Is exercise or nutrition more important for weight loss?

In the context of human history, our transformation into couch potatoes happened in the blink of an eye. Only 100 years ago, most people relied on manual work to make their living.

Today, things are different. Many of us live our lives in front of a screen. Online shopping and remote work mean some of us don’t need to leave the house at all. So, how bad is this for us? 

The answer is now clear: Low levels of physical activity lead to an increased risk of disease and a lower quality of life in older age. However, when we come to the question of what sort of exercise you should be doing, how often, and how much it contributes to weight loss, the answers might surprise you.

In this podcast, Jonathan speaks to a human physiologist to learn about the interactions between diet and exercise and their impact on human health.

Dr. Javier Gonzalez is an associate professor of Human Physiology at the University of Bath and also a technical advisor to the athletes in the INEOS Tour de France cycling team.

If you want to uncover the right foods for your body, head to and get 10% off your personalized nutrition program.


[00:00:00] Jonathan Wolf: Welcome to ZOE science and nutrition, where world-leading scientists explain how their research can improve your health.

We've all heard the message. Exercise is important. We should all go to the gym more often. If we want to lose weight, we need to exercise. But how much of this is true in the context of human history, our transformation into couch potatoes happened in the blink of an eye. Our hunter-gatherer ancestors needed to venture out daily to find new sources of food.

Only 100 years ago. Most people relied on manual work to make their living today. Things are different. Many of us live our lives in front of a screen, online shopping and remote work mean some of us don't need to leave the house at all. So how bad is this for us? The answer is now clear. Low levels of physical activity lead to an increased risk of disease and a lower quality of life in older age.

However, when we come to the question of what sort of exercise you should be doing, how often, and how much it contributes to weight loss, the answers might surprise you. The fitness industry, like the diet industry, seems to present a brand new trend every month. So in today's episode, we'll find out what the latest science says.

Answering questions like, how important is an exercise for weight loss can fasting make exercise better for our health and how much exercise do we really need to do to see the benefits. To answer these questions and more I'm joined by Dr. Javier Gonzalez associate professor of human physiology at the University of Bath, whose research has focused on understanding the interactions between diet and exercise and how this impacts human health and disease. Javier is also a technical advisor to the athletes in the INEOS tour de France cycling team. Javier, thank you for joining me today. So why don't we start with a quickfire round of questions from our listeners?

Maybe just a yes, no. Or, you know, a one-sentence answer, if you can, and then I'm sure we'll go into some of this in some more detail. So let's start with, is exercise the most important thing for weight loss?

[00:02:21] Dr. Javier Gonzalez: For most people? No. 

[00:02:24] Jonathan Wolf: Okay. Interesting. Does a walk count as exercise? 

[00:02:30] Dr. Javier Gonzalez: It depends on how you define exercise, but again, for most people, yes.

[00:02:35] Jonathan Wolf: If you're working out, do you need to eat lots of protein powder? 

[00:02:39] Dr. Javier Gonzalez: No. 

[00:02:40] Jonathan Wolf: Does too much cardio stop you from burning fat? 

[00:02:45] Dr. Javier Gonzalez: No. 

[00:02:47] Jonathan Wolf: Is exercise important during menopause? 

[00:02:51] Dr. Javier Gonzalez: Yes and exercise, I would argue is always important. 

[00:02:55] Jonathan Wolf: Fantastic. I love this question that we got on Instagram is yoga effective for weight loss?

[00:03:02] Dr. Javier Gonzalez: Probably not as effective as other forms of exercise, but it does have the benefits. 

[00:03:07] Jonathan Wolf: Okay, brilliant. We should come back to that. And a related question. Do you need to be doing both weightlifting and cardio to get benefits from exercise? 

[00:03:16] Dr. Javier Gonzalez: To get all of the potential benefits that exercise can offer, then the answer is probably yes.

[00:03:23] Jonathan Wolf: Okay. And last question. Do men and women respond to exercise in the same way? 

[00:03:29] Dr. Javier Gonzalez: No, but there's plenty more as well, that influences that response that I'm sure we can get into. 

[00:03:34] Jonathan Wolf: Brilliant. All right. Well, I think that will be quite a few ounces there that will surprise many of our listeners and one or two that surprised me, but why don't we start at the beginning, and then we'll sort of dig into all of this in more detail. Javier. why does exercise matter for health at all? 

[00:03:50] Dr. Javier Gonzalez: So exercise is crucial for health probably because we evolved in an environment where we need it to have a high level of physical activity. And nowadays, of course, most of us, or a lot of us have jobs that are desk-based and our lives are relatively sedentary. We end up doing less leisure time activity quite often as well.

And so we're not well adapted to that environment that we're living in nowadays. And exercise has a number of benefits. It seems to affect almost every single tissue in the. We commonly think of it as improving perhaps our heart health, also our musculoskeletal health, the health of our muscles, and our bones, but it seems like it even affects things like our fat tissue and our brains, and almost every single tissue in the body is affected by exercise.

[00:04:42] Jonathan Wolf: And so how much exercise do you need to do to start to get those health benefits you're talking about? 

[00:04:50] Dr. Javier Gonzalez: Yeah, the government guidance would be something like, it depends on which country, but at least in the UK, the government guidance is to do at least 150 minutes a week of moderate-intensity exercise or 75 minutes per week of vigorous-intensity exercise.

Plus two strength sessions. Now that's an okay starting point for the general population, but everything counts. So as little as 10-minute bouts of any form of physical activity can start to accrue benefits. And the general advice is the more, the better. So. A very rough guide and I'm sure different people will respond differently to exercise and some may enjoy certain forms of exercise.

