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Has your progress stalled, or are you experiencing unexplained fatigue? It could be low energy availability.

As we strive to push our physical limits, sometimes we might inadvertently fall into the trap of Low Energy Availability. 

This can lead to a condition known as Relative Energy Deficiency in Sport (RED-S) which can severely hinder not just our performance but overall health.

In this episode, I’ll dissect the science behind low energy availability and RED-S, and help you understand how you might be underfeeding your body despite intense training routines. You will learn about the symptoms of RED-S, its consequences, and how to prevent it.

So tune in and learn how to balance your diet with your exercise and training and why it’s essential to match your food intake with your energy expenditure.


0:00 – Please leave a review of the show wherever you listen to podcasts and make sure to subscribe!

1:24 – What is low energy availability?

4:14 – What is your energy availability and how do we calculate it?

8:03 – Try Triumph today! Go to and use coupon code MUSCLE to save 20% or get double reward points!

18:21 – What would happen if you maintain a low energy availability for too long? What are RED-S symptoms?

Mentioned on the Show:

Try Triumph today! Go to and use coupon code MUSCLE to save 20% or get double reward points!

What did you think of this episode? Have anything else to share? Let me know in the comments below!


Hello, hello, and welcome to Muscle for Life. I am Mike Matthews. Thank you for joining me today for a new episode on the subject of energy availability. Something that many fitness educators don’t talk about but is very relevant to everyday gym goers. If an expert talks about energy availability, particularly low energy availability, Which is going to be the focus of this episode.

They are usually talking about high level athletes, people doing a lot of exercise and a lot of training because those are the people who are most likely to experience low energy availability. But there is one scenario where everyday gym goers like you and me, can experience symptoms related to low energy availability.

And that is when we are cutting and if we don’t know what to do about it, we can make the process of losing body fat a lot more difficult than it needs to be. And so, In this episode, you are going to learn about energy availability, particularly low energy availability. What does that mean? How do you figure out how many calories you should be eating, especially when cutting to avoid low energy availability?

And I’m going to also explain why you want to avoid low energy availability. What happens when it goes unchecked and more? Okay, so let’s start this discussion as I normally do with a, a simple definition of terms here. So, energy availability, what is that? Well, that simply refers to the amount of energy that the body has remaining to perform various functions after you subtract the energy that you are burning during exercise.

And so then low energy availability describes a situation where your body doesn’t have enough energy to maintain optimal health and performance because. You have burned too much energy through exercise, or you haven’t eaten enough food or a combination of both. Now, this low energy availability state is fairly common among athletes, particularly those who manipulate their body weight for competition or for whom leanness or lightness is preferable, like wrestlers and martial artists, bodybuilders, gymnasts, ballerinas, long distance runners, jumpers, and so forth.

And this occurs with these. People fairly often because they are typically limiting their food intake and doing a lot of training. Low energy availability isn’t only an issue among athletes, though research shows that it can occur among people who are new to training and in my experience, working with many people over the years.

This has been more commonly seen among people who start on the lighter side. So skinny guys, skinny women who start training fairly intensely. Let’s say they go from no strength training to four or five hours of strength training per week, and maybe more steps as well. So even more calories and more activity, which is great, but.

These people often don’t have big appetites to begin with. They often are not eating very much food to begin with, and they often don’t start eating more food with all the exercise. And so their body already is starting out in not a low energy availability state, but closer to that state than the average person.

And then they start doing a bunch of training without eating more food, and it can push them into that low energy availability. State now studies show that low energy availability can also occur when people are trying to lose weight. And in the same way they go from not much physical activity to a lot of physical activity and not a lot of food.

And it also can occur in people with an eating disorder such as anorexia nervosa, and if you fail to address this low energy availability. Problem. It can develop into a bigger problem called relative energy deficiency in Sport Reds or R E D Ss. But reds is at least how I read that, and this is a syndrome that affects many aspects of physiological function.

It’s something that you want to make sure that you avoid. Now, how do you avoid it and how do you avoid even low energy availability? Well, the first thing you want to know is your energy availability. And to calculate that, you can use a pretty simple equation. You have your total daily energy intake, so let’s say over a 24 hour period, total calories eaten, and then you subtract out the total amount of calories burned during exercise, and then you divide that number by.

Your fat-free mass in kilograms and fat-free mass, by the way, refers to your total body weight minus the weight of your body. That’s fat. So that’s your muscle, of course, but also bones and organs and water and so forth. And if you are not sure how to calculate that, you can head over to legion

Go to learn in the menu, then go to tools. And go to body fat percentage calculator, and you can use that to approximate your body fat percentage. It’s not going to be perfectly accurate, but it’ll be close enough for our purposes here. Good enough for government work, as they say. And with that, you’ll also get the approximate amount of lean body mass, which is synonymous with fat free mass, as well as fat mass.

