Attitude and awareness are ALWAYS key.
The LOGIC: I need to finish all the food on my plate, because "there are starving children in Africa".
The SOLUTION: Most of us had that ingrained in our heads when were younger, but cleaning your plate is not going to solve the world hunger issue; what it will do is add inches to your hips, if anything. So never eat just because it's there, only eat when you're hungry!
If you want to help with world hunger, get involved with organizations that help with that cause.
The LOGIC: It's a special occasion.
The SOLUTION: Even it's your birthday or anniversary, eating a big piece of cake will set you back. However, don't deprive yourself; instead have a small portion without feeling guilty.
The LOGIC: I deserve it.
The SOLUTION: If you've had a particularly bad day, don't let food be your compensation (YOU KNOW who I'm talking to here:). Instead treat yourself to something other than food, such as a nice massage, a good book, or best of all, a walk (alone or with a friend:).
Be aware and adjust that attitude as needed!