So in that scenario, I think the simplest advice would be to do what you like and do as much of it as you enjoy it. 

[00:05:41] Jonathan Wolf: And is there a minimum amount at which this sort of starts? So, you know, if I just walk around the block really slowly, where does that start? Because those words you describe moderate exercise. Like what does it mean? Javier. 

[00:05:54] Dr. Javier Gonzalez: Yeah, it's a great question. Because actually, we should probably define what exercise is in terms of how that relates to physical activity. So physical activity encompasses every bodily movement that we make that increases the amount of energy we're burning and it doesn't actually have to include movement.

So that's the textbook definition. I actually prefer the definition of muscle force production. And the reason I prefer that is because if you're sitting at your desk right now, the muscles around your torso are stabilizing. That torso your spine and everything, and that's got an energy cost to it.

So you're expending more energy sitting upright than you would be lying down on the bed. And so that's already a form of physical activity or at least an increase in energy expenditure. So any muscle force production, anytime your muscles are contracting, you're burning a bit more energy and that contributes to overall physical activity.

[00:06:51] Jonathan Wolf: So I'm working out right now while sitting on my ass. Is that what you're telling me, Javier? 

[00:06:55] Dr. Javier Gonzalez: Exactly. At the very latest level, but yeah, you can feel good about yourself. 

[00:07:01] Jonathan Wolf: I'm guessing that's not enough though. To meet the criteria you were describing. 

[00:07:06] Dr. Javier Gonzalez: No, no, and, where exercise comes in. It's a bit of a funny definition because it really depends on your motivation.

So if you go for a walk and that walk is part of a task like you are walking to the shops, that might not count as exercise, but if the intended purpose of your walk is to improve your health or fitness, then it comes under the definition of exercise. So. I actually prefer the term physical activity to exercise because physiologically that's, what we're really interested in is all of the energy expenditure.

And when we're talking about moderate-intensity, physical activity activities like brisk walking and starting to get your heart rates slightly elevated, but still able to hold a conversation. When we get into vigorous intensity, that's where you start and not be able to put a full sentence together without taking a breath.

[00:07:57] Jonathan Wolf: Got it. So that's like when I walk with my friends who are much taller than me, and I'm just trying to keep up that's, that's it. I like the idea of a brisk walk because it comes up actually in quite a few of these, and actually, that is the first level that might really make a difference to your health. Right? Which is a lower bar than many people expect, which is what if I'm not going into the gym pumping iron, like none of this counts. For how long would you need to do that? To start to get some of the health benefits that you were talking about with physical exercise? 

[00:08:23] Dr. Javier Gonzalez: Yeah. You can start to see some quite profound benefits actually, with as little as 30 minutes of brisk walking per day, and that doesn't have to be all in one go. So you can split that up into five or 10-minute bouts across the day and accumulated over the day can actually start to improve things like your blood lipid levels. That was the fat in the blood.

[00:08:43] Jonathan Wolf: So that's pretty amazing. So you're saying that 30 minutes a day of the brisk walk actually can make a profound difference to like measurable markers in our blood and that we don't even have to do it all at once. You're actually saying, you know, I could cheat and do that in three or four different pieces.

[00:08:58] Dr. Javier Gonzalez: Exactly, exactly. 

[00:08:59] Jonathan Wolf: That sounds quite counter to what I think many of us would imagine. Let me come on to the related question that a lot of people are asking us to discuss before this, which is this idea of cardio versus sort of strength, training, or weightlifting. And firstly, could you just explain what those things are because they're words that we hear and I think many of us aren't really clear exactly what they mean and then explain, like why is there this difference? And does it matter for people thinking about this for their health and probably their weight as well? 

[00:09:28] Dr. Javier Gonzalez: Yeah. Sure. So when we're talking about cardio, I guess most of the time we're talking about, well, at least in the scientific area, we would probably call it endurance exercise. I guess the term cardio comes from the idea that most of the adaptations you get are in the cardiovascular system.

And these are things right from the lowest intensity of brisk walking through to running, cycling, swimming, and that kind of thing, where you might do an exercise session that lasts for 30 minutes up to an hour, you get some athletes doing very long training sessions of four or five hours of this type of exercise.

Then strength training might be doing weights in the gym where you are lifting weights, maybe from five to 10 repetitions, and repeating that in sets, it doesn't have to necessarily be lifting weights. Strength training does also includes bodyweight exercises. So it could be things like squats. So bodyweight, squats, things like press-ups and pull-ups, but even actually for - people who are slightly advanced in age, even just getting up and down from a chair, a number of times can be a form of strength training that can help improve that their capacity for daily living. Really. 

[00:10:41] Jonathan Wolf: And what's the difference, cause you talked about the time, but what's going on physiologically that differentiates these? And then can you explain a bit what impact that has and why it matters? 

[00:10:50] Dr. Javier Gonzalez: Sure. So they do sit on a spectrum. So you can get areas that slightly overlap. And you can probably envisage that if you think of something like cycling up a hill, a very steep hill, there's a point where that probably turns into more of a strength workout on your legs than it does a cardio workout. So the force of you pressing down on the pedals crosses over into that strength workout and flip it the other way round, where you might be doing a circuit class in a gym session, you might be using weights, but it's relatively lightweight and you're lifting a lot of reps and that can transition into a cardio workout.

However, if we go to the extremes of cardio versus strength, then they do have quite different adaptations. And that's why the advice would be to get all of the health benefits of exercise. It's good to do both cardio and strength work and the cardio exercise will improve things like your cardiovascular system.

So your heart can get stronger. Your blood vessels become more compliant or more elastic if you like, so they can help lower your blood pressure. Whereas with strength, training, you get a number of other adaptations. So your muscles clearly can get stronger, but even your ligaments and tendons can get stronger.

