Why does muscle shrink from absence of lifting but fat stays when eating in maintenance?
In: Biology
So our bodies are generally optimized to not starve. This means getting rid of energy-expending things we don’t use, and hanging on to energy if we ever have a surplus.
Muscle is an energy-expending tissue; the more you have, the more it burns, even moreso than just “added weight.” So if you don’t “prove” to your body that you NEED that muscle through exercise, it will “recycle” the extra muscle to conserve energy.
Other animals, like apes, do not lose muscle as easily as us. That’s why gorillas and chimps are so jacked compared to us. But our species evolved to move efficiently over long distances, so our bodies shed excess expensive tissues like muscle very readily.
Fat, on the other hand, STORES energy. So your body doesn’t want to get rid of it – unless it has to. It is saving up that energy for a day you might not be able to otherwise get it.
This question is like asking “why does a phone turn off its screen after a while of inactivity, but the battery doesn’t drain when plugged in?”
Muscles consume energy to exist, so the body wants to keep smallest required.
Fat stores energy, the body is only going to use it when it needs more energy.
Why does muscle shrink when doing *nothing* to maintain it, but fat stays when doing *something* to maintain it?
Muscle shrink from absence of lifting. Fat stays when eating in maintenance.
Muscle stays when lifting in maintenance. Fat shrinks from absence of eating.
It’s a weird question that should be pretty self explanatory. “Why I’m moving faster when walking 3 mph than running 0 mph?”.
Fat is an energy storage system that you body wants to have. The body will only use the stored energy when it needs to, so when you are not eating in a maintenance.
Muscles are tools that the body grows as needed. If the tools are not used as much, then the body will slowly get rid of them to save energy.
fat is way way way more useful than muscle to almost every human that existed and evolved over millions of years except the last maybe.. 100 years when food for plentiful and cheap
Will add to these great answers that there are many functions of fat beyond just energy storage. There are multiple types of fat that have various functions that help us survive. There are fat cells essential for breastfeeding, warmth generation, energy storage, signaling to other body systems, etc. Even the white fat, that is likely what is meant in this question, can adapt to help us stay warm in cool climates, for example. It’s useful to keep fat around in case of emergencies but if you aren’t using the muscle, it’s less beneficial to keep bulky muscle just in case.
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