What to eat if cardio’s hurting your muscle gains

Published on 18 October 2021

If you love the rush of smashing out some cardio but finding you’re not only losing weight but also muscle mass, get ready to get back on the gains train. We asked Aquanation and Aquahub nutritionist and personal trainer Byron Manning for his tips for getting the best of both worlds. 

Does cardio burn muscle?

Yes and no. According to Manning, it’s not that you’ll burn muscle during that particular cardio session but rather throughout the day.

“When you’re doing cardio, you are straining a lot of different muscle groups pretty repetitively for a decent amount of time, in that process you’re pulling on all sorts of fuel source,” says the personal trainer.

When it comes to what’s fuelling your workout, he says your body “might start with your fat stores, then it’ll move towards your carbohydrates, which then break down into smaller sugars, which in turn converts into glucose. Any stored glucose will be converted into glycogen and stored in the muscles which your body uses to fuel your workout as the intensity increases”.

He adds that in the background of your cardio workout is a very small contribution to amino acids (which are pretty much your protein).

Can cardio burn muscle?

The short answer is, yes, but only if you’re not doing enough weight training or supplementing your workouts with a nutritious diet. Manning clarifies it’s all about what your cardio session does to your overall daily energy expenditure.

“People who are doing cardio typically have pretty big (caloric) expenditures and that makes it hard for them to eat up to that amount, and over a period of time that’s where you’ll see losses of cardio weight, which will usually be some proportion of muscle.”

Filling up the tank

What you put into your body impacts your output no matter what type of training you fancy.

According to Manning, one common factor when incorporating cardio into a workout regime is not eating enough.

“One of the biggest contributors is not eating as much as you need and over a long period of time this will be what results in you losing muscle mass,” he explains.

So essentially, you can’t build muscle if you’re not eating more calories than you’re burning during a cardio workout, otherwise known as a calorie deficit.

And while protein brings all the gym junkies to the yard, it’s also super important for cardio fanatics too. A 2016 study published in The American Journal of Clinical Nutrition showed that consuming protein higher than the recommended dietary allowance during an ‘energy deficit’ can help to preserve lean body mass (LBM), particularly when combined with exercise.

Switch up your workouts

It’s the common debate when it comes to fitness: cardio or strength training? Which workout is best, and which can you cut from your exercise routine? The reality is cardio (aerobic) and resistance training (anaerobic) don’t need to be mutually exclusive – nor should they be.

Short answer is both cardio and strength training need to be included in a well-rounded exercise program, advises Manning.

“If you’re fanatical about your cardio and not doing any resistance training you’re not really giving that muscle a reason to hang around,” he says.

And while that the slower pace of strength training might not be every cardio enthusiast’s cup of tea, there are ways to make it your jam.

“One way to motivate cardio fans is that resistance training reduces their risk of injury in the long run. That means your cardio career is going to last longer if you’ve got some resistance training in your program as it impacts your recovery and overall muscle growth,” adds Manning.