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How Many Calories does Muscle Actually Burn ?

The metabolic effect of adding muscle is misunderstood and greatly overstated. Most fitness professionals will tell you that each pound of muscle burns an extra 40-50 calories per day, which is just not true. The real number is about 6 calories. So you put on 10 pounds of muscle, and you’re buring an extra 60 calories a day…who cares? Thats a couple bites of a meal.

Fat cells are misunderstood as well, most people think of them as inert, but they actually burn about 2 calories per pound/per day by producing adipokines and various other tasks. So muscle is only 3x more metabolically active than fat. Not a huge difference. And if you lose 10lbs of fat, and replace it with 10lbs of muscle, that increase of 60 calories now drops to 40 extra calories burned per day due to the metabolic decline from the loss of fat cells.

That doesn’t mean that adding muscle won’t help you get lean faster, it just does so through a different mechanism than calorie burning, which is improved nutrient partitioning. So when you eat, you’re basically giving your food mapquest directions to your lean tissue, and away from fat tissue. As I’m sure many of you know, this is actually one of the ways steroids work their magic. There are numerous other ways adding muscle helps speed up fat loss, but I don’t want to write a book here.

A new study looked at the previous data on the subject with new testing methods. This research published in The American Journal of Clinical Nutrition affirmed the previous data regarding calories burned by various tissues and organs, summarized below, listed in calories burned per pound/per day (the study used kilograms, I’ve converted to pounds). The thing is, this isn’t new information, it just confirmed something we’ve known for a long time. The real question is, when will fitness professionals, media, and the general public finally accept it? The new data exposed by this study shows that the calories burned are over-estimated in people over the age of 50. Although statistically significant, the numbers aren’t really worth noting as the differences are very small.

Liver 90
Brain 110
Heart 200
Kidneys 200
Skeletal Muscle 6
Adipose Tissue (Fat) 2
Everything else (spleen, bone, adrenals, etc) 5

Here’s the new study:

Am J Clin Nutr. 2010 Oct 20.

Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure.

Wang Z, Ying Z, Bosy-Westphal A, Zhang J, Schautz B, Later W, Heymsfield SB, Müller MJ.

BACKGROUND: The specific resting metabolic rates (K(i); in kcal · kg(-1) · d(-1)) of major organs and tissues in adults were suggested by Elia (in . New York, NY: Raven Press, 1992) to be as follows: 200 for liver, 240 for brain, 440 for heart and kidneys, 13 for skeletal muscle, 4.5 for adipose tissue, and 12 for residual organs and tissues. However, Elia’s K(i) values have never been fully evaluated.

OBJECTIVES: The objectives of the present study were to evaluate the applicability of Elia’s K(i) values across adulthood and to explore the potential influence of age on the K(i) values.

DESIGN: A new approach was developed to evaluate the K(i) values of major organs and tissues on the basis of a mechanistic model: REE = ?(K(i) × T(i)), where REE is whole-body resting energy expenditure measured by indirect calorimetry, and T(i) is the mass of individual organs and tissues measured by magnetic resonance imaging. With measured REE and T(i), marginal 95% CIs for K(i) values were calculated by stepwise univariate regression analysis. An existing database of nonobese, healthy adults [n = 131; body mass index (BMI; in kg/m(2)) 50 y (n = 37).

RESULTS: Elia’s K(i) values were within the range of 95% CIs in the young and middle-age groups. However, Elia’s K(i) values were outside the right boundaries of 95% CIs in the >50-y group, which indicated that Elia’s study overestimated K(i) values by 3% in this group. Age-adjusted K(i) values for adults aged >50 y were 194 for liver, 233 for brain, 426 for heart and kidneys, 12.6 for skeletal muscle, 4.4 for adipose tissue, and 11.6 for residuals.

CONCLUSION: The general applicability of Elia’s K(i) values was validated across adulthood, although age adjustment is appropriate for specific applications.

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