And I guess one of the things that people often don't think about is bone health, heavy strength training can improve your bone, mineral density and so improve the strength of your bones, also. 

[00:12:18] Jonathan Wolf: I think maybe just to talk about that second bit, this is one of the reasons why strength training is not just for people who are in their twenties and look amazing on Instagram.

Right? There are real health linkages could just talk for a minute more about that, because I think often we think about strength training perhaps has been very much about sort of the body beautiful, but there's more to it, right? 

[00:12:38] Dr. Javier Gonzalez: Oh, absolutely. So our strength will typically peak when we're about 30 to 35, maybe 40 for some of us if we're lucky and then it will gradually decline after that point.

Almost no matter what we do. However, by doing strength training, we can slow that decline. And the aim is that there'll be a certain point where we gradually just become weaker as we get older. And there'll be a point where even getting out of a chair or lifting the shopping bags, is now becoming too difficult.

We're not strong enough to do that. And so the idea is if we can maintain strength training, we can delay the point at which getting out of the chair is now impossible to do alone. So it becomes really important for healthy aging, not only from that strength standpoint but also then the bone health. So if we do have a fall we're less likely to fracture the bone because the bone has a greater bone mineral density. 

[00:13:31] Jonathan Wolf: Got it. And what's going on between these two? So there's obviously stuff going on at a very physiological level, which is quite different between this cardio exercise, which you're talking about going on for a long time, and just sort of strength training, where I'm just doing this in a very short period of time.

Can you help us with that a little bit more about what's going on, how that ties, I guess, to like our energy system, because I think that it's going to start to bring us through to nutrition, which obviously we're very interested here as ZOE? 

[00:13:55] Dr. Javier Gonzalez: Yeah, sure. So it's probably worth starting with strength training.

So things that are very short duration, they're almost like mini bouts of exercise and the energy we use there and then extend to the longer duration exercise. So with strength training, when you initially do a very high-intensity movement, let's say you lift a weight with your bicep. The main energy system you're probably using, there is something called the phosphocreatine system.

And that's commonly why people who left a lot of weight sometimes supplement with creatine, because that can increase the creatine stores in the muscle, and that can help that energy system so they can do more repetitions without fatiguing. But, that doesn't really use the fuels in the same way that longer duration exercise does.

So when you increase to longer duration exercise, one of the benefits of cardio is that you're burning through energy, and the main fuels that we use there are carbohydrates and fats. So one of the other differences between cardio and strength training is that with cardio, we're going to be burning through total energy more than strength training on the whole, and we're going to be burning through our carbohydrate and fat stores. In addition to that, we get high heart rates. That's maintained over a long period of time. There's a way to blood flow through all of the circulatory systems. And that's why we get those adaptations in blood vessels as well.

[00:15:20] Jonathan Wolf: Because our body sort of has to improve the way in which you can get this energy to these muscles that are working away.

[00:15:26] Dr. Javier Gonzalez: Exactly. That. 

[00:15:28] Jonathan Wolf: You know, I think one of the biggest questions that we all ask, is, is exercise or nutrition more important? 

[00:15:35] Dr. Javier Gonzalez: So if you were to ask me weight maintenance, I would answer very differently. For weight loss, for most people, diet is almost certainly more important than exercise. And I guess just to validate that, for most people, it's a lot easier to eat energy than it is to burn energy. So as an example, a typical one-hour gym session for an average person might be about 400, maybe 500 kilocalories of energy. Now, my bowl of porridge in the morning, or oatmeal is easily over 500 kilocalories of energy. And so in a small bowl, you can easily overreach what you've may have just burned in the gym. Now we should also remember that our resting metabolic rate is constantly going on. So we're constantly burning a baseline level of energy. So we shouldn't try to always offset what we burn through exercise, but clearly, exercise. Doesn't make a big dent in our energy budget compared to how easy it is to eat those calories. Now, it is a very different way than the athletes that we can maybe come onto later. But for the vast majority of people, that's the general. 

[00:16:49] Jonathan Wolf: Which I think is really interesting. Right. And it's quite counter to, I think a lot of the messaging that we've heard over the last 30 or 40 years, some of which I think comes from very large food companies that have a particular angle to deliver there where, you know, I think the story we're told is, you know what, everything to do with weight is because people aren't doing enough exercise.

And, you know, if only people were doing more exercise, it'd be fine. And therefore, you know, it's fine to sell sugary drinks in schools is my favorite example of this. The kids, you know, as long as there's a playground because after all they could just go and burn this off. And I think what you're saying is obviously exercise is really important, but you can't just go and do a bit of exercise to burn off eating all of this incredibly poor quality food that, you know, we're all surrounded by now in the developed world. 

[00:17:37] Dr. Javier Gonzalez: Exactly. I guess the way I would frame it is probably the exercise has a number of benefits, but we shouldn't expect that just by beginning exercise, we will lose weight. It can actually help control appetite and it can help with things like body composition, but that's when in conjunction with diet. So really, yeah. Diet comes first, but exercise can really help us achieve. The goal that diet is, is achieving. 

[00:18:04] Jonathan Wolf: Now you're doing some really fascinating research actually about the interaction between fasting and exercise. Right? Which also, I think really challenges this idea that, you know, a calorie is just a calorie and that a good diet is about, you know, making sure that the number of calories in equals the calories out. Can you tell us a bit about this research that you've been doing and what it tells us? 

[00:18:27] Dr. Javier Gonzalez: Yeah, sure. So we've done a series of studies now and we're continuing this line of work. And with the short-term studies where we studied people for about 24 hours, we might ask them to skip breakfast or eat breakfast and exercise or rest.

