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Why is muscle 600 calories per lb?18936

the_can_man_can private msg quote post Address this user
I am curious about the science behind this.

So a pound of human fat tissue is about 13% water and 87% lipid, which means 395 grams of stored fats. At 9 cals per gram, that's 3555 calories per lb of fat.

But now I don't understand where the 600 cal figure comes from for human muscle. Muscle is about 80% water, 20% protein. So about 91g protein per lb muscle tissue. At 4 cals per gram, that's 364 calories. A far cry from 600!

What did I miss?
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eknight private msg quote post Address this user



Not really that much different than the human body. -3X
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the_can_man_can private msg quote post Address this user
So in that beef, at any rate, it has protein = 22% by weight, fat = 6.5% by weight.

If I round those down to 20% and 6% then 454*(.2*4 + .06*9) = 608.36 calories, which is pretty close!

I didn't realize human muscle tissue had that much fat, though. Is that fat not oxidized as readily as, say, adipose tissue? Is it only burned if the lean tissue around it is also being catabolized?

And what about glycogen? Isn't that stored in the muscle somewhere, which would be formed from carbohydrates at 4 calories per gram? Does this not factor into the caloric content somehow?
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eknight private msg quote post Address this user
Of course human muscle tissue has that much fat. Step back and think about what you just wrote- 6% for the beef. You know how lean 6% body fat is for people??? That's not a lot of fat at all!

Re. glycogen, an average (175-180 pound) male might store 400g of glycogen in the muscles of his entire body. That's about 2000 kcals. Using our 180 pound male with his absurdly low 6% body fat that equates to: 180*.94= 169 pounds of lean body mass. That's obviously not all muscle. In fact it's only 68 pounds of muscle. Ok so 2000 kcals/68 pounds equals a whopping 29 kcals of stored glycogen. So there you have it- there's glycogen in muscle... except... except... except... when you die.

When you die, ATP attaches to your muscle fibers, undergoes hydrolysis and detaches (what we think of as the sliding filament theory of actin and myosin cross-bridge formation when we are alive) in a continuous process until all of the ATP in the cell is used up, causing the muscles to stay contracted, since the absence of ATP and ADP is a state in which myosin is bound tightly to the actin crossbridge (aka, rigor mortis). Google "biochemistry of rigor mortis," for a more detailed review. There are several out there. -3X
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the_can_man_can private msg quote post Address this user
How do you get 2000 kcals from 400g glycogen? Wouldn't it be closer to 1600 kcals? (4 kcals / g carb?)

With you on 169 lbs lean mass, but then how do you get to 68 lbs of muscle?

As for the whole 6% bodyfat thing, yeah certainly seems a lot more obvious now when you put it that way.

I had assumed that if someone was at (for example) 6-8% bodyfat, that it was still due to adipose tissue -- just not very much of it left (I also assume that it's not really possible to burn all your adipose tissue so the body holds onto it for dear life if you try to cut fat even further). Didn't figure there was extra fat in the muscle tissue.
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eknight private msg quote post Address this user
Sorry- late. Yes, 1600 kcals. Doesn't really matter though since it's all used up.

Re. the 169/68, you understand that out of 169 pounds most of it is bones, organs, fluids, etc. and that less than half is actual muscle right? The clinical figures I'm familiar with are 40% of LBM is actual muscle among men and 30% is muscle among females, disregarding outliers. -3X
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the_can_man_can private msg quote post Address this user
Wasn't familiar with the 40% / 30% figures but that's good to know / makes sense. I know most of lean mass is bone and organ and such but I didn't know what calculation you were doing exactly to get to that number, so thanks!

So really it's more like 1600 kcals/68 lbs = 23 calories of glycogen per lb of muscle tissue, which is about 6 grams, or 1.3% by weight. Not very much at all -- surprising!
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the_can_man_can private msg quote post Address this user
So I guess that 600 calorie figure does make sense.

Apparently if your body catabolizes the muscle, it only gets 600 calories out of it, whereas building that muscle (for some reason) requires like 2600 calories in surplus (I don't know where these excess calories go, though -- perhaps fat).

Although this would suggest a muscle/fat gain ratio of 600/2600 = 20%/80%.
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eknight private msg quote post Address this user
Here's a link to an MRI study that came up with similar figures to the 40/30: http://m.jap.physiology.org/content/89/1/81

Not sure why it's surprising that we don't store that much glycogen. It's not necessary to. We eat. We have fat. We are by and large, lazy compared to our ancestors. And several of us have a pancreas that is there for the sole purpose of making sure we DON'T store excessive glucose in our bodies!

You also understand that building muscle tissue is an active process that requires energy right? -3X
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the_can_man_can private msg quote post Address this user
Well, surprising to me because I was under the assumption that our body is consuming glucose left and right (esp. the brain) for fuel, so I thought glycogen stores needed to be quite plentiful. But I guess the "quick-energy" from glycogen is sufficient as a first-order energy-draw when there is plenty of stored triglyceride in the adipose tissue to tap into for backup.
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eknight private msg quote post Address this user
Your brain runs on about 130 grams of glucose in a day. -3X
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the_can_man_can private msg quote post Address this user
"You also understand that building muscle tissue is an active process that requires energy right?"

I don't know the underlying mechanics, no. If I eat a theoretical surplus of 2600 calories (under the assumption it's all going to muscle-building), and the muscle itself only has 600 calories available for catabolysis, I don't know where the extra 2000 goes. I don't imagine it just disappears into heat because that would imply that if you eat a large surplus to build muscle, you wouldn't get that much heavier.
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eknight private msg quote post Address this user
That's an incorrect assumption though. Just because you eat XXX kcals doesn't mean they're all going to do one thing or another. I feel like this is a little over your head at this point. Based on your first post I thought you had a better grasp of the basics. I'd encourage you to read up on some A&P and nutrition to help yourself out there. -3X
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the_can_man_can private msg quote post Address this user
I need to clarify: I know they don't all go to one thing or another (which is why I said under the assumption -- as in a theoretical / hypothetical example). I understand that, for example, on a cut, muscle retention is maximized by a high protein intake and heavy weight training, and similarly it's how you build muscle on a bulk. But the calories you spend under your TDEE / over your TDEE usually get split up into various pieces (which is why if you eat at a 500 calorie deficit for example, you don't lose exactly 1 lb of fat a week since it's not 100% fat loss).

However the fat and muscle deltas are not the same in deficit vs. in surplus, which is one reason why I wanted to learn more about what's going on physiologically / mathematically.
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the_can_man_can private msg quote post Address this user
"I feel like this is a little over your head at this point. Based on your first post I thought you had a better grasp of the basics."

Come on, man, that's not cool.

I most certainly do understand the basics, and this stuff is not over my head.
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Yeags private msg quote post Address this user
To much thinking
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