Does The Body Burn Fat or Muscle First?

Does The Body Burn Fat or Muscle First?

Whether their goal is to lose weight, build muscle, or sculpt your physique ... Nobody wants to lose muscle in the process. On the other hand, almost everyone on the planet is okay with losing some body fat if they have any to lose.

So, what happens to your body when you start shedding the extra weight? Does your body burn fat or muscle first?

Many of the top search results on the internet will tell you the answer is fat. They may also mislead you into thinking your body won’t burn muscle until carbs and fats are depleted.

Unfortunately, that's a misleading and oversimplified statement. That’s not what science has shown us for a long time.

The real answer is, it's complicated.

Yes, your body will burn fat before it starts breaking down significant amounts of muscle. But even that statement can be misleading if you don’t have the full context. 

There are a variety of factors involved, and it’s just not that simple. There are situations where you can actually lose a good amount of muscle in a short period of time.

If you want great results, this information will be really important to understand!

Whether or not your body burns more fat or muscle depends on several factors. Exercise intensity, workout duration, and your diet are all involved. That's only to name a few of the factors as well!

Let’s get into the details of how this all works, and I’ll cover how to minimize muscle loss along the way. There will be some science, but I will keep things simple and concise.

That way, you'll know exactly how your body treats muscle and body fat when it comes to losing weight. If you approach weight loss the right way, you can preserve a lot more muscle and see excellent results!

Does Your Body Burn Fat or Muscle First: Where Your Energy Comes From

To understand how your body burns fat and muscle, you have to understand how your body uses energy. So let’s start with the body’s energy hierarchy.

The body's energy hierarchy is a well-organized system. It's designed to use what is most efficient to meet the body's energy demands. Simply put, the body has to prioritize how much of and when to use each energy source it has available.

The body's primary energy source is carbohydrates. If they’re available, generally that’s what it will use first. Basically, all carbohydrates are broken down into glucose. This is a simple sugar that can quickly and easily be used for energy. 

Glucose is essential for bodily functions like brain function and muscle contraction. The good thing is, it doesn’t take very long to digest carbs and enter the bloodstream.

When your blood sugar is high, insulin pulls the extra sugar into tissues like your muscles. These stored carbs in your muscles are called glycogen. 

When you exercise at high intensities, your body uses that stored glycogen for energy. It doesn't take long to break it down and use it, so it's the first energy source your body goes to in this case.

Here’s the kicker though … You’re actually using fat, carbs, and protein (amino acids) for energy all the time (1)(2). We just use them in different ratios depending on how quickly we need energy.

Allow me to explain.

Fat is a dense energy source, and it can last a lot longer than carbs or protein can. 

An average person likely has enough glycogen for up to 100 minutes of marathon running (3). The amount of fat they have on average could last 5 days at the same intensity (3). 

While fat can provide energy for longer, it also takes longer to break down and produce energy (4). It must also be at a low enough intensity that oxygen is readily available. 

That’s called aerobic exercise, which means with oxygen. When you exercise at very high intensities, it’s called anaerobic exercise. This actually means without oxygen, but it's not exactly what it sounds like. 

Obviously you’re still breathing oxygen, but you get out of breath right? At those high intensities, you use oxygen faster than you can breathe it in.

Your body can and will use fat for energy in high amounts, but only under low-intensity conditions. During these times carbs and protein are still being used, but in lower amounts.

During high-intensity exercise, fat utilization will be lower, and carb utilization will be higher. Protein will get used as well, but only 5-10% of the total energy used will come from it.

Now, if you’re low on carbs and you keep increasing your exercise intensity, your body generally can’t break down fat fast enough. In that case, you may break down more muscle for fuel than you normally would.

So what I’m saying is that your body would rather use carbs and fats, but it will still break down muscle for energy too. They happen at the same time whether in small or large amounts.

So when you ask, “Does fat or muscle burn first?” The premise of the question is flawed. 

It’s not about what happens first. A better question is, “How can you minimize the inevitable loss of muscle as you lose weight.”

In the next section, I’m going to cover why people lose muscle when they diet. Then we'll talk about how to prevent muscle loss when you're losing weight. It’s really fascinating stuff to understand!

Why Do People Lose Muscle While Dieting?

Let’s back up a second, and start with how to lose weight in the first place.

So, how do people lose weight? Well, the answer is simple: You must burn more calories than you consume.

The first law of thermodynamics states that energy cannot be created, nor destroyed. So, when your body uses energy, it has to come from something you’ve consumed at one time or another.

Your body burns a certain amount of calories each day and you consume a certain amount. If you consume more calories than you burn, your body will have to store the extra energy somewhere.

This can be in the form of stored fat. It could also be carbs in the form of glycogen. It could also be protein in the form of muscle tissue.

When you are dieting because you want to lose weight, you must consume less calories than you are burning. That way, the excess energy you use must come from somewhere that was previously stored in the body.

Ideally, it would all come from body fat, but that won’t ever be the case. There will always be some degree of muscle loss.

This could be for a few reasons.

1. Your Body Is Designed to Survive At All Costs

Your body is the ultimate survival mechanism. In fact, that's actually the reason we have body fat; body fat is extra calories to survive off of in case of famine.

