We need an abundance of calories to build muscle. We use it to convert protein into muscle mass. Without it, we won’t build muscle. To get those extra calories, we can burn excess body fat or eat more food.
It’s less clear whether we need extra calories to make cardiovascular adaptations. Will eating in a calorie surplus help us build more blood vessels? Will a calorie deficit interfere with our ability to build a stronger heart?
Do Cardiovascular Adaptations Require a Calorie Surplus?
When we lift weights, we stimulate muscle growth, but our bodies will only build bigger muscles if we’re eating enough energy (calories) and building materials (protein). That means if we aren’t eating enough, we won’t fully adapt to lifting weights.
When we do cardio, we stimulate cardiovascular adaptations. “Cardio” refers to our hearts, which will grow bigger and stronger. “Vascular” refers to our blood vessels, which will grow more numerous. It could be that a calorie surplus gives us more energy to invest in building blood vessels and a bigger heart, but there are also several reasons to suspect that our calorie intake wouldn’t affect cardiovascular adaptations:
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 six extra calories per day. If you gain twenty pounds of muscle, you’ll burn around 120 more calories every day. That isn’t a ton of extra calories, but if calories are already in short supply, it’s a bad investment. Muscles are for calorically wealthy people.
Building a bigger cardiovascular system isn’t much of an ongoing investment. A stronger heart pumps blood more efficiently (study), making it relatively easy to fuel, even when calories are in short supply. The same is true with our blood vessels. They’re relatively easy to maintain. We could imagine, then, that our bodies can sustain cardiovascular adaptations without needing a bunch of extra calories.
Our 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 67 grams heavier (study). That’s only 0.1 pounds heavier. Gaining 0.1 pounds of muscle in your heart isn’t in the same order of magnitude as gaining 20 pounds of skeletal muscle from lifting weights.
Most studies find great cardiovascular adaptations without putting the participants on a bulking diet.
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:
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.
I doubt that a calorie surplus would meaningfully move the needle.
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.
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. However, we do know that people get great cardiovascular adaptations whether they’re slowly losing weight, maintaining their weight, or slowly gaining 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.
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 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.
