% of normal for a while, they lose the 15 pounds, and then when they quote unquote go back to normal, there’s an overcompensation, and so that’s why they end up gaining back the 15, plus a little bit of extra.

Like you said, there’s less metabolic costs, and now they’re eating well over their needs, even higher than they would’ve been eating before. And so this is why yo-yo dieting happens, and it’s why the cliché exists, this has to become some kind of set of lifestyle choices, rather than a short term weight manipulation strategy.

Brett McKay: Right, so instead of thinking diet, think of how am I going to eat to maintain the weight I want to keep, or whatever.

John Berardi: Yeah, and the thing I often say about this, especially to people new to maybe trying to manipulate their body, or improve their health, is that often people they overestimate how hard it’s going to be, and they under estimate how long it’s going to take. So this idea of making smarter eating and exercise decisions as a lifestyle choice, it seems in your mind, when you don’t know what the strategies are yet, like it’s going to be really hard, but it’s actually not. There’s just small interventions that you can do. It’s just going to take a long period of time, and you have to be consistent with those.

Brett McKay: And you mentioned instead of letting that cheesecake factory meal ruin a week worth of thing, how can you still enjoy having food, like say a cheesecake, but not let it completely derail whatever progress you’ve made?

John Berardi: Well, I think, as we start thinking about the different factors that can contribute to let’s say sort of weight loss, and improvements of health, we have to look at this combination of exercise, nutrition, sleep, and stress management. These four things all have to be accounted for, or else one or more of them is going to sabotage the work on the other.

So, one way to not have cheesecake quote unquote sabotage your diet for the week, is that you have enough exercise caloric expenditure over the course of the week that it’s not a problem. And if you do have one week that you’re in calorie maintenance, let’s say, because you ate cheesecake, it’s okay because the next week you’ll be in a deficit.

So, usually I like to really build out someone’s thinking around this by looking at the specific strategies around exercise, nutrition, sleep, and stress management, and we can get into them when you want, but that can help contribute to this in the long run, so that a piece of cheesecake will be irrelevant.

Brett McKay: Gotcha. Well let’s talk about exercise, and its role in metabolism. So there’s resting metabolic rate, nothing really you can do to change that. There’s the NEAT. But we can manage, or have control over our exercise. So are there types of exercise that are really good at revving up our metabolism, causing us to expend more energy?

John Berardi: Yeah, I mean my favorite recommendation here is sort of a mixed modal exercise, and it’s kind of a technical industry term but it basically means each week you should do some strength training, so some weights. Whether it’s with body weight, or whether it’s with external load’s irrelevant. You should do some kind of interval training. So people have called it HIT, or High Intensity Interval Training, but we don’t have to use the conventional methods of doing that. I mean this could be sprints, go out on the road sprint one mailbox to the next, walk the next mailbox, sprint the next one.

You could do all of it. It could be on a rowing machine, it could be with a kettle bell. There’s all kinds of ways of doing high intensity exercise. And then the third would be a low intensity mode for an aerobic type of exercise, and it could be even less than what you’re thinking of as aerobic right now. It could be just going for a walk a few nights a week. So the idea would be that nearly every day, you’re doing some kind of activity. That doesn’t mean going to the gym, it could just be a walk outside.

But over the course of a week, or two even, you will have mixed modes. So the strength training will help with building strength, confidence, physical capacity, muscle mass, and it’ll burn some calories. The high intensity interval training will create a different set of compensations in the body, all really, really positive, but will also burn some calories during the activity, and will cause a small but not insignificant increase in energy expenditure over the next few hours, after the activity.

And then your sort of low intensity sort of walks or bike rides, or those kind of things will help accumulate, again, more physical capacities. But one of the other things that I like about this is that it creates what we call sort of parasympathetic to sympathetic balance. If all your activity is very high intensity, it engages your sympathetic nervous system, which is kind of like your fight or flight nervous system. It produces a lot of epinephrine and norepinephrine, and too much of that creates too much stress in the body.

So that’s not to say do less of that kind of activity, it’s to say balance it with parasympathetic activity, which is low intensity, stuff that gets your heart rate going but not super hard, it doesn’t cause muscle damage. So if you’re thinking about, “Okay, I want to get in shape.” Or lose weight, or whatever the case may be, I’m going to start exercising. The direction you need to go is, I have to find a way to get these three things in, and they have all kinds of different benefits, but they all work together to create this effect that I’m looking for.

