The Myth about Muscle and Your Metabolic Rate

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."

The idea is that for every pound of new muscle, your body will burn an extra 60 calories per day. Add five pounds of new muscle and you will automatically burn an additional 31 pounds of fat in a year... or so the theory goes, anyway.

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.

So, where did 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.

Let me give you a couple of examples...

The first comes from an 18-week study of 26 sedentary men published in the Journal of Applied Physiology [3]. 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.

In another trial, women who trained with weights three days a week for six months gained 2.9 pounds of fat-free mass [1]. In that time, their resting metabolic rate increased by an average of 60 calories per day.

Dividing the increase in resting metabolic rate (60 calories) by the increase in fat-free mass (2.9 pounds) gives us a figure of 20.7 calories per pound.

However, even this figure overestimates the metabolic rate of muscle.

Methods for measuring resting metabolic rate and body composition vary widely in their precision and accuracy. We don't know for sure if the change in resting metabolism was because of the extra muscle, or whether it was due to measurement error. The control group in this study did no exercise, yet their resting metabolic rate increased by 31 calories per day.

In addition, other studies show an increase in resting metabolic rate even when gains in fat-free mass are taken into account [2]. 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 [4]. According to some estimates, fat has a daily metabolic rate of two calories per pound per day, with muscle clocking in at just six calories per pound [5].

In other words, losing two pounds of fat and replacing it with two pounds of muscle will increase your resting metabolic rate by less than 10 calories per day.

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 for one 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.

Wolfe does mention that this number assumes "a constant rate of protein turnover." Most types of resistance exercise will increase 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.

It's also worth mentioning that 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.

What does all of this mean for you?

Despite the fact that the resting metabolic rate of muscle is not as high as previously doesn't mean that training with weights is pointless if you want to lose fat. Far from it. In fact, resistance exercise will improve your body composition in a number of different ways.

Firstly, with a properly designed weight-training program (see How to Fight Fat and Win II in the Members-Only Area), you'll burn more calories and more fat in the hours after exercise, although it's my opinion that the light-weight, high-repetition "toning" workouts most people do have only a minor impact on post-exercise metabolism.

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 rather than 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.

About The Author Christian Finn holds a masters degree in exercise science, is a certified personal trainer and a regular contributor to Men's Health, Men's Fitness and other popular fitness magazines. If you're stuck in a rut with your current exercise and diet plan... fed up with only losing a pound here and there... or still skinny after months (or even years) of trying to build muscle and gain weight... Christian can help you achieve your goals once and for all. Click here now to find out how Christian can help you

Related Articles

• Belly Fat and How to Beat It
• How to Fight Fat and Win II (Members Only)
• The Maximum Muscle Plan (Members Only)
• How To Burn More Fat In Less Time

References
1. Poehlman, E.T., Denino, W.F., Beckett, T., Kinaman, K.A., Dionne, I.J., Dvorak, R., & Ades, P.A. (2002). Effects of endurance and resistance training on total daily energy expenditure in young women: a controlled randomized trial. Journal of Clinical Endocrinology and Metabolism, 87, 1004-1009
2. Pratley, R., Nicklas, B., Rubin, M., Miller, J., Smith, A., Smith, M., Hurley, B., & Goldberg, A. (1994). Strength training increases resting metabolic rate and norepinephrine levels in healthy 50- to 65-yr-old men. Journal of Applied Physiology, 76, 133-137
3. Van Etten, L.M., Westerterp, K.R., Verstappen, F.T., Boon, B.J., & Saris, W.H. (1997). Effect of an 18-wk weight-training program on energy expenditure and physical activity. Journal of Applied Physiology, 82, 298-304
4. Wajchenberg, B.L. (2000). Subcutaneous and visceral adipose tissue: their relation to the metabolic syndrome. Endocrine Reviews, 21, 697-738
5. Wang, Z., Heshka, S., Zhang, K., Boozer, C.N., & Heymsfield, S.B. (2001). Resting energy expenditure: systematic organization and critique of prediction methods. Obesity Research, 9, 331-336