Does a Calorie Surplus Help With Cardio?

You need an abundance of energy to build muscle. You use that energy to convert protein into muscle mass. You can get that energy by eating more food or by burning body fat (if you have an abundance of body fat).

It’s less clear whether you need extra calories to make cardiorespiratory adaptations. Will eating in a calorie surplus help you construct more blood vessels, gain new mitochondria, carry more oxygen in your blood, and build a bigger left ventricular wall in your heart?

Let’s dive into it.

Do Cardiovascular Adaptations Require a Calorie Surplus?

When you lift weights, you stimulate muscle growth, but your body will only build bigger muscles if you eat enough energy (calories) and building materials (protein). That means if you don’t eat enough, you won’t fully adapt to the stimulus of lifting weights. More on that in this article.

When you do cardio, you stimulate cardiorespiratory adaptations. It could be that a calorie surplus gives you more energy to invest in building blood vessels and a bigger heart, but there are also several reasons to suspect that it might not be as much of a limiting factor:

• Building bigger muscles is an ongoing investment. Muscles don’t just take energy to build; they also take energy to maintain and use. A pound of muscle burns around 6 extra calories per day. That means if you gain 20 pounds of muscle, you’ll burn around 120 more calories every day. If calories are already in short supply, it’s a bad investment. Muscles are for the calorically wealthy.
• Building a bigger cardiovascular system isn’t much of an ongoing investment. A stronger heart pumps blood more efficiently, slowing your resting heart rate and thus slowing metabolism (study). Blood vessels don’t require much upkeep, either. And none of these adaptations are heavy, meaning they don’t cost energy to lug around.
• Hearts are relatively small. The left ventricular wall of an athlete’s heart is around 48% bigger than the average person’s, making it about 0.1 pounds heavier (study). It doesn’t take many calories to build or maintain an extra 0.1 pounds of muscle mass.
• Most cardio studies don’t even bother putting the participants on a bulking diet. The participants still see great gains in fitness.

Is There Any Research On Calories & Cardio?

I couldn’t find any studies where researchers put people on a cardio routine, manipulated their calorie intake, and measured how it affected their results. I also couldn’t find any experts talking about it. So I asked one.

I reached out to Dr. Eric Trexler, an exercise scientist with a Ph.D. in nutrition. He reviews strength and hypertrophy research for Monthly Applications in Strength Sport (MASS). Most recently, he reviewed a study covering how our hearts adapt to cardiovascular exercise and resistance training. I asked him if calorie intake affects cardiovascular adaptations. He told me:

• Heart vascularization and maintenance of myocardial contractility are pretty high on the biological priority list, so I suspect those processes are pretty robust against modest changes in energy availability. I doubt that a calorie surplus would meaningfully move the needle.
• I doubt that an advisable (i.e. not egregiously extreme) calorie deficit would hinder cardiac adaptations, but that’s just a hunch. I’m not aware of research on the topic. It could be out there, but I haven’t seen it.

Summary

It’s hard to say for sure how calorie intake affects cardiovascular adaptations. As far as I know, there aren’t any studies specifically looking into it. It’s unlikely you need much of a calorie surplus to maximize your results. It’s unclear if you can make ideal cardio adaptations while eating in a calorie deficit.

Many studies show great (but perhaps not ideal) cardiovascular adaptations when people are slowly losing weight. As long as you’re bulking or cutting at a healthy pace, you probably don’t need to worry about how it will affect your cardiovascular adaptations.

Alright, that’s it for now. If you want more muscle-building information, we have a free muscle-building newsletter. If you want a full exercise, diet, and lifestyle program to help you build muscle and improve your cardiovascular health, check out our Bony to Beastly (men’s) program or our Bony to Bombshell (women’s) program. Or, if you’re already an intermediate lifter, check out our customizable Outlift Intermediate Hypertrophy Program.

Shane Duquette

Shane Duquette is the co-founder and creative lead of Outlift, Bony to Beastly, and Bony to Bombshell, and has a degree in design from York University in Toronto, Canada. He's personally gained 65 pounds at 11% body fat and has ten years of experience helping over 10,000 skinny people bulk up.

Marco Walker-Ng, BHSc, PTS

Marco Walker-Ng is the co-founder and strength coach of Outlift, Bony to Beastly, and Bony to Bombshell, and is a certified trainer (PTS) with a Bachelor's degree in Health Sciences (BHSc) from the University of Ottawa. His specialty is helping people build muscle to improve their strength and general health, with clients including college, professional, and Olympic athletes.