With the cyclic ketogenic diet, initially it takes roughly 2 to 4 weeks (or so I've been told) before the diet becomes easier and you start ketosis. I'm assuming that in this time the body is using up all the carbs in the system before it has to go into 'fat burning' mode.

However regarding the 'carb up' on the weekend, which is an integral part of the cyclic ketogenic diet which allows you to 'refuel' with energy before a week of gym. Why doesn't the body then take another 2 to 4 weeks to go back into ketosis.

I assume it's partly to do with the fact that the body has to burn less carbs after the weekend than initially, but surely the body doesn't store that many 'ready to use' carbs...

What different is going on in the initial stage than after each 'carb up' weekend?

2 Answers 2


When you take out the cyclic part, and talk about ketosis by itself, it can help understand what's going on. Ketosis happens in stages:

  • Deplete the glycogen stores (usually takes 2-3 days). Until this happens, ketosis won't happen. This can be sped up by exercise.
  • Retool the metabolism to use ketones (usually takes 2-4 weeks, 3 on average). Ketosis will be happening from when your glycogen stores are depleted, but the body is not efficient at it.

Essentially, as long as you have glycogen, you have blood sugars that your body can use to keep your brain happy. Glycogen is the energy stored in your muscles and organs. When your blood sugar dips below what your brain needs (roughly 125g of blood sugar/day), your body releases glucagon. Glucagon is a catabolic hormone used to pull energy out of your muscles, organs, and fat cells. While your muscles and organs can burn fat directly, your brain cannot.

Once the reserve of glycogen is gone, and there is still a lack of sugars in the blood, the body starts producing ketone bodies. This process basically converts the fat to a substance your brain can use for energy. At the same time it's starting the gluconeogenisis which converts protein sources to blood sugars. This is why all ketogenic diets have a good amount of dietary protein. The body will process the dietary protein before the muscles/organs. Initially, the body will over-compensate and convert more fat to ketones than it needs. This is a happy time for losing fat. Once the fat is converted to ketones they are either used or urinated out--it won't be re-assimilated as fat. Over a period of roughly 3 weeks (2-4 weeks), your body adjusts so it is converting the right amount of fat to support its needs.

Increasing the demands for energy while in a state of ketosis may cause the gluconeogenisis to be the principle provider of energy. This is a bad thing, as the demands can quickly get to the point where the body has to resort to cannibalizing the muscle you are trying to build. This is why cyclic ketogenic diets were invented. It prevents the body from getting to the point of cannibalizing itself, while still keeping the fat burning benefits of ketogenic diets.

Once you "carb up", the body secretes insulin. Insulin is an anabolic hormone which triggers storing the energy in your muscles, organs, and fat cells. The good news is that the energy goes where it is needed most--which if you exercise will be your muscles and organs. Over-carbing will deposit the extra energy into your fat cells. The carb up replenishes your glycogen stores, which will help you in the gym.

  • Ah OK, thanks for your answer. So as I understand it the only difference in the initial stage is the fact your metabolism is being 'retooled' to learn how much fat it needs to convert. So does this mean after you 'carb up' the metabolism doesn't 'untool' itself, because the energy essentially gets used up straight away in the muscles? So what happens if you over-carb? Does it take another 3 weeks to be back again?
    – user3072
    May 31, 2012 at 19:42
  • Your body adapts to what you ask it to do. The re-carb does keep the metabolism from fully adjusting to the level it would on full ketosis, which works to your advantage. Excess energy (carbs/fat) will be put back in your fat cells. The ketosis is a good tool for remaining in a fat burning state most of the time. May 31, 2012 at 21:28
  • So say, hypothetically, you stopped following a ketogenic diet. How long would it take before your metabolism adjusts back to how it was before (the 'normal' metabolism) and so if you were to restart a ketogenic diet, you would have to undergo a 3 week induction again, where your metabolism 'retools' itself for ketosis?
    – user3072
    Jun 1, 2012 at 9:45
  • I've answered this before. But it depends on how you got your food. If you had highly processed sources of protein (protein drinks, for example) as your main source of nutrition, then two weeks of solid food (but still ketogenic) will help the stomach be ready for real food again. Other than that, 2 weeks bringing carbs back on line (probably best to spike it in one meal) will help the body deal with carbs appropriately again. Jun 1, 2012 at 12:50

From my understanding, which is admittedly basic, your body is producing new enzymes to more effectively mobilize lipids as an energy source during that two to four week period. Regardless of how much fat you put in before you have the necessary enzymes, your body can only process and use the fat at a certain rate. This is why it can be pretty horrible subjectively. You're basically running on empty during this period. Once the enzymes are generated, they are not totally abolished during short periods of high carbohydrate intake.

Please correct anything I've got wrong up there.

EDIT: So as it turns out the information above is mechanistically incorrect. Lipase is active pretty consistently in most healthy people (primarily during sleeping hours), the big shift is when your body/brain tissues decide to start using the products of lipolysis as their primary energy source, which only occurs when it doesn't have an alternative. The body's very stubborn about its preference for sugars, as their breakdown and use is simple and effective.

Sorry about my confusion. Here are links as requested:



  • It would be better to share the link from which you got to know this.
    – Freakyuser
    Mar 31, 2014 at 6:13

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