I don't understand muscle loss while dieting

jessica22222

From my understanding, your body stores fat for energy. When you eat at a deficit your body uses your fat stores to sustain your energy.

Why would your body use your muscle mass? This doesn't make sense to me. I thought the fat was the energy source not the muscle.

brianpperkins

The major part of it is that muscle building and maintaining is a resource intensive process and the body doesn't have enough of what it needs to fully complete that process while in a deficit. Activities tear down muscle, the body prioritizes which muscles get the limited resources, and skeletal muscle loses out to things like the heart in that prioritization.

AJ_G

There is an energy cost associated with maintaining muscle mass at it's current state. If you are in a negative energy balance (calorie deficit), the body will not maintain the same muscle mass because of the lack of energy required to maintain it. This is the same reason you will not build muscle mass in a negative energy balance, because there is an even higher energy cost associated with growing muscle.

cwolfman13

brianpperkins wrote: »

The major part of it is that muscle building and maintaining is a resource intensive process and the body doesn't have enough of what it needs to fully complete that process while in a deficit. Activities tear down muscle, the body prioritizes which muscles get the limited resources, and skeletal muscle loses out to things like the heart in that prioritization.

AJ_G wrote: »

There is an energy cost associated with maintaining muscle mass at it's current state. If you are in a negative energy balance (calorie deficit), the body will not maintain the same muscle mass because of the lack of energy required to maintain it. This is the same reason you will not build muscle mass in a negative energy balance, because there is an even higher energy cost associated with growing muscle.

to add to these, you can only oxidize a finite amount of fat over a 24 hour period as well.

WBB55

Basically, your heart, veins, digestive system and respiratory system have muscle cells that must have what they need 24-hours per day to continue keeping you alive. If there isn't enough protein, required minerals, vitamins and other components required to rebuild the heart muscles, your body will break down your glutes or whatever other skeletal muscle to get to the amino acids, etc. it needs to keep you alive. It's not breaking down the muscle for "energy" for the most part (though there is a little bit of energy stored in muscles it could use). It seems from charts I've seen that without resistance weight lifting, long-ish term weight loss will be 20-33% lean tissue (including bone, tendons and other lean tissue besides muscle).

Kalikel

You need more muscle when you're bigger. Your body naturally adds muscle when it needs it and naturally takes it away when you don't. Supporting all that weight when you're fat - it works the legs!

When I started using the leg machine, I had no difficulty moving anything under 140 and could go higher, with effort. Then I quit the weights (because I hate them and not because I should've.) When I went back to it, 80 pounds was harder than 160 had been. My legs were lighter, but I'd lost muscle, too.

It just happens. If you don't use the muscles, they get smaller and weaker. If you use them, they get bigger and stronger.

That's why people who lift weights build muscle - the body realizes it needs more to do the heavy lifting.

evileen99

Your body is continually breaking down s nd rebuilding tissue-- muscle included. As others have said, it requires calories to maintsin muscle, and in a deficit, your body is looking to cut back on any unnecessary tissues that use calories. If you lift weights, it signals your body that a lot of muscle and it will keep making that muscle.

arb037

I see a lot of " myth" and misinformation so am going to put links down so you can read and make up your own mind.

http://www.bodyrecomposition.com/fat-loss/size-of-deficit-and-muscle-catabolism-qa.html/

http://forums.lylemcdonald.com/showthread.php?t=11223

http://www.bodyrecomposition.com/fat-loss/setting-the-deficit-small-moderate-or-large.html/

http://www.bodyrecomposition.com/fat-loss/permanent-metabolic-damage-qa.html/

http://www.bodyrecomposition.com/fat-loss/adding-muscle-while-losing-fat-qa.html/

The body can metabolize 31 calories per lbs of fat on the body per day. So given "adequate" protein and lifting heavy weights, you should not lose much if at all LBM.
With that an example would be if you had 30lbs of fat X 31cal/per = 910 calories can be burned per day from fat stores, so if you exceeded that in a deficit, you would probably start to suffer LBM loss.
This is why peoplw who are obese can stand to run greater deficits and lose faster, but when we get smaller the "excess" fat is not as much so the loss has to progress much slower.

brianpperkins

The 31 calories per pound of fat is a theoretical max ... not a planning factor in the real world.

stevencloser

brianpperkins wrote: »

The 31 calories per pound of fat is a theoretical max ... not a planning factor in the real world.

