I don't like this kind of advice, only because it sets people up to fail. If your definition of "success" is not cheating, not once, ever, for 90 days, 99% of people will fail that. Half within the first couple weeks. And if you've failed your goal such that it's 100% unattainable now, what's the point of continuing at all? What's the point of setting another 90-day goal you'll also fail at?
This might help for people with a very small, specific goal in mind - lose n pounds or y% body fat by a certain event - and who are already pretty strong and consistent mentally. But if you are trying to lose weight to look better or not have a heart attack at 40, it's not a sustainable way to approach things. It's much more sustainable, and healthier, to focus on small habits you can add over time.
If you eat fast food four times a week and have five regular cokes a day, you're much better cutting that to three sodas a day and stopping there than you are eating kale salads and protein shakes for a couple weeks before going right back to where you were. And cutting a couple sodas a day is much easier to boot.
This might help for people with a very small, specific goal in mind - lose n pounds or y% body fat by a certain event - and who are already pretty strong and consistent mentally. But if you are trying to lose weight to look better or not have a heart attack at 40, it's not a sustainable way to approach things. It's much more sustainable, and healthier, to focus on small habits you can add over time.
If you eat fast food four times a week and have five regular cokes a day, you're much better cutting that to three sodas a day and stopping there than you are eating kale salads and protein shakes for a couple weeks before going right back to where you were. And cutting a couple sodas a day is much easier to boot.