Your muscle tissue burns calories 24 hours a day, and the body knows this. So, when you give yourself less energy than you use, your body may lose muscle to lower your energy usage. 

The less energy you burn, the longer you’ll potentially survive when food is scarce. When you eat in a calorie deficit, your body doesn’t know you’re doing it on purpose.

2. Your Body Doesn't Think You Need As Much Muscle When You Lose Weight

Your muscles are designed to move your body. The heavier you are, whether from muscle or fat, the more muscle you need to carry that weight. Believe it or not, very overweight people have quite a bit of muscle to carry themselves around.

As you lose weight, your body sees the extra muscle as unnecessary. If your body doesn’t need it, it doesn’t want it.

3. You May Not Be Eating Enough Protein

Your body breaks down muscle tissue for multiple reasons. During exercise, some of it is broken down for energy. When you’re sick, your body may also break down muscle for glutamine (5). 

Your immune system uses glutamine for many of its processes. So when glutamine is running low, and your immune system needs it, muscle tissue will get broken down.

If you don’t consume enough quality protein, you aren’t giving your body what it needs to replenish what was lost. Under-eating protein is an easy way to lose muscle over time.

This is especially true when you’re dieting!

If you are losing muscle when losing weight, it doesn’t have to be for only one of these reasons. It’s likely a combination of all 3!

Now that you understand how this works, let’s cover how to minimize muscle loss.

How to Minimize Muscle Loss

There are multiple strategies to preserve lean muscle while you lose body fat. You just have to make these a priority.

Unfortuntely, there is no way to completely prevent muscle loss. But with that being said, these strategies will help you hold onto as much as you can!

Get Enough Protein

Your muscles are the largest reservoir of protein in the body. When your body needs protein, it will break down your muscle tissue. Eating adequate amounts of protein daily is crucial to reduce the amount of muscle lost (6).

How much protein do you need to minimize this loss? Studies show that 2.3g of protein per kg body weight is enough to minimize muscle loss when losing weight (7). This is just over 1 gram of protein per pound of body weight.

This is a rule of thumb I always use when I'm looking to lose weight and cut body fat!

Prioritize Resistance Training

Remember when I said as you lose weight your body doesn’t think it needs to hold onto that extra muscle? Well, every time you lift weights your muscles are being challenged. This sends signals to your body that you need that muscle.

Heck, you might even build a little muscle along the way if you do it right!

Monitor Your Calorie Deficit

While it's necessary to create a calorie deficit for fat loss, you don’t want to drop your calories too low. Rapid weight loss can lead to faster muscle loss for the 3 reasons I mentioned in the last section.

Gradual and sustainable weight loss is the key to success without losing too much muscle.

Get Enough Rest and Recovery

Aim for 7-9 hours of restorative sleep each night to support your body's recovery and repair processes. Otherwise, you risk elevating cortisol levels (8), which can lead to muscle breakdown (9).

Maximize Your Fitness Results with 1st Phorm

So, if you paid attention you now know the answer to the question: “Does your body burn fat or muscle first?”

Your body is burning fat, breaking down muscle, and using carbs for energy. This is happening 100% of the time every single day. Your body is just a master at shifting which fuel is being used more or less at which times.

When it comes to losing weight, everyone wants to burn fat, and nobody wants to lose muscle. At least, I haven't met anybody who thinks differently!

The more muscle you have, the more calories you can burn every day. So even if you want to be lean, holding onto more muscle is advantageous. Muscle tissue won't only help you lose body fat in the first place, but also keep it off!

Now, if you want to keep muscle while burning off unwanted fat, you need to exercise. No, I don’t mean go for a run, although that’s still great exercise that can help you burn fat. 

The exercise I’m referring to is lifting weights regularly. However, this can also be any form of resistance training that puts enough stress on your muscles. Without this kind of training, you will likely lose more muscle. That's just the truth.

You also should prioritize quality sleep to minimize muscle loss. But, above all else, your diet is the most crucial! If you don’t eat enough protein, and/or enough calories, it will be a major struggle to keep muscle.

This is the area most people have trouble with. I get it too ... Not everyone studies nutrition and has a good understanding of how to eat effectively to reach their goals.

It can also be hard to find the right answers online too. Oftentimes, you'll get bad or conflicting information, making it hard to know the facts.

That’s where we can help you! We’ve developed the most complete all-in-one health and fitness app to help you succeed: The 1st Phorm App.

Inside the app, you get access to your own expert advisor to teach you, coach you, and hold you accountable. You can message them anytime, and they’ll give you the information you need.

You also get access to a full library of workout programs, a custom nutrition plan, and much more. The 1st Phorm App simplifies the process of earning results so you can reach your goals!

Just know we're also here to help you with any questions you may have. You can talk to one of our NASM Certified Personal Trainers and Nutrition Coaches any day from 6 AM to 10 PM Central. Send us an email at or give us a call at 1-800-409-9732.

If you're ready to get some incredible results, just download the 1st Phorm App today!

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(8) Hirotsu C, Tufik S, Andersen ML. Interactions between sleep, stress, and metabolism: From physiological to pathological conditions. Sleep Sci. 2015 Nov;8(3):143-52. doi: 10.1016/j.slsci.2015.09.002. Epub 2015 Sep 28. PMID: 26779321; PMCID: PMC4688585.

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