And part of it, also, isn’t just “I need to burn calories.” It’s also these physical capacities, but also body remodeling. Most people, if they lost 20 pounds, but had the same shape that they have right now, would not be happy with that transformation. So what they actually want is a body remodeling. They want some of the fat around their waist, and other areas, to reduce and they want some of the lean, in let’s say their shoulders, or their things, or whatever, to increase.

And that’s a remodeling process that can only happen with mixed modal exercise, so that’s how we build it out. And again, depending on your preferences, that mix can be different. I prefer strength training, personally, so I do more of that than the others, but I still include the others. If walking is what you prefer, do more of that, and then just include one of each of the others in a week, so we can work with preferences, for sure.

Brett McKay: Well, let’s talk about strength training. Strength training, one thing it does, it helps increase muscle mass. Is there anything to the idea that increased muscle mass makes you more metabolically active, or you expend more energy?

John Berardi: There’s a whole bunch of things. If we ask certain questions, we’ll get answers to them. Whether those answers matter or not is irrelevant. Or, whether those answers matter or not is important. So this is one of those examples. Gaining muscle mass increases metabolic rate is true. But it just increases it to such a small extent that it may not be relevant.

There’s another thing that people often ask. Foods. Are there foods that speed up the metabolism? Yes, there are. Protein versus carbs and fats increases metabolic total daily energy expenditure, chili pepper, spicy foods do, caffeine containing foods, cacao, they all do, but they’re probably not worth talking about, because the effect of exercise, proper calorie balance in a week, sleep and stress management are so big compared to these minute things. It would be like dropping one drop of red dye into a huge lake.

Does the red dye, dye the lake red? Well, it adds red to the lake, but it doesn’t dye it the lake red. Increased muscle mass, chili peppers, caffeine containing foods, do they speed up the metabolism? Yes, but at the same magnitude of one drop of red dye into a big lake.

Brett McKay: Okay so that’s good to know, so don’t obsess about those little minutiae. Just eat right, don’t overeat if you’re trying to lose weight or maintain weight, and make sure you mix up your exercise so you hit all those modalities. And be consistent with it, and if you do those things you’re going to be in pretty good shape.

John Berardi: Yeah, completely.

Brett McKay: Well, let’s talk about the role of stress, that it plays in our metabolism. So what role does stress play in our metabolism?

John Berardi: I mean, it’s really interesting because stress has such important negative effects on health and weight management, but it doesn’t really have much impact on, let’s say, total daily energy expenditure. So it’s probably not going to shift our energy expenditure too much, but when we’re under psychological or physiological stress, so it could be too much exercise, too little food, it could be emotional stress at work, or in a relationship. It increases our cortisol, which is our stress hormone, which breaks down parts of the body.

It increases our sympathetic nervous system activation, our epinephrine release. So what we find is that people under long-term stress have known outcomes. They gain more central weight, which is sort of where you gain fat around your organs, and that’s the most unhealthy kind of fat to have. It causes an insulin resistance, and increased blood pressure, and those are the very physical changes. It also causes cravings, I mean the research shows over and over again, when people are under psychological stress, they end up eating more foods that we consider foods that you should reduce.

It causes problems with sleep, and then there’s the social outcomes, like social withdrawal, and depression, and there’s immune and hormonal changes. So one of the great books on the subject is called Why Zebras Don’t Get Ulcers, and for people who’re really interested in this, that book sort of covers it all. And it’s really a fascinating trip through the often unexpected effects of stress on all the different systems of the body.

So while it’s not a necessarily like a potent energy expenditure disruptor, it can disrupt metabolic health through all the mechanisms that I just talked about.

Brett McKay: Yeah, I had this weird experience that my recent training cycle, I think it might have been stress related. I’d love to get your input on this, so in July I went on vacation in Vermont. It as a working vacation but I did plenty of hiking out in the woods, I was swimming in cold creeks, it was fantastic. I get back in August, and I start a new cycle and it was just going great, and I had to keep bumping up my calories because I was just super hungry at night.

So every week, I kept bumping them up, and going but still hungry, and it got to the point where I was consuming 4,100 calories a day and I wasn’t gaining weight, I was just feeling great, everything was awesome. And then middle of September I hit this patch with work where things just got really stressful, and I maintained my caloric intake, maintained the same activity level, but I just wasn’t sleeping well, I was not feeling good, stressed. And then a week later, two weeks later, I started noticing I was getting pudgier, and my face was getting fatter, my waist was getting bigger, so I had to start reducing calories to offset.

I don’t know if it was the stress, but it was just a weird thing to see happen where I could consume a ton of calories and not gain weight, but then it reached a point where I got stressed, and then that stopped working and I had to adjust.