So you use this equation, you put in your numbers, and then you get your energy availability expressed as calories per kilogram of fat-free mass per day. And if we look at research on the matter, just to give us some context of. What is high? What is low? Most scientists agree that something around 45 calories per kilogram of fat-free mass per day is optimal for health.

And if we get below 30 calories per kilogram of fat-free mass per day, we are now entering low energy. Territory. And to help you understand this, let’s walk through a simple example. We have Joe. Joe weighs 80 kilograms, so about a hundred and seventy five, a hundred seventy six pounds. He has 12% body fat.

Therefore, Joe has about 70 kilograms of fat-free mass. He also eats, let’s say, 3000 calories per day. He’s pretty active. He burns 400 calories during his daily workouts. Now he burns more calories through physical activity. Like walking and doing other simple daily tasks. But as far as vigorous physical training, it’s about 400 calories per day.

Therefore, his body has about 2,600 calories per day to do all of the various things that it needs to do. And so if we take those numbers and we plug them into the equation that I shared with you, we get Joe’s energy availability. Relative to his fat-free mass. So we have 3000 calories eaten per day, minus the 400 calories per day of exercise, energy expenditure.

And then we divide that by the 70 kilograms of lean mass, lean body mass, fat-free mass that he has. And that comes out to about 37. Calories per kilogram of fat-free mass per day. And based on that and the research that I just shared with you, Joe is in a state of adequate energy availability, but it may not be optimal for long-term health.

If he could increase his calories to about 3,500 per day and keep his workouts the same, that would bump ’em up to about 44 calories per kilogram of fat-free mass per day, which is probably going to be better for his long-term health as well as his physical performance. Now, let’s say Joe wants to cut, he wants to get ready for a photo shoot, so he slashes his calories to 2000 per day.

Well, that would drop his energy availability to about 23 calories per kilogram of fat-free mass per day. And while that isn’t necessarily harm, there’s no long-term harm in doing that. If it’s for a shorter period of time, let’s say it’s several weeks, maybe even upward of two months, if Joe were to consistently eat something around 2000 calories per day for too long, he would start to develop symptoms associated with reds, which I’m going to talk more about in a minute.

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Now if you are playing around with your numbers and you’re surprised at how much food you quote unquote, should be eating to maintain optimal health, I understand it. It is a pretty big number for most of us. Now, that doesn’t mean that you have to work out how you’re going to eat 45 calories per kilogram of fat-free mass per day.

But if you are down somewhere in the twenties, you should look at how you’re going to get that up. And that may mean doing a phase of lean bulking, which isn’t a bad idea if you haven’t done it in a long time. And if you have stayed pretty lean for a long time and you have aired on the side of eating less rather than more.

And if your energy availability has. Spend somewhere in the twenties or maybe the low thirties at best for a long time. Now, this is also why many evidence-based sports coaches don’t recommend that athletes try to get and stay really shredded, try to maintain really low levels of body fat. Now, there are some exceptions, some sports that require very low body weights, which inevitably means low body fat levels because you don’t want to have.

Low muscle levels like no muscle and just fat, and a low body weight. Now you want it the other way around. Even if you don’t weigh a lot, you do want to still have a fair amount of muscle, as much as you can have at whatever weight you need to maintain. And then not a lot of body fat, but in most cases, athletes are recommended to maintain an athletic body composition, but not a shredded.

Body composition. For instance, men are usually not advised to go below 10% body fat, or at least not explicitly set up their diet to get them below 10% body fat and keep them there. In some cases, there’s so much training, it’s almost impossible to eat enough food to be above 10% body fat. Think of like a cyclist, for example, or a swimmer.

At any rate, many other male athletes have reported that. They seem to perform best at between 12 and let’s say 15% body fat. So again, an athletic body composition, but not a shredded body composition. And in that range, many male athletes report that they have a lot of energy, they have a lot of strength, a lot of power, but they don’t have so much body fat that they feel weighed down by it and their joints aren’t taking an extra beating because of all of the excess body fat and so forth.

And in women, it is usually not advised for. Female athletes to try to maintain anything lower than probably 18 to 20% body fat and many female athletes find that they experience their best performance with a little bit more body fat than that. Probably something closer to 23 to 25%. In both cases, men and women, it’s not just the additional body fat that is making them perform better.

That is a factor because of some of the hormonal benefits that you experience when you go from low levels of body fat to a little bit more body fat. Like when you’re a guy and you go from seven 8% body fat to 12, 13% body fat, that is going to enhance your hormone profile. And the same thing goes for women.

So that is a factor, but in. Equal factor. And probably a bigger factor is simply the fact that they can eat more food at those higher body fat levels, and it can be a lot more food, hundreds and hundreds of additional calories every day, and their bodies need those additional calories. They need that high energy availability to perform well in their workouts and in their competitions, and also to recover from all of the training.

