Abstinence is hard to figure out in the beginning. The simplest way to look at it is "refraining from compulsive overeating". Most of us need a concrete diagram of what this looks like so that we can attempt to do it, and be honest with ourselves about if we are doing it.
When I first came to program, my abstinence diagram was 3 meals + 1 snack with nothing in between. My goal was to teach my body to NOT eat between the meals. What I ate at those meals and how much I ate was not important. What was important was that my brain and body had to learn to trust that it wouldn't starve if I didn't eat for 4 hours in a row. After a month of that, I began to feel comfortable with it, and I became willing to add some other things to my abstinence.
There's an excellent OA book titled "Abstinence". It has people's stories of what abstinence means to them.
Yes, abstinence is key. Nope, we can't recover without it-- Can an alcoholic recover without maintaining sobriety?