Dear 100 Hour Board,
I was wondering what would happen if you were hypothetically able to eat yourself. Would you grow twice as big, disappear, or stay the same size? I know this seems like a ridiculous question, but I have had it for years and no one had been able to answer it for me.
-Someone who has had this question for years
Turns out there is a condition under which people do eat themselves. It's called starvation. Well, to be more specific, it's called catabolysis, and is a condition of severe malnutrition/starvation. If you don't feel like reading that Wikipedia page I just linked to, basically when your body doesn't receive the necessary nutrients, it will start to break down its own fat and muscle cells. Your body literally eats itself when no other food source is available. This always results in your body getting smaller (except I'm pretty sure your stomach becomes distended), and often results in death. If your body gets to the point of breaking down your muscle, even with medical treatment, the effects can be irreversible (scary).
However, your question seems to be pertaining to the idea of hacking off chunks of your own flesh to consume via your mouth (after writing that, I just have to say, "Eww."), as opposed to what's described above. This would be very bad. Aside from the grossness factor, when your body is injured, it requires more nutrients (i.e. food) in order to heal. However, you would only be eating whatever had been cut off (so, not extra). Exacerbating this problem is the fact that energy is always lost in consumption. Thus, injury effects aside, you wouldn't be gaining as much energy as what you lost. So, if you were to actively cannabalize yourself, you would eventually disappear. Not immediately, mind you--only after dying a very gruesome death (of slowly cutting away more and more of yourself, and never getting enough to heal or even function at the level you had previously--probably your body would be forced into catabolysis too), and then decomposing. Which, I guess if you look at it that way, since all of us will die, all of us will disappear regardless of eating ourselves in the process.
P.S. After I finished this answer, Alta informed me that having a distended stomach is called kwashiorkor, and is caused by insufficient protein consumption (literally quoting her here). So, it's a symptom of malnutrition and sometimes occurs in conjunction with starvation, but not always. However, more common than kwashiorkor in starving people is marasmus, caused by overall energy deficiency. Marasmus is what makes people look super emaciated (like Holocaust survivors by the end of WWII). So if you're suffering from severe catabolysis, chances are you're also suffering from marasmus. Thanks, Alta, for giving us all this further light and knowledge pertaining to starvation.
If you tried to eat yourself too fast and sever an artery, you might die of blood loss within minutes.
If you take it slow, I think there's a good chance you'd get an infection and die long before you disappeared. Especially if you don't take an antibiotic while you attempt this.
Also, don't attempt this.