This might sound harsh, but you need to stop making excuses for yourself.
It sounds like you have the knowledge on "how to", but wish not to use this knowledge for yourself.
Living a "healthy lifestyle" is a habit. Sounds like you have developed some pretty bad habits.
In regards to eating out when on work conferences etc, you just need to do the best that you can do. That means things like not piling on the sauce, eating more lean meats, eating less fries, have 1-2 beers but there is no reason why you need to have 10.
I might be wrong, but I would think that people in your expertise of work would be more impressed with someone who looks like they are in decent shape and have confidence in themselves, opposed to the person who is overweight and likes to drink gallons of beer.