The answer is less about how often you go off plan and more about how far you go off plan (and if you are able to do anything to compensate for it).
When eating a meal that isn’t part of our plan, it’s tempting to say “Welp, this pizza is already off-plan, might as well get the side of fries and wine as well.” which then makes it even easier to say “Hey, I’m already off plan, I think I’ll go with dessert as well.” Sometimes the weekend spirals further the next morning when we say “Sure, waffles and mimosas at brunch don’t sound bad at all. After all, the weekend is kind of a bust, I’ll just get back at it on Monday.” Things can snowball pretty quickly once we’ve had our first bite of something off-program.
Instead of treating each day as though it were in a bubble, consider your week as a whole. Instead of having a day be either “on” or “off”, consider shades of gray. If you’re targeting 1500 Calories each day, rather than have five perfect days of 1500 Calories consumed and two off days of ???? Calories, consider your goal from a weekly perspective of 10,500 Calories (1500 x 7 Days). Decided to eat an extra 600 Calories of pizza on Sunday? Great. Now have 100 Calories less the next six days and you can still hit your goals for the week.
Next time you mindfully decide that it’s a good time to go off your nutrition program, ask yourself how far off you want to go before you start, and see if there is anything you can do on the days following (or even days preceding if you have advance notice) to balance things out. This approach will allow you to have your pizza, and eat it too!
To extra pepperoni,