Hmmm - what an interesting question!
Not sure if I can answer it but I've given it some thought ....
So lets say both men, stripped down to skeleton and organs weigh 10st.
So one is carrying, say, 2st of muscle and 5st of fat.
The other is carrying 2st of fat and 5st of muscle.
Muscle is the body's 'furnace' - Calories are the fuel. So I would imagine the muscley guy would be the more efficient fat burner. He could probably eat more calories than the fat guy before gaining any weight providing he was using those muscles. (what a thought!!
)
The fat guy would still use more cals than a normal weight guy because it takes more energy to propel his bigger weight around. That's why our calorie requirement comes down when we lose weight: not because our metabolism has slowed down as a direct result of dieting. That's also why bigger overweight people lose weight faster in the beginning - the calorie deficit is greater.
Don't think I've really answered the question there but it's something to think about ...