John Berardi: And yeah, the important thing is then we unpack. Were you gaining weight, or was your body comp shifting, right? And I mean the explanation for this is fairly easy, unless it’s something uncommon, like as stress accumulates, we produce more cortisol, and cortisol actually can cause water retention, so it’s one of the known effects. An over-production of cortisol is called Cushing Syndrome, and it’s described by this very round, what people have called sort of moon-face, which is just this tremendous, abnormal water retention. So again, sometimes it’s really hard in the course of an individual, personal life to figure out what’s happening.

You start to feel and look pudgy, and you’re like, “Oh, I’m gaining fat.” But It could not be fat at all, it could just be water weight. And that’s usually the first thing that happens in a quick kind of situation, over the course of a week or two, where you’re like, “Oh man I don’t know what’s happening, but I look terrible.” And, “Oh I have stress, and I’ve got a lot of training load,” and all that. And so it’s also a great example of how delicate sort of the stress recovery balance is, right, I mean you’re training awesome, you’re eating a lot of calories. Life is good in that zone if you love training, you’re probably getting stronger but you’re only like one hair’s width away from the wheels falling off the system, and that could be the psychological stress at work, or just simply not even something causing anxiety, but it could just be extra load. So you’re like, “Things are great, but I’m just doing more.” And then you get that sort of predictable feeling where you’re like, “Oh, I’m not feeling as great as I was, I am looking weird. Emotionally things are different.”

And so that’s why it’s one of the reasons as I’ve gotten older, I’ve undulated my training. So for the people who are very into training this is sort of and advanced strategy. When things are going as great as you’ve described when you got back from vacation, I know right around the corner, what you described later is going to happen. So I actually undulate my training, so I modulate my volume over four week periods so that during any four weeks, I only have one very, very high intensity week. One just below that, one in the middle, and one very low.

So even if I don’t think I need it, my training’s undulating so that I’m not always that one hair’s width away from breakdown, you know what I mean?

Brett McKay: I know what you mean. Man, but I really miss those days when I could eat 4,100 calories. I was able to eat two Little Debbie brownies and not feel bad about it. It was wonderful, but easy come, easy go. We’ll get back there again sometime.

You also mentioned sleep plays a role in our metabolism, and I imagine that just goes to stress management and recovery, et cetera.

John Berardi: Yeah, I mean simple sleep deficit causes some interesting challenges. I have a friend who’s a sleep expert at UCLA, and I love unpacking some of this with her because it’s so fascinating to see what the research is saying in this area, but altered processing of glucose in the body, increased stress and sympathetic nervous system activation. Risk of obesity and diet, it’s the same things as stress, and I think they paly a role in each other.

Oftentimes when we have an up-regulation of stress, we have a really difficult time sleeping, and then that difficult time sleeping creates more stress, so it becomes that kind of cycle, and then vice versa. Sometimes when we’re not getting enough sleep, we get really stressed about it, and then that stress causes the problems of stress, and then that causes more sleep deficit. But it’s all wrapped up. When you don’t have strategies, the one thing I hate is the conclusion is then, be less stressed, or sleep more.

Well, those aren’t strategies, that’s just finger wagging. So I’d love to talk about some of the things about that, but yeah. Ultimately, neither of them has dramatic effects on our total daily energy expenditure, but what they do is shift how we metabolize nutrients, the hormonal status of our body, the immune system status of our body. We all know stress and sleep deprivation leads to often a lot of people getting sick more frequently.

So all these things are happening, and I mean you can’t have good workouts, and you can’t make good choices at the dinner table when you’re stressed, and you have a sleep deficit. So I think when it comes to weight gain, this is the primary driver. It’s behavioral. Stress and sleep deficits lead to behavioral changes, that then cause you to be out of energy balance. But then there’s obviously the hormonal stuff happening, too. Which I don’t think is as powerful a driver of some kind of medical, internal system being broken and causing magical fat gaining. It’s usually hormones then drive certain behaviors that make you eat more, or burn less.

Brett McKay: So listening to this conversation made me think of this idea that people have like, “Oh I’m getting older, my metabolism is slowing down, that’s part of life.” But it sounds like it’s not so much the fact of getting older caused your metabolism to slow down, it’s just that as you get older, you probably move less, you’re probably eating more. You’re probably more stressed because you’ve got all those other commitments going on, and as long you take care of some of that stuff, your metabolism can be just as fine as it was when you were 30, or 20.

