What is the real resting metabolic rate of muscle?

The Myth about Muscle and Metabolism

One of the big myths about muscle and metabolism is the idea that for every pound of new muscle, your body will burn an extra 50-100 calories per day.

According to Adam Zickerman, author of Power of 10: The Once-a-Week Slow Motion Fitness Revolution, “three extra pounds of lean muscle burns about 10,000 extra calories a month.”

Zickerman also says that three extra pounds of muscle “burns as many calories as running 25 miles a week, or doing 25 aerobic workouts a month without leaving your couch.”
You’ve probably read similar claims that muscle “burns calories around the clock just to maintain itself, even while you are sleeping or sitting at a desk.”

When you gain muscle, your resting metabolic rate (the number of calories your body burns at rest) does go up. But this increase is a lot less than the 50-100 calorie figure you’ll often see written.

Where does the 50-100 calorie figure actually come from?
I have no idea. It just seems to be one of those myths that have been around for so long that its accuracy is no longer questioned, and probably exists for the same reason we have misconceptions about a lot of things. Somebody says something, somebody repeats it, and then we repeat it. Suddenly it’s established as fact.

In studies that have tracked changes in muscle mass and metabolism, it might appear that the metabolic rate of muscle is somewhere in the region of 50-100 calories per pound. But when you take a closer look, you’ll see that things are not quite so simple.

A good example comes from a study that tracked a group of 26 men during an 18-week program of resistance training. During the first eight weeks, the men gained roughly 2.8 pounds of fat-free mass. The average daily metabolic rate increased by 263 calories per day.

Dividing the increase in resting metabolic rate (263 calories) by the increase in fat-free mass (2.8 pounds) gives us a figure of 94 calories per pound. However, we can’t assume that this figure represents the metabolic rate of muscle.
Why not?

The first problem is the daily metabolic rate includes the energy cost of physical activity. We can’t say for sure that the increase in calorie expenditure was because of the extra muscle alone.

But that’s not the only problem.

From week 8 to week 18, the men gained another 1.8 pounds of fat-free mass. If muscle had such a big impact on metabolism, we’d expect to see another rise in the men’s metabolic rate. But this didn’t happen. Nor was there any change in sleeping metabolic rate during the study.

What’s more, methods for measuring resting metabolic rate and body composition vary widely in their precision and accuracy. We don’t know for sure if any change in resting metabolism is because of extra muscle, or whether it’s due to measurement error.

In addition, other studies show an increase in resting metabolic rate even when gains in fat-free mass are taken into account. Researchers think that mechanisms other than the increase in fat-free mass (such as changes in the activity of the sympathetic nervous system) are partly responsible.

And fat is not simply a “dead” tissue. It secretes proteins such as leptin and cytokines, which can affect your metabolism.

What is the real metabolic rate of muscle?

Muscle actually has a very low metabolic rate when it is at rest, which is most of the time.

And the metabolic rate of muscle pales in comparison to other parts of the body.
In fact, the heart and kidneys have the highest resting metabolic rate (200 calories per pound). The brain (109 calories per pound) and liver (91 calories per pound) also have high values. In contrast, the resting metabolic rate of skeletal muscle clocks in at just 6 calories per pound, with fat burning just 2 calories per pound.

Organ or tissue	Daily metabolic rate
Adipose (fat)	2 calories per pound
Muscle	6 calories per pound
Liver	91 calories per pound
Brain	109 calories per pound
Heart	200 calories per pound
Kidneys	200 calories per pound

In other words, while skeletal muscle and fat are the two largest components, their contribution to resting energy expenditure is smaller than that of organs. The vast majority of the resting energy expenditure of your body comes from organs such as liver, kidneys, heart, and brain, which account for only 5% to 6% of your weight.

As is often the case with these things, not everyone agrees on the exact figure.
Writing in the American Journal of Clinical Nutrition, Robert Wolfe, Ph.D., Chief of Metabolism and Professor of Biochemistry at the University of Texas Medical Branch, points out that, “every 10-kilogram difference in lean mass translates to a difference in energy expenditure of 100 calories per day, assuming a constant rate of protein turnover.”

That’s 10 calories per kilogram of muscle, or a little less than 5 calories per pound — not too far away from the previous estimate of 6 calories per pound.

Rest versus recovery

I do want to make an important distinction between resting muscle and recovering muscle. The estimates of the resting metabolic rate of muscle I’ve just given do make one assumption — a constant rate of protein turnover.

However, most types of resistance exercise will accelerate protein turnover (an increase in the rate of protein synthesis and breakdown), which is going to increase calorie expenditure in the hours (and, in some cases, days) after exercise.

And there are studies to show that the more muscle you have, the more calories you’ll burn after an intense workout.

When exercise ends, it takes time for everything to get back to normal. Depleted glucose and fat stores need to be refilled. Damaged muscle cells need to be repaired. All of this requires energy.

And the more rebuilding that has to be done, the more calories (mainly from fat) are being burned after your workout is over.

Or to put it another way, while the metabolic rate of resting muscle isn’t as high as previously thought, the metabolic rate of recovering muscle means that people with more muscle mass are going to burn more calories in the post-exercise period.

What all of this means for you
If you were to lose two pounds of fat and replace it with two pounds of muscle, your resting metabolic rate will increase by less than 10 calories per day.

It would take a vast amount of muscle to substantially increase your metabolic rate — far more than most people are going to build in the gym.

Which brings me to another important point.

Unless they’re very overfat, returning to exercise after a layoff, or just starting an exercise program, very few people gain a lot of muscle and lose a lot of fat at the same time. Your body just isn’t that great at doing both things at once.

That’s why I recommend you focus on one of two goals when you’re trying to get in shape — building muscle while minimizing fat gain, or, losing fat while preserving muscle.

Despite the fact that the resting metabolic rate of muscle is not as high as previously thought doesn’t mean that training with weights is pointless if you want to lose fat. Far from it. In fact, lifting weights will improve your body composition in a number of different ways.
Firstly, strength training burns calories (and fat). Not just during your workout, but – provided you train hard enough – after it’s finished as well.

Second, if you don’t do some kind of resistance exercise while you’re dieting, a lot of the weight you lose will come from muscle as well as fat.

If you are fortunate enough to gain a significant amount of muscle while you’re losing fat, the impact of the extra muscle on your resting metabolic rate will be small, and certainly won’t amount to 10,000 extra calories a month.

by Christian Finn