And we tend to find that when they skip breakfast and exercise, they burn more fat, during that bout of exercise and that's been known for quite a long time. We tend to burn about 20% more fat when we're fasted in that overnight fasting state compared to say an oatmeal-based breakfast. I'll try to understand then if that continues over a full training program because what we see in a 24 hour period might be very different over a six or 12-week timeframe.

So. One of my former Ph.D. students ran a pretty intense study where he fully supervised every single exercise session. He recruited 30 men to complete this six-week training program. And he measured the amount of fat and carbohydrate they were burning every 15 minutes. So every single training session over a full six weeks.

And we did see with the very first session, the group who were performing that exercise in a fasted state were burning, almost double the amount of fat actually in this study, compared to those who were performing the exercise in a fed state. Those lines were parallel throughout the six weeks of training.

So as people became fitter, they were all bought burning more fats. But the group who were in the fastest state was still burning more fat at the end of the training program than the group in the fed state. Now, this links into the idea that it's more than just calories because we did actually give both groups the same number of total calories.

Before and after the session. So the only difference was the timing in which they consume those calories. So whilst one group was burning more fats, both groups had the same energy balance. And so they had the same weight loss throughout the whole study. So for weight loss, it seems to be more about energy balance, than it does to be about fat burning or fat use, but for other health outcomes, that's where it became really interesting. So we found that the people who are burning more fats actually improved things like their glucose control and their insulin sensitivity to a greater extent than the group who had breakfast before exercise. And weren't burning through that fat stores. 

[00:20:56] Jonathan Wolf: So, what you're saying is actually that we're getting the same number of calories, but some of these people were exercising, fasting, and somehow this is changing the way their body was working. And you were seeing these measurable and sort of clinically important improvements in these health markers that you would expect to, you know, have an impact on their long-term health because their body was getting better at burning fat than burning blood sugar. Is that the right way to understand that? 

[00:21:20] Dr. Javier Gonzalez: Yeah. Yeah. We think it's something to do with the turnover of fat stores within probably within the muscle. So if you think of our fat stores, we store most of our fat in fat tissue, but we also have these small fat droplets within our muscle, an important fuel stored within the muscle. But what we find is in people who are sedentary, these pools of fat in their muscle, you can almost think of them as stagnant pools and you get a buildup of toxic metabolites and they seem to interfere with the muscle's ability to respond to insulin and to take up glucose out of the circulation, take up sugar out and bloodstream.

And what we think is going on here is that. By performing exercise in a fast state, you burn those pools in the muscle. They're turning over more quickly. They're not stagnant. You don't get that buildup of toxic metabolites. And so the muscle is healthier. It can take up more sugar out of the bloodstream more effectively. 

[00:22:16] Jonathan Wolf: And so does that mean we should all be doing all of our exercise in a fasted state? Does it just mean that you know, when I take my daughter to school and push her for 30 minutes, it feels like a brisk walk? She's getting heavier than a, at least I should do that before I have breakfast. How do I, how do I think about applying this and how should our listeners think about applying that to their lives?

[00:22:36] Dr. Javier Gonzalez: Yeah, it definitely depends on what your particular goal is and might even depend, on you as an individual. So I should caveat that we have only currently run this study in men, in middle-aged men. And we are keen to do this study in a wider population, including women as well. But the other thing to consider is what your goal is. So if, for example, you want to do an important session. You want to work hard in your session or as hard as possible, then actually having breakfast is a good thing because your performance will be impaired if you haven't had breakfast and that's even if your exercise session is in the evening.

So there have been studies. People either eight or skip breakfast in the morning, they all have lunch at lunchtime, but that performance in the evening was still impaired when they had skipped breakfast in the morning. So my advice for somewhat, for the kind of average person would actually be to mix it up.

So perhaps do two or three sessions a week where you might perform them in a fasted state and other sessions in a fed state. And. Everything in biology and physiology is about trade-offs that are actually potential downsides to performing exercise in the fastest state as well. 

[00:23:48] Jonathan Wolf: And if I'm listening to this, and I'm not only thinking about health improvements, which is obviously incredibly important, but I'm also thinking about weight loss. How do I understand that? Cause you said: "Hey I'm now burning fats people like, well, that's good. I want to burn some fat", but then you also said actually, because what you actually saw was not a change in weight loss between these groups, because you fed them exactly the same amount of food, which is a bit artificial, I guess, compared to what they might do naturally.

How do people think about this for weight loss? Do you have the data yet or is that also part of the future studies? 

[00:24:19] Dr. Javier Gonzalez: Yeah, that's part of our future studies. From our short-term studies, it seems like if you don't force people to eat what they had skipped before exercise, then actually, over 24 hours, they don't fully compensate for having done their exercise in a fasted state.

And so if that continues over the long term, then they may lose more weight. But yeah, I'd be very hesitant to say that because we know that long-term exercise or appetite are very different from the short-term. So we hope to have the answer in a year or two's time. 

[00:24:51] Jonathan Wolf: Well, we'll be excited to talk about it. And as you know, this is an area we're really interested in helping to support as well. So I think the playback here I think, is doing some exercise in a fasted state can be really beneficial for health. And I'm hearing you say potentially also from what you've seen support for weight loss, but that, that is not really proven by the data yet, because as we know, you can do these 24 hours studies, and then you translate that into three months and suddenly, you know, these effects get balanced out, which is part of why this science around everything to do with nutrition and exercise is so complicated. Right? 

[00:25:26] Dr. Javier Gonzalez: Yeah, absolutely. And I think it's probably worth just mentioning as well. If people are going to try this exercise in a fasted state, especially people who are perhaps concerned over bone health, it might be worth taking some calcium before those sessions, because one of the downsides of that type of exercise is its probably a catabolic state for the bone. 