John Berardi: Yeah, I mean it’s just so hard to remember, isn’t it? People will say, “Well, now that I’m in my 40s, my metabolism slowed down. I’m not less active, I actually go to the gym now and I didn’t in my 20s, and so it has to be something about my metabolism.” But it’s just so hard to remember. I don’t know if you ever watched that show Explained on Netflix that Vox puts out, but it’s excellent, they do these 20 minute episodes on various topics, and they just did one called Explaining the Mind and it was on memory.

And it’s just so fascinating how bad we are at remembering. Even Daniel Gilbert’s work on happiness, he basically talks about how people are terrible at remembering how we felt about things in the past, even the activities themselves, and we’re even worse at predicting how we’ll feel about things in the future. So the idea that I’m going to come up with a story that somehow I remember what I was up to 25 years ago when I was in my early 20s, and I can compare that accurately to how I am now in my late 40s, it’s folly.

So as you described, I mean the metabolism generally isn’t slowing down as we age unless we lose body mass, lean mass, or we do less physical activity, which for a lot of people, and again, it’s not just going to the gym. It’s all the activities of daily living. So if we account for those, if we maintain or build lean mass, if we find ways to do more activity, if we take care of our sleep and stress management, then body weight and metabolic things should not be a problem as we get older, at least as we talk about the management of body composition and body weight.

Brett McKay: So let’s talk about what are things that people can do after listening to this episode to… I don’t know, they can’t control completely their metabolism, but take more control over their metabolism.

John Berardi: Yeah, I mean if we’re talking about metabolism, the only thing that we can drive is the activity piece, right? But when we talk about sort of getting in shape, then again it’s sort of these four things we need to look at, exercise, right? So, mixed modal exercise. Do something daily, doesn’t always have to be a workout, right. And it’s something with an interval sort of component to it. It’s hard for a bit, you rest for a bit, hard for a bit, rest for a bit.

Sometimes when I travel I just go to a hotel gym, I get on the treadmill, I put it at a fast pace, I run for 30 seconds, then I jump off it for 30 seconds. And I do that like 10 times. It lasts five minutes. It’s really hard, but it’s only five minutes.

And then so there’s your intervals. And then you do some kind of strength training. And then you do some kind of parasympathetic recovery. Go for a hike in nature. Go for a walk around the neighborhood. Go for a bike ride, that kind of stuff.

So that’s the first component. People have to get this in their lives. If you want weight management, and body composition as part of your goal set, you have to do mixed modal exercise like this.

The second thing is let’s talk about sleep. Right, progressively moving towards eight hours a night. All the research suggests that less than that is too little. And it doesn’t matter how individually special you think you are, if you’re doing some kind of weird sleep protocol where you think you can get away with five hours a night, the research shows again and again and again, physiologically that close to eight hours a night is ideal. If you’re a parent with you kids, I get it. You’re not going to be getting that. We have four children at home, I understand.

But I’m not saying go to eight hours tonight, I’m saying progressively move towards. Every few extra minutes that you can get, versus what you’re getting now helps. And how do you create that? With better bed time routines. Are you winding down, are you getting off electronics, are you avoiding caffeine, are you avoiding the foods that can keep you up at night. Are you doing a brain dump before you go to bed to get out all the thoughts that, “Oh I got to remember this tomorrow, and that tomorrow.” Well if you write it down, you don’t have to remember it, you don’t have to think about it while you’re laying in bed.

Are you doing breathing, are you doing mindfulness, are you doing meditation type stuff as you lead up to this to clear your mind? Are you setting the temperature correctly in your room? For a lot of people, simply lowering the temperature of their bed, or their bedroom to mid-60’s, low 60s can make a big difference in their ability to fall, and stay asleep. This last year, I bought this device called a chiliPAD, that you just lay under the fitted sheet in your bed, and you can control the exact temperature of your bed. And there’s two zones, where if your partner needs to sleep at a different temperature than you, you can. And so I sleep at like 55 degrees, so I can actually tuck under the covers, and I can go totally dark. Like, cover up my head with my blanket and my sheet. Go totally dark, but my side of the bed is kept at 55 degrees, it’s amazing.

There’s things like CBD, and other things people are doing for sleep. So these are all just options I throw out there, as you progressively move towards trying to get more hours of sleep in a night. Stress, stress management. One of the top things people can do, counterbalance all your sympathetic activity with parasympathetic.

Sympathetic is high intensity exercise, it’s stress at work, it’s all that kind of stuff. So what will you do to counterbalance it? Going for a walk in nature, going for a walk outside. Listening to music. Having a bath at night. Ways to wind down and get this sort of sympathetic, it’s usually called your fight or flight system, and parasympathetic is called your rest and digest system. So trying to activate that rest and digest system.