Now, for those of us who are not, Professional athletes. We don’t have to manage our calories as meticulously as we would want to if we were professional athletes, but it is smart to keep energy availability in mind to keep the information you’re learning in this podcast in mind, and particularly when you are in a maintenance phase, if you’re in a lean bulking phase.

You are not gonna have a problem with energy availability. When you’re cutting. You are gonna have a problem with energy availability, but you can’t get around that. That’s okay. That’s, uh, that’s baked into the cake as they say. You just don’t wanna be cutting forever. Remember that a calorie deficit is a fat loss intervention.

It’s not a lifestyle. And so then when you are in maintenance phases, which can last for a long time, especially if you’re someone like me who has been training for a while, who has gained a lot of muscle, who is happy with their physique and is mostly just trying to maintain it. You want to ensure that your energy availability isn’t generally too low.

You want it to be consistently sufficient. And what I’ve found in my experience with my own body and working with a lot of people over the years, a maintenance caloric intake of something around, let’s say at least 35 in the range of 35 to 40. Calories per kilogram of fat-free mass per day seems to work well.

If you exceed that, that’s fine, but for most people, that is now going to turn into a lean bulking phase, not a maintenance phase. So for example, I have about 181 or 182 pounds of. Fat-free mass, so we’ll say 82 kilograms multiplied by 40, so that’d be calories per kilogram of fat-free mass per day. That gives me about 3,300 calories, and I burn probably about 3000 calories per day on average, maybe 3,100.

And so 3,300 would be great for Lean bulking. That would be about a 10% surplus for me, which is exactly what I’ve done in the past. That’s where I would generally start my lean bulking phases, usually 33, 3400, and that would work for. A month or two, and then I’d have to start increasing my calories.

Usually every four weeks, I’d have to increase by about another hundred calories just to keep gaining weight and keep gaining strength. And again, if you’ve never done that before, I highly recommend that you do it and you will experience firsthand how great it is to have a a higher energy availability.

You’re gonna have a lot of energy in your workouts. You are going to be a lot less fatigued in your workouts. You are going to sleep better, you are going to recover better. It can be pretty marked. However, the surplus does come with fat gain. And so in my case, if I were to increase my calories to 40 calories per kilogram of fat free mass per day, I would experience some of those benefits.

I would gain a bit of body fat and then eventually I would stop gaining body fat. My body would normalize, and there are various reasons for why that happens, and it comes down to just. More activity, physical activity, not exercise per se, but it’s even just more spontaneous activity, and that’s just part of our body’s homeostatic mechanisms to maintain things the way they are.

That applies to body composition. It generally wants to keep our body composition the way that it currently is. And so if I were to increase my calories to 40 per kilogram of fat-free mass per day, I would. Experience some benefits. I also would get fatter and then I would stop gaining fat. And if I were to just keep eating though, let’s say 3,300 calories per day, then I would maintain that higher level of energy availability, also that higher body fat level, and I would continue to experience those benefits and.

And that’s perfectly fine and great, but I like to be a bit leaner than that. I like the body composition that I maintain around 2,800 to 3000 calories per day, and that’s not so little to cause issues related to low energy availability. I. But it would not be optimal if I wanted to maximize my physical performance, if I wanted to get as strong as I possibly could, or if I wanted to get into a sport and be able to perform as well as I possibly could.

Okay, so now let’s talk about what can happen if you maintain low energy availability for too long. So earlier I mentioned this relative energy deficiency in sport. Reds and the most common reds symptoms include reduced training capacity, repeated injury or illness, prolonged recovery times, poor mood, poor sleep, failure to lose weight, reduced sex drive, cessation, or disruption of the menstrual cycle, and excessive fatigue.

As you can gather from those symptoms, reds is disrupting some pretty important physiological systems. Like for example, it disrupts the hypothalmic pituitary gonadal axis, sometimes called the H P G axis, which regulates sex hormones like estrogen and testosterone. Low energy availability also can alter thyroid function.

It can cause changes in appetite regulating hormones, including decreasing lept. And oxytocin. And increasing ghrelin and peptide. Yy and adiponectin, which can greatly increase hunger and cravings and make those things resistant to eating where you eat food, a substantial amount of food even, and you’re still hungry and you still have cravings.

Low energy availability can also reduce insulin and insulin like growth factor one levels. It can increase growth, hormone resistance, it can elevate cortisol levels. And because of other hormonal changes in women’s bodies, it can disrupt menstrual function and even stop the menstrual cycle. And then there are other hormonal changes that relate to bone health, that can lower bone density and can disrupt bone metabolism.

