Why do we lose lean muscle when on a deficit?

ColetteM6

Does anyone know the science behind this? I cannot wrap my head around the fact that my body will chew through muscles before the 175,000 (!) spare calories that I'm already schleppinng along as fat.

TheRootofGroot

Lost about 20 pounds and not one of it muscle.
It's all in how you do it.

My trick is high protein, and high volume weightlifting.

KetoneKaren

@smarieb306 This might answer some of the questions you have: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3970209/

jessiethe3rd

To boil it down...

Muscle and fat both get burned. If you go too fast (read reduce too many calories) then more muscle gets burned up. If you do not lift muscle gets "chewed" up and your metabolism suffers as your body thinks it is starving. Thousands of years of evolution made us this way for obvious feast or famish style diet humans have had.

That's the basics in laymen's terms.

determined_14

As I understand it, muscle is metabolically "expensive"-- it takes more calories to maintain than fat. The body wants to run as efficiently as it can, just in case all the food runs out, so on a deficit the first thing it wants to get rid of is all that calorie-demanding muscle.
By eating sufficient protein and lifting weights, you can convince your body that you still need that muscle, and burn more fat instead. You might still lose a little, but if you're following a good strength program, the muscle you keep will become so much stronger and more efficient that you likely won't even notice. Also, when you lose that layer of fat over top, your muscles will look much more prominent.

four_bumblebees

All metabolic processes are constantly running, but the equilibrium between the forward and reverse reactions shifts. For example, when you haven't eaten for several hours, the tendency is to break down fatty acids to get energy. However, because of the chemistry and the way we evolved, there is still a tiny bit of fatty acid synthesis going on, though the net result is fatty acid breakdown. The reactions for breaking down and building up muscle are also running at the same time, but eating in a deficit favors the breakdown reactions. The larger the deficit, the more you favor breakdown. You preferentially break down fatty acids, but because our bodies can't (reasonably) stop the muscle breakdown reactions (it would be very bad if we did anyway), there's still a little bit that has to happen when eating in a deficit. (Source: I just took a class on the biochemistry of metabolism)

LivingtheLeanDream

Its virtually impossible not to lose muscle along with the fat, too agressive a deficit will really see the muscle being lost as well, so slower loss will mean less muscle loss. Protein does help as does resistance training with keeping muscle loss to a minimum.

SideSteel

RunRutheeRun wrote: »

Its virtually impossible not to lose muscle along with the fat, too agressive a deficit will really see the muscle being lost as well, so slower loss will mean less muscle loss. Protein does help as does resistance training with keeping muscle loss to a minimum.

It is not impossible to mitigate muscle loss depending on the deficit size, amount of available body-fat, and training experience of the individual.

extra_medium

jessiethe3rd wrote: »

To boil it down...

Muscle and fat both get burned. If you go too fast (read reduce too many calories) then more muscle gets burned up. If you do not lift muscle gets "chewed" up and your metabolism suffers as your body thinks it is starving. Thousands of years of evolution made us this way for obvious feast or famish style diet humans have had.

That's the basics in laymen's terms.

I think the question she's asking is why would the body prioritize burning muscle over fat from an evolutionary/survival point of view.