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How Exactly Does Catabolism Affect your Body?


I'm not sure I understand what catabolism does to your body and muscle mass, or even entirely what it is - it has something to do with muscle loss, right? I haven't had much appetite recently and I've been eating less, is this going to lead to muscle loss?

I'm still improving on most of my lifts in the gym but my calorie intake has been somewhere in the 2000s rather than the 3000 or so I need to gain, my weight has dropped somewhat as well but I can't tell if it's muscle or fat that's gone. Could someone explain this to me? Thank you.


catabolism is basically your body eating its own muscle because it needs energy, or just doesn't need the muscle.


Catabolism means to break down large complex molecules into smaller and simpler ones. When your body needs energy and is in a hypocaloric state, it will break down proteins and fats (and carbs if you're consuming them).

However, muscle catabolism is not immediate. If you're eating enough protein, I'm sure you won't lose muscle, especially if you're lifting heavy enough. And since you stated yourself that your lifts are improving, I'm pretty sure the weight that you've dropped is mostly (if not all) fat.



anabolic = muscle growing

catabolic = muscle wasting


I think that is too simplistic of an explanation. A better question:

Does lipolysis only occur in a state of catabolism, or can it also occur during anabolism?

What about glycolysis?


Yes Beast's explanation is oversimplified.

pzeh posted a good response to the op's question.

Anabolism is any bodily process that requires making larger structures from smaller ones and catabolism is any process that requires breaking down larger structures into smaller ones.

Both processes take place throughout the day even in a caloric surplus. If no catabolism ever occurred then you would not have any energy to run your body.

OP, you won't lose muscle if your lifts are staying the same.

If your appetite is decreasing significantly then there's probably a psychological reason why you can't eat as much.


Exactly. To say that anabolism = muscle building and catabolism is muscle wasting is wrong. Both processes take place on a continuous basis. i

If NET anabolism takes place over time (such as a week) then more tissue is gained (this can be both both muscle and fat)

Conversely, if NET catabolism takes place over time then more tissue is lost compared to gained (and if strength levels stay the same / improve, you can be assured that mostly fat was lost)

as far as your diminished appetite goes, once someone strays too far from their genetic "set point" of weight / bodyfat, the body begins to fight back to maintain its preferred state. Obviously you have reached that point as your body is telling you it doesn't want to get much bigger. This is when you must begin to "force feed" yourself if you wish to get bigger. More calorie dense food (like dried fruit, whole milk, bagels w/ peanut butter etc.) will help.


Whoop, biochemistry is my specialty, I'll be graduating in 2010 so I hope I can clear something up.

Everybody is correct, an anabolic pathway is strictly "building something" to release energy, and a catabolic pathway is "breaking things down" to release energy.

Specifically in our (T-Men) interests is regarding muscle tissue/fat cells.

Glycolysis occurs 24/7 in humans unless you're trying to enter a ketogenic state... it's just the simplest form of carbohydrate catabolism, and it sucks at that since it's the most ancient energy pathway we have and mitochondria have 100x faster rates of creating ATP.

The catabolism of muscles and fat that we are talking about is actually glucose anabolism... if that makes sense. It's what happens when your body is lacking in glucose.

Specifically it's called "gluco-neogenesis", which basically means "creating glucose". The human body can create glucose from any citric acid cycle intermediates (any amino acid), and odd number fatty acid chains. It cannot use lysine and leucine (BCAAs anybody?).

So basically, when you're out for a run.. your body runs out of carbs. It starts to break down triglycerides to get some gluconeogenesis started. AT THE SAME TIME, it will use amino acids to create even more glucose because the two pathways are not mutually exclusive.

I hope I've answered the issue, maybe there's something I didn't cover. Basically you cannot be anabolic in terms of gaining muscle, but lose fat at the same time.. because the amino acids to be used in muscle synthesis will be sucked up by the gluconeogenesis pathway EXCEPT for leucine.

One more reason for us to pray to the almighty leucine.


So leucine is NOT used up in muscle synthesis? I thought the opposite was true?


No, he's saying that gluconeogensis (the creation of glucose from metabolites normally used in anabolic pathways [to create other shit])cannot use the branched chain amino acids to create glucose.

Thus those would be safe for use exclusively in the muscles.


If the body is in a negative energy state and enters gluco-neogenesis, what happens to muscle if there aren't enough amino acids available?

Having leucine available for building muscle doesn't help much if your body is tearing down the muscle to get much needed amino acids. Wouldn't it be better to have consumable amino acids in the blood stream so your muscle doesn't get used for energy?


Your body's always is states of anabolism and catabolism. When people talk about being in one of those states they're meaning the equilibrium has shifted that way, being more anabolic than catabolic= being anabolic to most folks.

If your body needs amino acids it'll break down something that has them.

Ideally you'd want to have enough AAs floating around that you dont' need to worry about muscle wasting and most of the time you do. The perk of having things like Leucine that aren't going to be used to replenish glucose is that even when you need sugar Leucine can still be put to work in the muscles.

Which I would imagine would reduce or prevent any real loss of muscle.


I get what you're asking; if the body is taking up AAs from the body, why would leucine be of any use.

I think you're being too specific because if you're looking to build muscle you'll have to eat protein (full spectrum of AA), and the point I was making with leucine is that it will ALWAYS be used in anabolic pathways.


If youre not eating enough food then youre losing muscle