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How to Exercise on a Diet Without Losing Muscle

Sam Biesack | BS Behavioral Neuroscience, MS Exercise & Nutrition Science, CSCS

April 16, 2018


We always talk about “losing” when it comes to body fat. We want to burn, tighten, and see that number on the scale go down.

If that was all that mattered, all you’d need is a calorie deficit: eat less until you get skinnier. Simple. But that’s not all that matters, which is why we care about macros (especially protein) and why we need to exercise when we lose weight.

Because trimming up our bodies isn’t just about losing the bad, it’s about keeping the good. “The good” is muscle, lean body mass, or everything that isn’t fat. And while exercise shouldn’t be relied on to drive fat loss, it is a part of any smart plan to lose fat while maintaining muscle. This article will show you how to do that.


Find Weights, Lift Them

Exercise doesn’t (or shouldn’t) drive your fat loss. That’s nutrition’s kingdom. Instead, exercise is a tool to help keep muscle onboard as you start your controlled descent into Leansville.

And we need to make something clear: cardio doesn’t do the trick. Yes, cardio (which we’ll talk more about later) has its place in a fat loss journey, but it isn’t good at maintaining muscle. No—in the court of fat loss, nutrition is king and resistance training is his queen. Cardio is probably the sad jester.

(Obviously, there’s more to it than this, so check out our article on the “weights vs. cardio” debate.)

Lifting weights stimulates muscle growth when you’re in maintenance or a surplus, but it can also stimulate muscle retention when calories are restricted. So, to keep it short and sweet:

How hard? That’s the next section…


Training Volume—Where to Start

“Training volume” is a fancy term for “how much work you do when you exercise.” In terms of lifting weights, this is technically the sets x reps x weight lifted for every exercise you do. If you’re just starting to resistance train, then this doesn’t have to be that complicated. You can start with 2-3 sets of each exercise, hit each muscle group, and train 2-3 times per week. This is a great, simple place to start, and you’ll find that you progress quickly from there. As a beginner, you might even find you can grow some muscle while losing fat—which is the holy grail of dieting!

For more on how to train to stimulate muscle growth and retention, check out our two-part series on programming for muscle gain.

If you’ve already been hitting the gym, the temptation will be to make a big change. I’ve seen it go either way: you might think you can’t sustain the training you’ve been doing, so you cut your volume; or you think you need to crank volume through the roof to spur as much fat loss as possible. These tactics are not only unnecessary, they might undercut your progress.

Slashing volume at the start will decrease the energy you spend on exercise, meaning that the deficit you just implemented is smaller, or might not be a deficit at all. And spiking volume is just as needless: your nutrition, and not your exercise, should be what drives progress. What’s more, a big increase in volume, especially when you’re in a deficit, could lead to burnout, or worse—injury. Neither is a sustainable, achievable path to your goals!

You can make changes to your training volume (just like intensity or frequency) later. But, at the start, keep it the same.


The Ups & Downs of Training on a Deficit

One big difference with training on a deficit is how you’ll feel. It won’t always be bad, but it won’t be as good as when you’re on maintenance or in a nice surplus. Things will be more variable, and that’s okay.

You can deal with this by keeping a flexible training schedule. What I don’t mean by that is “training when you feel like it.” No, no. You need to be consistent and hit every muscle group frequently to help maintain muscle. I mean you can stay flexible with how you approach your training by “undulating” your workouts.

For each training day you schedule, give yourself one or two options for how intense and what type of workout you’re going to do. For instance, each workout could have a “hard” option with lots of high-intensity exercises and lots of reps, and a “moderate” option with fewer reps and all on machines. That way, if it’s leg day and you feel tired and hungry, you can get in the gym, put in some quality work, and not live in stressful fear of the brutal workout ahead of you. What’s more, you could recover better and make it to your next leg day in a few days.

Just like tracking macros, the biggest benefit to staying flexible is staying consistent.


Exercising Efficiently

As you get deeper into your deficit and the pounds are falling off left and right, you’ll probably start losing some energy in the gym. Maybe you move from one exercise to the next more slowly, and your rest periods get longer. Maybe you just can’t squeeze in as many exercises as you used to. It’s not the end of the world. But it does mean you have to be smart to stay ahead of it, which means staying efficient.

Efficiency in the gym is all about choosing the exercises that give you the most bang for your buck. If one movement can do the work of two or three others, you’re saving time and energy in the gym. That’s a huge win when you’re losing fat.

That’s why it’s important to focus your workouts around compound exercises. A compound movement is anything that involves multiple joints in each rep. This includes squats, deadlifts, bench press, rows, pull-ups, lunges… the list is almost endless. Because these exercises train more than one major muscle group at once (like how the squat trains the quads and glutes, or the bench press trains the chest, shoulders, and triceps) and you can train them heavier, they’re excellent choices for maintaining muscle on a deficit.

Cardio, or No?

Exercise can be useful to spur on fat loss, but (as we’ve covered) it shouldn’t be the primary driver. Still, cardio has its place in any diet and might be a very useful tool down the fat loss road.

But the key here is “down the road.” Just like making big changes to your in-the-gym training, adding a bunch of cardio right at the start of a deficit isn’t a good idea. While it could mean you get to eat more food in the beginning (because you’re burning more energy from exercise), it also means you’re taking away a plateau-busting wild card. That’s where cardio shines: When you’ve been dieting for a few weeks or months, your progress is beginning to slow, but you don’t want to keep eating less and less. Here, injecting some cardio can stimulate progress without having to starve. But, if you’ve already maxed-out your cardio credit, you’ve got nowhere to go but down. That’s why you don’t want to jump right into hours of cardio per week.

Instead, try ramping it up slowly throughout your diet. Or better yet, wait for those choice moments when progress stalls. Then, cardio can be a saving grace and not a chore.


Sticking to the Plan

Training while losing fat isn’t that different from training the rest of the time, which makes sense. If you were changing your activity as much as you change your nutrition, you’d have to change your nutrition even more. Plus, trying new things is great, but throwing yourself curve-balls when you’re hangry isn’t as fun as it sounds.

Ultimately, fat loss is simple: keep eating less (and maybe moving a bit more) until you win. The problem isn’t the physics, it’s the adherence. That’s why the best training program you can do while losing fat is the program you can stick to. Asking yourself, “Can I do this every week?” answers all the questions you need to know about training to lose fat and keep muscle. Trust your nutrition plan, lift weights, stay flexible, and lean on cardio only if you need it. Rinse and repeat until you win.