[00:25:46] Jonathan Wolf: Javier, what does that mean?

[00:25:48] Dr. Javier Gonzalez: So the bone is in a state of breakdown. 

[00:25:51] Jonathan Wolf: Okay. It doesn't sound good. 

[00:25:53] Dr. Javier Gonzalez: Uh, no. And it's probably because when we exercise, we sweat out salts as we might be aware of, but we also actually sweat out calcium as well, but it has been shown that taking some calcium before a bout of exercise in a fasted state can help prevent some of that bone breakdown.

So for certain populations, I would advise taking some calcium before those sessions to try and prevent that. 

[00:26:19] Jonathan Wolf: And if I'm doing a brisk walk, am I worried about that, even? Or is that more like a more energetic activity where then you're describing than that? 

[00:26:28] Dr. Javier Gonzalez: Yeah, you're probably okay with a brisk walk, but this is probably more relevant for athletes doing this type of training more vigorously.

[00:26:35] Jonathan Wolf: Bringing up professional athletes, I think is a great way to talk about your work with, I think some of the most amazing athletes in the world, right. Professional cyclists. And I know that you work with the INEOS tour de France team. They seem like almost a different species of person than I am. Is there anything that you do there that you think is relevant for ordinary people listening to this call? And indeed also what is really different? So how do we learn from this? For those of us who are not these super athletes? 

[00:27:05] Dr. Javier Gonzalez: Yeah. I think you're absolutely right. They are a completely different species in many ways.

There are some things we can certainly learn from them. And actually, the idea of performing exercise in a fasted state really stemmed from professional sports, running and cycling in particular where these athletes would do exercise sessions, not just in a fasted state, but they would train twice a day.

So their first session would really deplete their carbohydrate stores. They would then eat low carbohydrates at lunch and maybe do another session in the afternoon. And so they're really pushing the limit on almost taking that fasted exercise to the next level. And the idea behind that is that one of the stimuli to adapt to exercise is a low glycogen concentration in muscle.

And what that is is it's our storage form of carbohydrate. So when we store carbohydrates in our muscle, it's in the form of glycogen. 

[00:28:03] Jonathan Wolf: So Javier, because we talk a lot about blood sugar, right? So when we eat carbohydrates like rice or bread or Coca-Cola or whatever, it turns into this blood sugar, just help us understand then.

So how does glycogen fit with that?

[00:28:15] Dr. Javier Gonzalez: Sure. So the blood sugar or glucose in the blood will be taken up by muscle during exercise which happens independent of the hormone insulin, but when we're at rest, we have a meal, we get an insulin response and that insulin will help drive that sugar into the muscle.

Once it's into the muscle, it has two fates, if you like. One will either be, it will be burned as fuel. And the other will be that it will be converted into glycogen. So that's where it's stored in. It's a kind of fuel tank if you like within the muscle. 

[00:28:46] Jonathan Wolf: Got it. And you said there's a limited amount of this that's in the muscle. Could you explain that for a minute, then that ties in, I guess, to what you're describing with these, super athletes? 

[00:28:56] Dr. Javier Gonzalez: Sure. So, whereas our fat stores are for all intents and purposes limitless, we could just run for days and days and days on our fat stores. Our glycogen stores will run out very quickly and it's actually why people often have it hitting the wall during the marathon where after about 90 minutes or so of vigorous-intensity exercise, those glycogen stores will be pretty much completely depleted. And we have to really drop the intensity. 

[00:29:23] Jonathan Wolf: I think, I think I hit the wall quite a bit sooner. Happier, but yeah, so. 

[00:29:28] Dr. Javier Gonzalez: So it, yeah, it will run out very quickly. And when that glycogen is low, that seems to be a signal that starts a cascade of events in the muscle that stimulates some adaptations. So the kind of the idea behind training in this depleted state was that you're ramping up the volume on that signal to adapt. So it really stemmed from professional athletes and it's now starting to filter into the health area. 

[00:29:53] Jonathan Wolf: Got it. So these people, you know, they're saying I'm using up all of that glycogen, I'm continuing to exercise hard. So I've got to find other ways to create energy and they can't just be the blood sugar you're saying, 'cause they're intentionally not eating meals with, you know, they're not drinking sort of sugary drinks to keep this going. So they're presumably having to get to burn fat. Is that what they ended up having to do? 

[00:30:13] Dr. Javier Gonzalez: Yes, exactly. Yeah. And so they're burning fat in that state and the downsides of burning fat as a fuel is. It's a relatively slow-burning fuel. So you can think of it as a kind of diesel fuel, whereas our carbohydrates are petrol.

And so you do have to lower the exercise intensity when you're burning fat as fuel. So it's more the kind of low intensity and duration sessions that they might do this type of work with. 

[00:30:38] Jonathan Wolf: And you're creating sort of flexibility then, are you? Like, I've got this ability to run on both these fuels and it's, that's a good thing, is it? 

[00:30:46] Dr. Javier Gonzalez: That's the ultimate goal. Yeah, because especially. Athletes, do need to be able to burn fat as fuel when appropriate. So at those low intensities, they still need to be able to burn carbohydrates as fuel. When the race really gets going, they need to sprint up a hill or sprint to the finish line.

That's a carbohydrate-dependent activity and it's where different modes of training and nutrition can really adapt. Metabolic flexibility, some strategies that have been used in the past influence one of those, but you lose the flexibility of the other. So one example of that is actually low carbohydrate, high-fat diets.

