I've seen cycles in my own interaction with food (and exercise), and the "big picture" has become more important than obsessing over having gotten "off track" for a meal or even a day.
The trick for me has been a consistent effort to bring things back to center... back to center... back to center.
For instance, I'm going to see family in Vegas this weekend. Will it be a dietary disaster? Probably, LOL.
Like another guy said, I can make informed choices---even in such a debaucherous environment... eat two cookies instead of eight, etc. This helps minimize "damage," as it were.
And like another gentleman referred to, making a lifestyle shift over time is the bigger goal. Stressing about whether or not I'm "on track" means that I'm forcing myself to live in an unnatural state... and I used to do that a lot. Over time, however, I've shifted more and more toward water, fruits, vegetables, lean meats, etc., on a regular basis.
Such a shift takes time and there will never be a "perfect adherence" to the ideal. And obsessing about such regimentation is in itself not so healthy. Finding balance and working toward a goal but allowing for human breathing room, however, seems a much more attainable---and ultimately, healthy---direction to strive for.
So if ya "cheat" or "fall off the wagon" or whatever you wanna call it, it's OK to say, "OK, that's done and over with," dust yourself off, and simply bring it back to center. Start again for today with the next beverage or food choice and just move on...