The question arises because to me it seems not worth eating. It is worth eating when it comes to the chance of negative effects?
I found the answer on the Pixel Dungeon Wiki and thought I would share it as a Q&A style answer.
TL;DR It is better to cook the meat in on a fire, or freeze it before eating. If you can't, eat it over water to reduce the odds of physical damage.
Mystery meat is dropped by sewer crabs, cave spinners, scorpios and giant piranhas. Eating mystery meat is dangerous, because it might have the following effects:
Burning 1/5 20 %
Rooted 1/5 20 %
Poisoned 1/5 20 %
Slowed 1/5 20 %
No effect 1/5 20 %
Because of this, it’s a good idea to eat it over water in case you catch fire. Mystery meat can also be harmless, but the chance is 20 % only. The only way to make mystery meat safe is to cook it by throwing it onto a fire (turning it into a chargrilled meat) or to freeze it (tuning it into Frozen carpaccio). Mystery meat, chargrilled meat and Frozen carpaccio are half-value foods; if you are starving, they will only return you to hungry rather than completely sated.
To add, Mystery Meat is never worth eating. The chance that you will get a potion of Liquid Flame, a Firebloom Seed, Wand of Firebolt, or run into a Firetrap are highly likely.
In the case of Liquid Flame: find the barricade it's intended to be used at and drop the meat next to the barricade before setting it on fire.
For Firebloom: drop the meat in a door frame and then plant the Firebloom on it and then throw another non-burnable item on it to cooking everything.
The chance you will get any of these items is much greater than the chance of "No Effect"
Also, even if you're on water your scrolls have one turn to still possibly burn up. Drop your scrolls (preferably on water) when there is a risk of fire.