When they're eaten chronically in the longer term, then you do increase the ability to burn fat as fuel very effectively, but it seems like the ability to burn carbohydrates as fuel is down-regulating. Even once your glycogen stores are full again. So even though you've got those carbohydrates in the muscle, you're not able to use them.

Your body has adapted to using fats or the enzymes for carbohydrate down-regulated. And so you just can't tap into that energy when you need to. 

[00:31:55] Jonathan Wolf: Do we know about how gut health fits into any of these discussions around exercise? Have there been any studies that look at these links and you know, is there anything you can share with us there?

[00:32:04] Dr. Javier Gonzalez: Yeah, I think it's a really exciting area. I think we don't know very much about it at the moment. What we do know is that if you just compare athletes with non-athletes, then they do have very different, gut microbiome profiles. It's difficult to disentangle, whether that is an effective exercise or an effective diet because most athletes are burning a lot of energy and eating a lot of energy. So the total volume of food is very high, but also the composition tends to differ as well from non-athletes. So it might be higher protein, potentially higher carbohydrates as well. And because of that higher volume of food, they're probably also getting more total fiber, more prebiotics as well. And so there are a number of reasons that could account for differences in the gut microbiome between athletes and non-athletes. I think the next step would really be to do randomized control trials of exercise, to see how that directly affects the gut microbiome, ideally with, and without weight loss. So you can then disentangle the effects of exercise from weight loss. 

[00:33:09] Jonathan Wolf: Whenever we're thinking about exercise, then I think we get a lot of questions about what should we eat sort of before, during, and after exercise. And I think there are a lot of myths here, right? You already answered right at the beginning. Like, do I need to have a protein shake if I'm doing an exercise I think you gave a pretty strong, no. So could you tell us a bit about what are the facts about sort of the requirements? And we don't always believe a lot about this idea of the sort of macronutrients at ZOE because there are so many different sorts of foods, but help us to understand What are the realities of this?

[00:33:42] Dr. Javier Gonzalez: Yeah. Well, one of the main roles of protein, or one of the reasons for taking protein, or at least eating protein in conjunction with exercise is to facilitate muscle reconditioning. And what I mean by that is the adaptation of muscle. So muscle is mainly comprised of protein, and we often think of the contractile protein. So the part of the muscle that produces force, the part that gives it the size and the bulk that you see in a bodybuilder. But actually, the proteins are also involved in the enzymes within the muscle, the mitochondria within the muscle, which are the kind of powerhouses of the muscle that produce the energy for cardio exercise.

And so protein is important in remodeling all of those different aspects of the muscles. So, I stand by the point that you don't need protein powders, protein itself is certainly important for both people who exercise and people who don't exercise. The reason I said no to protein powders is that you can achieve the same goal with dietary food sources of protein. And in many ways, they can actually be more effective than certain protein powders. So just to validate that if you compare, for example, a control condition where they might not have any protein at all, versus a soy-based protein versus whey, then what you tend to find over a training program is, the same amount of training that people will gain more muscle mass with the whey versus the soy and more muscle mass with the soy versus nothing. But what's really interesting is they had a fourth condition in this particular study that I'm referring to and it was milk. So just plain milk and it performed just as effectively as whey protein. 

[00:35:30] Jonathan Wolf: Amazing. So you don't have to eat something super artificial.

You could just, and I'm not suggesting everyone should eat milk because there's a big variation we see in response, but that's sort of quite amazing. And how much protein do you need? Because I think this is also an area where. Anywhere you go on like the grocery stores or anything, now here's this ultra-processed bar with a big label on it saying late high in protein, which obviously makes me think, oh, well, that's good.

I have that. And I have heard people say, oh, you must eat some vast amount of protein within 30 seconds of doing exercise or all that hard work is wasted, which I think if you're like me and you don't really love exercise, you know, you're doing it because it's important for your health. It's like, oh my God, I'm going to have wasted all that hard work if I don't get this protein in 30 seconds, like, I've always been a bit skeptical, but I bet there are real data on this, Javier. How do we think about that? 

[00:36:20] Dr. Javier Gonzalez: Yeah. So I guess before I tackle the dose point, I'll just talk to the timing point where it's one of those things where there's a grain of truth, but it's taken completely out of proportion where immediately after exercise, we are more sensitized to protein, and so if, for example, you have a pint of milk, which has about 20 grams of protein in, in the hours after exercise, more of that protein will be incorporated into your muscle. Then it would do if you hadn't exercised and it's still a relatively small amount. So of that 20 grams, it tends to be about two grams have been incorporated.

So about 10%. So exercise does sensitize the muscle. But that doesn't completely drop away within 30 minutes. It just gradually comes down over about 48 hours. So. Even 24 hours after exercise, your muscle is still sensitized to protein intake. More than it would be if you hadn't exercised. It's just slightly less than it would have done immediately after exercise.

So rather than a window, it's just a gradual decline in our sensitivity over a full 48 hours. 

[00:37:26] Jonathan Wolf: And so if I'm thinking, you know, I'm a listener I'm listening to this, does that mean I should be worrying about this, or actually if I'm eating a well-balanced meal with like plenty of plants, which we now have lots of different protein in them, and I'm not a super cyclist, am I going to get everything I need? Or is this something that I need to adjust to sort of compensating for? 

[00:37:48] Dr. Javier Gonzalez: Yeah, if you're eating three or more meals a day, you're probably eating in close enough proximity to your last exercise bout that you're getting a benefit. So you probably don't have to worry about it. If you're going to have exercise, and not eat for 10 hours then yeah, you probably want to fit some protein in between. 

