When You Fall Out Of Ketosis, This Is What Happens To You
If you're on the keto diet, eliminating most carbohydrates from your diet, your body will eventually go into ketosis, where it burns fat to make ketones to use for fuel rather than carbohydrates (via WebMD). But if you stop following the keto diet's strict protocol, even for a short period of time, your body will quickly fall out of this fat-burning phase.
While the keto diet may help you lose weight as your body begins to rely on fat as fuel, it is rarely a good short-term solution, since quitting the diet and reintroducing carbohydrates can result in weight gain that's just as rapid as your weight loss was (via LIVESTRONG).
There's more bad news as well: Just as there was a transition that caused you to be tired and irritable as you cut out the carbohydrates, reintroducing them may make you irritable and tired as your body shifts back to using them. You may also feel bloated.
Why does that happen?
"As soon as you introduce carbohydrates to your system, the body will use them preferentially for fuel," dietitian Ginger Hultin told Men's Health. Be warned: A single day of high-carb eating can knock you out of ketosis, so if staying in the fat-burning zone is important to you, skip that cheat day pasta dish and find a keto-friendly substitute instead.
Once you're out of ketosis, it can take one to three days to drop back in, depending on how many carbohydrates you ate: Your body essentially has to use them up and shift back into ketone production before you're officially in ketosis. That means you may even suffer the unpleasant side effects that came when you started the keto diet, including headaches, fatigue, and all the other symptoms of the "keto flu" (via Men's Health).
If you decide to transition off of the keto diet but want to skip the impending weight gain and other negative side effects, the Cleveland Clinic recommends continuing to keep your simple sugar consumption low, and reintroducing carbohydrates in the forms of more bean-based pastas, along with plenty of vegetables and water.