top of page

Why You Can't Actually Build Muscle And Burn Fat At The Same Time

I'm really into fitness if you can't tell. So I am bombarded with lots of information about building muscle and losing fat at the same time. Since I'm a dietitian I know that , it's actually not true. Here's why you can't actually build muscle and burn fat at the same time.

Don't want to read a ton? Scroll to the bottom to get the takeaways :).

First Burning Fat and Building Muscle are 2 Separate Goals.

Sorry to get black and white here, but it must be done to keep this post as simple as possible when in reality physiology is complex!

Let's start with good ol' definitions since I'm a definition girl. I like to be clear and concise because ambiguity in nutrition and fitness is where I think we go wrong.

Catabolism- breaking things down.

Anabolism- building things up.

Metabolism- catabolism + anabolism at the same time.

Wait, I thought you couldn't break things down and build things up at the same time.

Well, you can but if you do you have what is called maintenance.

If you have a goal to build muscle, or to lose fat it means you don't want to maintain. And therefore, you want to do more of 1 or the other.

What I'm talking about is the energy balance equation. Which, yes there are many many factors that go into play there too but to keep it simple:

Calories are units of energy.

Calories are used to build things in our body : amino acids build into proteins , essential fatty acids build into lipids. Lipid is another word for fat but its not only adipose. Fat in our bodies is in our brains and every single cell membrane. Every. single. cell. membrane.

When more energy is given to our bodies, that means they can build more things. If the body feels it is getting more energy than it needs it will store it.

When our bodies want more energy than it is given then it will find it. It will break things down- like proteins and fats and glycogen so it can maintain the system (thats you, you're the system).

So in order to have a goal to build muscle it needs to be separate from losing fat. They are two separate goals. They have 2 separate requirements. They require 2 different amounts of energy.

Second, To Burn Fat means to BREAK DOWN.

Burn fat- that is called beta-oxidation in biochemistry. It means that lipids enter into a system where they are "oxidized" or "burned" to provide power. When we are at rest, we burn mostly fat. Why?

Because it takes a long time to remove every carbon form the fatty acid chain of a fat. Haha, sorry if I lost you there.

So I'll repeat in a different way. It is a slower process to breakdown a chain of fat and thats why it is the ideal source of fuel when we are just chillin. Me, right now, sitting at my desk writing this? My body is preferring the use of stored fat.

My fat is also being replaced. I just ate an Oatmega bar so that provided calories or energy from fats, carbs and proteins.

If my goal is to "burn fat" then I'm going to keep my energy intake BELOW my bodies needs so that the fat isn't replaced. This won't be an instant change overnight. I have to constantly be eating fewer calories than my body needs in order to lose fat. If I want to do that.

That's why if your goal is to lose fat you must be in a calorie deficit.

In other words, you have to eat fewer calories than you require. If I'm working with someone who has a fat loss goal, and after my assessment I feel it is appropriate, then I get to dietitian work! I identify the caloric needs, and I make some adjustments to shift the body into relying more on its own stores than that it is being fed.

Also, this isn't a simple google task. I spend a lot of time playing around with numbers so that way ALL of them make sense. I digress.

Anywhoo the take away- want to "lose fat" then be in a calorie deficit. And in this calorie deficit expect these things to happen:

Low energy, because you are literally giving your body low energy.

More fatigue, again because of your low energy intake state.

Not being as strong or as fast in the gym, at least not over time.

Feeling hungrier than normal.

Thinking about food more because you're actively trying to eat less.

Also, don't expect to build muscle because to do that you need to eat more calories than your body needs to maintain. And here we go into that ...

Third, To Build Muscle means to GROW

Okay, so everything I said about fat above you can except the opposite here.

To build muscle the body needs to use energy to build. Specifically, it needs enough energy to build amino acids into protein and protein into muscle fibers.

Think about a construction worker building a house. Imagine if the construction worker was not eating? Can the worker build the house? No.

Also, we can't forget that to build muscle muscle needs to be OVERLOADED. That doesn't involve the kitchen. That happens in the gym. You have to pick up heavier weights. When you think to grab 12s you need to grabs 15s. When you think you want to squat 50 pounds you really should squat like 100 *.

*Please don't take my numbers here as rules. Im throwing 'em out there as hypothetical situations. You are you're own you. You need different weights to overload your muscles.

So back to nutrition.

When you want to build muscle, you overload them at the gym. That means you need to haver enough energy to be able to do that, and not just physically do that but mentally do it.

I can't tell you how many times I've gone into the gym, and mentally just wasn't willing to pick up heavy dumbbells. I was low energy. That happens, it's to be expected if youre low on fuel.

When I increase my calories, especially calories from carbohydrates, I mentally and physically can lift the weight.

Why also physically? Because the preferred fuel source here for explosive quick movements is glycogen.

Our bodies are like whoa! You're active right now I need this fuel quick. I can break down glycogen pretty fast. That's why its important to not only get enough calories but enough calories from carbohydrates.

In order to build muscle you have to be in a surplus of energy so that you have enough energy to lift the weight required to overload the muscle and to then repair and build bigger tissues.

Okay, but wait. You have probably seen and heard maybe experience yourself getting stronger in the gym but also seeing more muscles. Well, you're probably losing more fat OR your gaining more muscle. But both aren't really happening at the same time.

I've seen some videos where people show their body scan results. And what do you see? They built muscle and they lost fat since their last scan.


What they don't show you is the weeks, probably months of phases their bodies went through and that their coach put them through.

When you start a workout program, it usually begins with a muscle building phase, then it turns into a fat burning phase. So that's why these programs say you can "build muscle and lose fat".

What they really should say is "Build muscle (in the beginning weeks of this program and then ) Lose fat" (at the end when we put your body under high calorie burning workouts, add cardio and lower your food intake). "But also change the way you eat during each phase so you can achieve those goals."

So together the workout program should read:

Build Muscles in the beginning and then work on losing fat but make sure you change your nutrition while you change your workout routine.

And hire a dietiti