Research also shows that low energy availability when it becomes exacerbated, can reduce metabolic rate. And that’s probably so your body can conserve energy for more vital functions. And this is also probably why studies show that low energy availability is associated with an increased body fat percentage and increased muscle breakdown rates.

And while it might seem paradoxical to. Increased body fat percentage in such a situation where you have somebody who’s already pretty light and they don’t eat very much food. Research shows that it can happen. You can have somebody who’s losing muscle and replacing that weight with body fat. So they’re maintaining more or less.

The same body weight, but a body decomposition is occurring, so to speak. A, a number of studies have reported it, including ones that were conducted with people with anorexia. As you can imagine, low energy availability and impairs immune function. And one study, for example, researchers found that elite runners who were likely suffering from low energy availability were experiencing more upper respiratory tract infections.

So they had sore throats, headaches, runny noses, coughing, fever, then. Elite runners who are not energy deficient. Mental health and function is impacted by energy availability because research shows that people with low energy availability have decreased cognitive ability. They have decreased attention.

They are at an increased risk of anxiety and depression. For example, in a study that was published in the British Journal of Sports Medicine, researchers found that people admitted to hospital with sports related injuries and low energy availability. Were f. 4.3 times more likely to report impaired judgment.

1.6 times more likely to report feeling uncoordinated and twice as likely to report problems concentrating than people who are admitted with adequate energy availability. And lastly, of course, reds can also impair physical performance. Research suggests that it can hamper strength, endurance reaction, time, speed recovery.

It also impairs muscle protein synthesis. Which makes training less effective, strength training, any sort of resistance training, less effective, it gets in the way of building muscle. And given those factors, it’s not surprising. Then that research shows that athletes who likely have the lowest energy availability tend to be the ones who perform the worst in their competitions.

And so those are just a few of the reasons you should pay attention to your calories. Make sure that they are generally sufficient. Make sure that generally you have plenty of energy available or your body has plenty of energy available to it. Don’t, for example, do this. Don’t eat very little food throughout the week so then you can eat a lot of food and drink a lot of alcohol on the weekends.

I’ve seen people I know personally do this. I’ve heard. From many people over the years who have done this to try to maintain what they consider an acceptable level of body fatness while still being able to basically binge eat and binge drink a couple of days per week, and maybe they don’t do it. Every week, but they’re doing it at least a couple weekends per month, and it can work for a time in that they can undo the damage of the weekend.

So on the weekend, let’s say they gain a couple of pounds of fat, and then they severely restrict their calories throughout the week and they lose a couple of pounds of fat. And then the following weekend, okay, they are back to square one. But what they don’t realize is when they are consistently in a low energy availability state, when four, five days out of the week, their calories are very low, the two or three days of higher calories are not enough to dig them out of the.

Hole that they’ve started to dig toward reds. And if they keep this pattern up for long enough, they will start to experience some of the symptoms, if not many of the symptoms that I just mentioned. And so then what you want to do is the opposite of that. You want to generally be in a state of sufficient energy availability.

Again, anything, let’s say 35 to. 40 calories per kilogram of fat free mass per day seems to work well for most people. And occasionally, maybe you do need to go below that because you want to cut for a bit and get leaner, and that’s fine. And occasionally maybe you go above that because you want to lean bulk.

You want to maximize muscle and strength gain. Or as I mentioned earlier, you’ve never done it before and you want to experience what that higher level of. Energy availability feels like. For example, I have spoken to many women over the years who got into strength training, a bit overweight, and then they lose the fat and they’re super happy with their physique, and then they are very resistant to lean bulking because they’re very happy with their physique and they don’t want to intentionally gain fat and they don’t want to go backward, is kind of how they perceive it.

In some cases, I’ve been able to coax them into trying a lean bulking phase anyway, and just accepting a little bit of fat gain and also understanding that they know how to lose fat. Now, they’re never going to struggle with their body composition or their body fatness like. In the past, things are very different now, and so then after doing it for a bit, many have reported back to me how amazing it is and how much better they feel physically and mentally, and how great their workouts are and how much progress they’re making.

It’s pretty fun if you’ve never done it before, and especially if you have stayed lean for a long time. Well, I hope you liked this episode. I hope you found it helpful, and if you did subscribe to the show because it makes sure that you don’t miss new episodes. And it also helps me because it increases the rankings of the show a little bit, which of course then makes it a little bit more easily found by other people who may like it just as much as you.

And if you didn’t like something about this episode or about the show in general, or if you have. Uh, ideas or suggestions or just feedback to share? Shoot me an email, [email protected], muscle f o r and let me know what I could do better or just, uh, what your thoughts are about maybe what you’d like to see me do in the future.

I read everything myself. I’m always looking for new ideas and constructive feedback. So thanks again for listening to this episode, and I hope to hear from you soon.

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