[00:38:05] Jonathan Wolf: Got it. So if you're doing a sort of quiet very time-restricted eating, for example, I guess that would be a good example of one of the sorts of sustainable dietary patterns than potentially thinking about how exercise fits with that time window is something that given what you're saying, it sounds like you don't want it 12 hours away from when you eat equally well, it sounds like sometimes you might want to do the exercise before you eat. And other times you might want to be doing this shortly afterward, etc. 

[00:38:33] Dr. Javier Gonzalez: Exactly. Yeah. And it may actually be a case here for, there might be some scenarios. I'm not, I'm not completely against supplements. For example, I think they have a place and it's, it might be here where someone might be performing time-restricted feeding or intermittent fasting and not want to eat a lot of calories and a supplemental form of protein can then provide the protein without many calories. And so there's probably a scenario there where they can be useful. And I think the other scenario is for convenience as well. So yeah, I'm not completely against them. I just think you can achieve most of the goals, almost all of the goals with real food.

[00:39:10] Jonathan Wolf: Brilliant. And, you know, I think often the challenges, you can have a window thinking just about the exercise, but when you step back and look at the overall health impact, right, then we know so much now about the importance of sort of the quality of overall food. So I think figuring that out is interesting.

Now I have a question here, which is actually the reverse of this. How do I best fall for endurance exercise? So if I am doing some of this extreme exercise that you were talking about, how does that change this advice? If at all? 

[00:39:37] Dr. Javier Gonzalez: Yeah. This would definitely depend on the level of the athlete here. So if you take the tour de France cyclist. What you see in that diet would be viewed as pretty horrendous by most people in terms of the amount of sugar, for example, that's in it because they are burning through so much energy and sugar is such a good fuel for high-intensity prolonged exercise that the amount of sugar tour of France athletes gets through is actually incredible. So some of the reports in some studies have been up to half a kilo a day. Of pure sugar, which is incredible.

[00:40:16] Jonathan Wolf: Which I imagine you're not, you're not telling us to copy at home, kids. Is that right? 

[00:40:21] Dr. Javier Gonzalez: Absolutely not. This is one scenario where we treat them as a different species because in an hour they can burn through almost 2000 kilocalories of energy. Whereas your average person might be burning three, 400. So it's just a completely different ballpark. 

[00:40:37] Jonathan Wolf: I'm guessing that all these muscles that I'm using right now to keep my body upright while talking to you, it's not getting me to the 2000 and calorie output. 

 Okay. That's really helpful advice. So. One of the things we touched on at the beginning and which I'd really like to sort of talk about here at the end is personalization and differences. And I think you already said that you see differences between men and women, but that there were also other differences. Would you mind talking a bit more about that? I think both in general and then I think we'd love to talk a bit more specifically. One of these big changes that we see with women is obviously sort of before menopause, perimenopause, after menopause, what does the science say? And how should people think about that depending upon where they are as an individual?

[00:41:23] Dr. Javier Gonzalez: Yeah, I think it's a great question. It's one that commonly comes up when I give talks actually is, should women do their exercise differently to men, especially with this theme of whether they should exercise before or after eating, and, there's a bit of confusion as well, because, I think in some TV programs that have been shown over here, at least it was suggested that women respond very differently to men.

And it's true that women tend to burn more fat than men during exercise. So when we control for all of the important factors and we compare men and women, women tend to be able to burn about 13% more fat than men. But that's actually a relatively smaller difference compared to other factors. So if, for example, we look just within the group of men or within the group of women, then the difference between the highest and the lowest person is more than 300% difference.

So there are greater differences between individuals within each sex. Then there are between the sexes. So we've, we've done work on this and we're keen to do more work on it. The next step is to understand what are the factors that determined why one individual can burn a lot of fat versus another. And sex is probably one of those factors, but it's probably not a big one.

So I guess rather than, a fat oxidation gender gap, it's more of an agenda overlap in that regard. If we extend that to say menopause, then it does link because one of the main reasons we think women can burn more fat than men is the hormonal status of women. So estrogen and amazingly, they have done the studies where they've given men estrogen and immediately their fat oxidation increases.

And it probably also depends on the number of receptors women have to estrogens. Estrogen is a hormone that will stimulate a variety of responses, but it can only stimulate those responses when it binds to its receptor. And we've actually found that women with more of the receptors for estrogen show, a higher rate of fat oxidation.

So there's this complex interplay between the hormone, but also other aspects of the physiology of the person to actually get the response there. 

[00:43:35] Jonathan Wolf: So that's sort of the science showing you all these differences. If you're listening to this, trying to figure out what to do, and maybe let's take that example as a woman is I think a great example, which is something that we ended up talking a lot about, right?

Which is that your body is changing. And what worked for you when you were, you know, 35, maybe different. And this is true for men as well, but it's particularly true, we see with women because of this really big change around menopause. What should they be doing? How important is exercise around menopause? When one of the side effects we often see is weight loss, but I think there are also other implications that you've touched on, I think earlier to do with sort of bone density. How do we think about both exercise and diet, I guess, together through this period? 

[00:44:16] Dr. Javier Gonzalez: Yeah, those are the points I would mostly focus on in people who are considering how to mitigate the effects of menopause and, with the kind of strength, loss, and potential loss of bone mineral density. It's where strength training really comes into play. So ideally lifting relatively heavyweights, or it can be running as well. So you get a reasonable impact when you run much more than cycling. The forces that go through the ground when you hit that ground and through your leg and foot also stimulate bone growth and tendon strengthening.

So combining either weight training and or running with diets can really be the key there. So on the dietary front. It's probably four main areas I'd consider. One is calcium. So are you getting enough calcium in your diet? The second is vitamin D, which I know in America, in the US quite a lot of foods are fortified in the UK, not so much. So you might need to take a supplement there, especially if you don't live in a sunny climate. The third would be Omega 3 . So make sure you eat plenty of oily fish to get your omega 3. And the fourth would be adequate protein intake because we often actually forget that a lot of bone is actually comprised of protein as well.

