Here’s a great comment by ‘Gokul’ to explore some of the facts behind muscle and metabolism. My comments in RED
I think you are wrong Brad.
Take 2 hypothetical males of the same height and frame size. 1st guy(thin) weighs 60kgs (132 pounds) and has 6% body fat.
2nd guy(muscular) weighs 80 kgs (176 pounds) and has 6% body fat.
Now according to Katch mc ardle’s formula: (RMR = [LBM (KG) x 21.6) + 370])
1st guy BMR is 1588 cal.
2nd guy BMR is 1994 cal.
Lean mass of 1st guy from Katch’s formual 56.4 kgs. (124 pounds)
Lean mass of 2nd guy from Katch’s formula is 75.2 kgs. (165 pounds)
(That’s a 41 pound difference, very difficult for two guys of the same height to have a 41 pounds difference in skeletal muscle mass and both be very lean.. but I’ll let it slide)
Now assuming that both have similar size internal organs which is a safe assumption i presume, the difference in lean body mass in this case refers to muscle which is 75.2 – 56.4 = 18.8 kgs. (ONLY if they are the same height, which then makes the 40 pounds Lean Mass difference highly suspect)
Now difference in BMR of the 2 guys is 1994 – 1588 = 406 cals. (correct)
So calories needed to maintain 1 kg muscle mass = 406/18.8 = 21.6 calories per Kilogram or 10 Calories per pounds. (correct)
Now the point here is that the 80kgs guy requires 400 calories more than the 60kgs to maintain his weight including his lean mass. So if both are trying to maintain their weight, the 80 kgs guy can eat 400 calories more than the 60 kgs guy without getting fatter which means he burns 400 calories more than the smaller guy effectively. (makes sense based on your assumptions)
So the conclusion is that muscular guys can eat more than skinny guys because their extra muscle will burn extra calories. (explanation below)
The mistakes made here is are very common ones. They’re made by trainers, students, heck even some PhD’s.
The first mistake is trying to use McCardle Katch (or any equation for that matter) to compare differences between two people. That’s not what these equations were meant for. Nor were they made for estimating the metabolic changes that result from adding or subtracting skeletal muscle.
This is because these equations utilize a homogenous ‘21.6’ as the metabolic rate for ALL lean body mass combined. (Hence why our commenter above came to the conclusion that 2.2 pounds of muscle (a Kilogram) burns 21.6 calories per day).
The truth is we know the metabolic rates of all of the compartments that make up ‘lean body mass’ this includes the highly active heart, liver and kidneys and the (by comparison) barely active component of skeletal muscle (when at rest).
So the 21.6 is the approximate value of all of your lean body mass combined, but NOT the ‘calorie’ burn of each individual compartment of your lean body mass. (Muscle burns about 6 calories per pound, per day when at rest).
So our two men above would still have a very significant 250 calorie difference in daily Resting Metabolic Rate.
The question is, can two men of equal height vary by 40 pounds of skeletal muscle? And if they could, would either man be considered healthy?
Chance are, these two men would be different heights, and as we know, metabolic rate is scalable to height, since our highly metabolic organs are also scalable to height. – This is a main reason why a 6’2″ man has a higher metabolic rate then a 5’6″ women…I know, I know – not fair 😉
Bottom line – you can’t really use metabolic equations to try and identify metabolic changes that result from increases or decreases in Lean body mass. It’s an easy mistake to make, and one that’s not properly explained on most websites that provide these calculators.
BP
