How Long Does it Take to Get into Ketosis?
Short Answer: 2-7 days
In order for your body to get to the point where it is breaking down stored fat into ketones for fuel, it must first use up all stored sugar. The body stores excess sugar in the muscles in the form of glycogen. It is stored there to give the muscles access to a quick source of energy should the need arrive. You must first deplete the glycogen so the body is forced to use fat for fuel instead.
There is about 2-3 days worth of sugar stored in your muscles so if you keep your carb intake at around 20g a day, you should deplete those stores within 3 full days. You can speed up the process by either fasting or exercising. The fasting will keep the body from creating new sugar from food intake and the exercise will cause the body to burn off the sugar faster.
If you are using a ketone tester, you should start seeing a ketone reading by the third day and start seeing them increase over the course of the next 2 weeks to a month. As your body begins to use ketones more efficiently, you should see ketone levels drop to right about .5 mM can go as high as 5 mM.
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