And when we protein, one of the hormones that are released are known as GLP one which also stimulates bone growth as well. So those four dietary factors combined with some form of exercise that is going to load the bone are probably crucial there. 

[00:45:52] Jonathan Wolf: Javier, I think that's really fantastic and very actionable advice. I would like to maybe just sort of summarizing, what's been a very wide-ranging conversation and where I think there are many things that we haven't really had a chance to get into.

So I look forward to hopefully coming back to this in the future, I guess the starting point is this really rather surprising fact that exercise is not the key to weight loss. It's very important for your health, but actually on its own is not really going to transform your weight loss. That actual exercise starts at a lower level than I think many of us imagined.

So apparently I can do a brisk walk and I think you said 30 minutes a day was really going to have an impact on my health. And I didn't even have to do this all in one go. So I could actually have maybe like three pieces, which I think again is not at all what I think many of us understood. You then explain those actually two sorts of exercise and that this strength exercise, which is different from this longer-term, cardio are both important that the longer-term exercise, which I guess is your brisk walk through to running or cycling is great for our cardiovascular system and our blood pressure and trying to deal with heart disease, but actually a strength, exercise is very important. And if we want to stay strong long-term, and that can even mean so that we can continue to get in and out of a chair and things like this, then actually we need to do that because you painted this slightly depressing story that I think from about 35, we're all getting weaker and weaker and that therefore we sort of have to fight against it because you know, most of us are doing what I'm doing right now, which is sitting on a chair, talking and the good news is that apparently that burn some calories because I'm using some muscles, but it's not really enough to get me out of that chair in the future. Is that right, Javier? 

[00:47:48] Dr. Javier Gonzalez: That's correct. Yeah. Good summary. 

[00:47:50] Jonathan Wolf: And then I think we talked about these amazing studies that you have been doing and that you are recruiting for the next stage of looking at the impact of fasting on health.

And I think there's a very counter-intuitive discovery that actually, you know, doing exercise while fasted can actually improve some of your health outcomes and that for most of us the answer, isn't to only do this fasted at exercise, but actually a combination. And I think in general, one of your stories here is actually a sort of variation is important and this flexibility of your body is very important.

You taught us a bit about glycogen and why people hit the wall when they do the marathon. And that there's a lot of stuff that professional cyclists do for fun that we probably don't want to do at home. That as a result, they have these amazing gut bacteria. There's a different microbiome. And we think there's something really interesting, but this is really an area that is still very early. And then we talked about the food that you need to eat. If you're exercising, we understood that actually our muscles are mainly made of protein, which I guess explains why people talk about protein all the time and why we do need it. It's not just a marketing myth created by big food companies, but actually, there have been clinical studies where they've shown that if you drink a pint of milk, that works just as well as a fancy powder.

And that, although there is some scientific truth around this idea that, you know, in the hour after exercise, you're going to incorporate even more protein. Actually, if you're not a professional athlete, if you're eating three meals a day and those are sort of balanced meals with probably whole foods and proteins, you're fine.

If you are doing something like time-restricted eating, and you ended up with a very long period between exercise and food then actually potentially you should think again about that and either, maybe adjust a bit or even think about supplements, for example, with calcium. And then I think we finished with this fascinating stuff about personalization, where you said it's true that women on the average burn, I think you said 13% more fats than the man, which sounds like a really big difference it's related to estrogen. But when you go and look within the differences within women, for example, you're seeing this 300% variation, which is very similar to some of the things that we've seen in some of the big, ZOE predicts studies, looking at, you know, inflammation and things. So there's this huge variation within individuals. And so a one size fits all guide is going to have the same problems as everywhere else, but this does mean that as you go through menopause, there's a big change because of the change in hormones. And that's really some very specific things I think that you recommended. And let me see if I've got that right. So firstly, you're going to be losing strength. You're going to be losing bone mineral density. So you really need to think about that in addition to thinking about how your diet might need to shift because of the weight gain that may go with this. And so I think you're pushing in a particular here quite strongly that you need to think about strength conditioning. Can you be lifting quite heavyweights? Because I think you were explaining they need to be quite heavy to have that impact. Interestingly actually running is a form of strength conditioning, which I think will be a surprise for many people. And that on diet, you had some very specific recommendations.

So calcium, are you getting enough? Vitamin D, omega-3, and for people who are not vegan, then actually dairy-based products were a good solution there. And if you're not vegetarian, then sort of oily fish in terms of omega-3 and then added, making sure you're having adequate protein intake, where again, you said, you know, it's, you don't need to be doing some sort of special shake.

It's about understanding that you're eating a sort of balanced meal. That's got lots of protein. 

Javier, that's an amazing sort of tour across all of these things. I think that's really fantastic sort of actionable takeaway. Javier, thank you so much. I think that was so interesting. We enjoyed it very much.

And look forward to having you back in the future with the results of those new studies. 

[00:51:51] Dr. Javier Gonzalez: My pleasure, thanks for having me. 

[00:51:53] Jonathan Wolf: Thank you to Javier for joining me on ZOE science and nutrition today, we hope you enjoyed today's episode. If you did, please be sure to leave us a review and subscribe. If you're interested in learning more about ZOE and the best foods for your body, you can head to join and get 10% off your personalized nutrition program.

Finally, if this episode left you with questions, please send them in on Instagram or Facebook to ZOE. And we will try to answer them in a future episode as always. I'm your host, Jonathan Wolf, ZOE science and nutrition is produced by Fascinate Productions with support from Sharon Feder here at ZOE.

See you next time.