As far as I've heard (but without sources provided), the number got revised to 22 even.

DeguelloTex

brianpperkins wrote: »

The 31 calories per pound of fat is a theoretical max ... not a planning factor in the real world.

So build in a cushion. It makes a lot more sense than trying to say a 4'11" woman and a 6'9" man with 25 pounds to lose should be losing at the same rate, like the often-repeated brackets posted here do.

brianpperkins

DeguelloTex wrote: »

brianpperkins wrote: »

The 31 calories per pound of fat is a theoretical max ... not a planning factor in the real world.

So build in a cushion. It makes a lot more sense than trying to say a 4'11" woman and a 6'9" man with 25 pounds to lose should be losing at the same rate, like the often-repeated brackets posted here do.

Just how do you propose to build in a cushion when the number is theoretical and the subjects in the real world haven't done the medical studies required to identify the amount of actual excess fat they are carrying? There is a difference in using a site based upon the center of the bell curve when it comes to safe loss rates, such as MFP, and going for the max possible under controlled and supervised medical conditions.

DeguelloTex

brianpperkins wrote: »

DeguelloTex wrote: »

brianpperkins wrote: »

The 31 calories per pound of fat is a theoretical max ... not a planning factor in the real world.

So build in a cushion. It makes a lot more sense than trying to say a 4'11" woman and a 6'9" man with 25 pounds to lose should be losing at the same rate, like the often-repeated brackets posted here do.

Just how do you propose to build in a cushion when the number is theoretical and the subjects in the real world haven't done the medical studies required to identify the amount of actual excess fat they are carrying? There is a difference in using a site based upon the center of the bell curve when it comes to safe loss rates, such as MFP, and going for the max possible under controlled and supervised medical conditions.

Call it 20 calories per pound per day, for example.

Why does someone need a medical study to determine actual excess fat? Reasonable approximations -- just like with intakes and burns -- can be used.

I'm not saying go for the max possible; "build in a cushion" pretty much shows this.

daniwilford

I am a little confused here. If I, being obese, use the equation provided by @arb037, substituting the revised 22 suggested by @stevencloser, I could eat a VLCD composed of almost pure protein and still lose only fat?
ETA: Warning this is only theory, not advise or my plan at all.

IsaackGMOON

jessica22222 wrote: »

From my understanding, your body stores fat for energy. When you eat at a deficit your body uses your fat stores to sustain your energy.

Why would your body use your muscle mass? This doesn't make sense to me. I thought the fat was the energy source not the muscle.

Your body is an efficient machine.

If it has something which isn't being stimulated, and is 'spending' calories in keeping that living tissue alive, it will use it as energy to reduce the amount of energy it has to expend.

WBB55

daniwilford wrote: »

I am a little confused here. If I, being obese, use the equation provided by @arb037, substituting the revised 22 suggested by @stevencloser, I could eat a VLCD composed of almost pure protein and still lose only fat?
ETA: Warning this is only theory, not advise or my plan at all.

Essentially that's similar to what they do with the liquid diets at medically controlled weight loss clinics, if what I've seen from some of my family members is typical. And I don't think they keep people at VLC for more than 12 weeks or so because the chances of malnutrition start climbing at that point.

DeguelloTex

daniwilford wrote: »

I am a little confused here. If I, being obese, use the equation provided by @arb037, substituting the revised 22 suggested by @stevencloser, I could eat a VLCD composed of almost pure protein and still lose only fat?
ETA: Warning this is only theory, not advise or my plan at all.

You'd probably still lose some muscle because of the way the body works, it just wouldn't be explicitly scavenged as it would be if your deficit exceeded what could be provided by your fat stores.

brianpperkins

daniwilford wrote: »

I am a little confused here. If I, being obese, use the equation provided by @arb037, substituting the revised 22 suggested by @stevencloser, I could eat a VLCD composed of almost pure protein and still lose only fat?

In a theoretical vacuum, yes ... in the real world, highly doubtful. The body never burns just one source for energy ... it is a constant shifting of ratios of various fuel sources.

daniwilford

Thanks to OP for asking the question and all others for the informative answers. I am very interested in maximizing my fat loss while retaining muscle. I will not be going for maximum for now but as I get closer to goal it is good to know the average limits.