So far, we have not had a single client who complied 100% to their meal plan for the entire time they were keto.
Whether it is a holiday where they could not turn down a family recipe without causing a feud, a particularly rough day at work, or a ray of light striking a Dunkin Donuts just so in the early hours of the morning, virtually everyone will go off keto at some point. For some people this is on the first day of the diet, and for others after many weeks of powerful self-discipline. It is invariably followed by a confession to us, the Keto Police (actually, we frequently tell people that we are not the keto police, but the contrite emails continue apace).
Keto is significantly different than other diets in the sense that “cheating” will alter your metabolic state in a measurable way for hours or days afterwards. On a calorie-restricted diet with high carbohydrates, one day of going off-plan will likely just stop your weight loss for the day, but aside from a sugar coma, it will not change much in your body. Being in nutritional ketosis is rather unforgiving: either you are, or you are not.
Mark Sisson, the paleo guru who first brought the then-weird idea of skipping grains to the internet masses over a decade ago, deals with the problem of going off-plan by planning to go off-plan 20% of the time. While his Primal Blueprint contains a lot less carbohydrate than the Standard American Diet, it is not meant to be ketotic by default.
We advise that people do not plan to go off keto on purpose, and then we expect to help them deal with the consequences when we do.