A long time ago, even before the current sort of resurgence of cannabis research and things like that, a group of athletes I was working with, strength and power athletes, were using cannabis regularly. And most of the coaches would sort of judge that behavior as sort of morally wrong, and I was just really curious why they were doing it, because they were doing it so regularly. And they kept talking about how it enhanced their training, and so when we unpack that, oh I realized oh it’s not that is a magical ingredient in your training protocol. This was just the only parasympathetic activity you were doing, your only rest and digest activity.

So I was like, “Okay cool, maybe we don’t need to smoke weed every night, guys. Maybe we can do these other strategies to counterbalance our sympathetic nervous system.” And so that’s our stress management part. And then on the nutrition side, I mean the interventions for most people are fairly straightforward. Most people starting to pay attention to this for the first time have a bunch of what we’ll call subclinical deficiencies. So they won’t be getting enough protein, they won’t be getting enough omega-3 fats. They won’t be getting enough water, and they won’t be getting enough vitamins and minerals from their food intake.

So then when we correct those, and then we find strategies to not eat too much, usually people are able to manage their body composition well. Now, there’s so many ideas, we could do a whole nother podcast on low carb versus moderate carb, keto and paleo, and plant based eating and all that stuff, but I think most of them work because when you pay attention to what you’re eating, and you set up a bunch of rules, those rules prevent you from eating too much.

And if you have a book to sell, that’s a really short book. So you have to then talk about why plant-based does X, Y, and Z, physiologically, or why all meat does X, Y, and Z, physiologically, but I think the biggest driver, because we know people who eat let’s say keto, and we know people who eat plant-based, and in both cases there are people who look great, feel great, perform great on either one of those, so we have to look at what’s common between them.

And what’s common is that both of them help prevent eating too much. And so whatever strategy you use, I mean we often teach people to just get really in tune with the hunger and appetite awareness. So we do that by having them practice for a week or two eating slowly. It’s not a life practice, necessarily, although for some people it needs to be. But it’s a practice, to start to get in tune with our appetite cues, and then eat until satisfied, not stuffed.

So that’s the next practice we do for another week or two. And we train people on what stuffed feels like, what satisfied feels like, what still a little hungry feels like, and we help them get into that zone where they’re paying attention. And then once their protein, omega-3s, water, and vitamin intake is good from eating lots of fruits and vegetables, then when they can just regulate through eating until satisfied, not stuffed, and again it takes a while to practice this and learn the skill, then we don’t need to count a lot of things, or restrict a lot of things.

So whether this is a metabolic health protocol or not, it has a lot to do with weight management, body composition. So again, exercise mixed modal, sleep, any extra minutes are positive. Stress, you got to find something parasympathetic to do in your life. And then nutrition. Get rid of those four basic deficiencies, and find ways not to eat too much. I mean this is the prescription for anyone who wants to look, feel, and perform better.

Brett McKay: Well, John, where can people go to learn more about your work?

John Berardi: So if you’re listening, and you want to check out strategies, articles, for looking, feeling, and performing better as I just mentioned, we have over a thousand of them for free at So if you’re kind of looking for having all your nutrition questions answered, we’ve probably answered every question you could possibly have. What do you think about dairy, what do you think about keto. What about plant based diets, how do I lower my blood pressure, how do I lose 20 pounds? We’ve written about that.

Definitive research based, evidence based articles, so you can come to, and then my newest project is actually for people who work in health and fitness, or who want to. It’s called the Change Maker academy, so it’s and so I wrote a new book for people working in health and fitness, or who want to, to help them turn their passion for health and fitness into a meaningful purpose and a successful career, and it’s called Change Maker. And so if people pop over to they can download a free sample of the book, and those are the two places people can come check me out.

Brett McKay: All right, well John Berardi thanks so much for your time, it’s been a pleasure.

John Berardi: Thanks man, I appreciate you having me, and I hope everyone who spent the time with us learned a little bit today. Not only just learning but they have some next actions that can make a difference in their lives.

Brett McKay: My guest today was John Berardi, he’s the owner of Precision Nutrition. Check out where you can find out more about the services there, as well as lots of free content about diet and nutrition. Also check out his website where you can learn more about his new book, Change Maker, it’s available on And check out our show notes at, where you can find links to resources where we delve deeper into this topic.

Well that wraps up another edition of the AOM podcast, check out our website at, where you can find our podcast archives, as well as thousands of articles written over the years about nutrition, exercise. Got articles about how to dress better, how to be a better husband, better father. You name it, we’ve got it.

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