How Many Calories Does it Take to Catabolize a Lb of Lean Mass?

(Windmill Tilter) #1

When we lose 4lb of fat, in most cases, we also lose somewhere around 1lb of lean mass. There are arguments to made that lean mass can be conserved with adequate protein and resistance training, but that’s not what my question is about. Lets just assume that 1lb of lean mass has been catabolized.

What I’m wondering is how metabolically expensive it is to break down our own lean mass. I’ve read that the metabolic cost of breaking down protein that we ingest from animal sources as somewhere in the neighborhood of 25% of calories e.g. if you eat 1000kcal of steak, you use up 250cal just digesting it. Well this is a bit different because your digestive system isn’t even involved, autophagy does all the work.

Does anybody know how many calories it takes to catabolize lean mass? I’ve never seen anything about this, but surely someone has researched it!

(Robert C) #2

I am definitely not an expert here but I do not think metabolism and catabolism are similar.

Metabolism seems to be a process which has different costs for different inputs.

Catabolism seems to simply be destruction (I think) so I am not sure there is any cost to it (i.e. muscles are simply put into a situation where they are falling apart / disintegrating).

Maybe some expert can jump in here but I haven’t heard of any caloric cost for the body going after stored glycogen, fat or muscle. I feel like if there was, someone would be trying to sell a pill to exaggerate the effect and claim a fat burning benefit.

(Windmill Tilter) #3

Definitely not very similar. They both have an energy cost though. I’m trying to understand the energy cost of the latter.

Everything that happens within the body has an energy cost. If thinking has an energy cost, breaking down a muscle cell into it’s constiuent amino acids definitely has an energy cost!

Breaking down a fat cell might take only 1 kcal, and yield 90. Breaking down a muscle cell might take 10kcal and yield 40 or something like that. I don’t have a clue what the real numbers are, I’m just trying to get a rough estimate.

(You've tried everything else; why not try bacon?) #4

As I understand it, that 25% cost is the “thermic effect” of metabolizing amino acids through the Krebs cycle, and not precisely what you are asking here. In autophagy, proteins are broken down into their constituent amino acids, which enter the labile pool for reuse. You could do a search on “proteolysis” or “protease” and see if anyone has calculated the cost of the reaction—it’s very likely been done, and Google Scholar should be able to turn it up.

I do know that enzyme reactions are generally less costly, because of how the enzyme potentiates the reaction, but you’d have to figure in whether any of the enzyme gets consumed in the reaction, or whether it simply acts as a catalyst, etc. As I understand it, the real metabolic cost of metabolizing protein comes from the work required to deaminate the amino acids and convert the freed nitrogen into uric acid (a process with several steps), and then the deaminated acids yield a lesser amount of ATP for the amount of energy it takes to run them through the Krebs cycle.

Your analysis of the thermic effect of autophagy would have to include, therefore, an estimate of how much of the freed amino acids would likely be handled this way, and I have no idea how you could figure that. It might be valid simply to calculate through the proteolysis step and ignore what happens to the amino acids thereafter. If @richard has covered any of this in hs course work, he might be persuaded to work up something.

(You've tried everything else; why not try bacon?) #5

Metabolism is generally defined as the sum of anabolism and catabolism, the former of which is the process of building new tissue, and the latter the process of breaking tissue down—generally speaking, of course. Bikman speaks of the “metabolic milieu,” because there is generally a predominant “tone” to what the body is doing, even though there are certain anabolic processes that operate during catabolism, and vice versa.

As Bikman presents it, the key to whether the body is in primarily an anabolic or a catabolic state is the ratio of insulin to glucagon: a high ratio indicates anabolism is predominating, a low one that catabolism is predominating.

To give you a couple of examples, the formation of new muscle is an anabolic activity, because it involves assembling amino acids into proteins, and proteins (plus some fats for the cell walls) into tissues. This happens in the presence of insulin, IGF-1, and HGH.

Ketogenesis and fatty acid metabolism are catabolic, because they start with fatty acids and break them down into ketone bodies, which can then be further broken down into water and carbon dioxide during the course of producing adenosine triphosphate (ATP) for the body to use as energy. These are processes stimulated by glucagon, when they happen in the liver.

(Robert C) #6

As previously stated, I have no idea but, what might be more important than knowing the net yield is how to manipulate it.

In metabolism, the net yield can be manipulated by changing the macros - each having a different “thermic effect”.

But, you are asking just about lean mass - so no manipulation through macro change as it is just one macro. To manipulate the cost to catabolize it seems like the only way is to try to avoid it.

For example - let’s say you want to fast 50% of a week for 10 weeks - you could fast Monday dinner to Friday breakfast (84 hours) or you could do alternate day fasting (i.e. no food every other day).

Again, I do not know but, from what I understand, you would catabolize more lean mass on alternate day fasting because you are in the fasting startup mode 3 or 4 times a week. Instead, fasting Monday dinner to Friday breakfast, fasting startup mode happens once and the protective effects of the significantly raised HGH avoid having you catabolize lean mass for the remainder of the fast (or just greatly lower it).

When I write “fasting startup mode” I mean the time in the first 24 hours when the body is realizing it isn’t getting any calorie intake and starts hunting for local stores of energy (glycogen, protein and fat). I assume being fat-adapted means this time will be more muscle sparing as fat is easier to use.

Not sure if this is all correct - not an expert or anything.