Although our diet is considered a medium to low calorie diet, our dieter’s bodies are actually registering “more calories” than they likely were prior to going into ketosis. Why is that? They are burning their own fat stores for energy. When we shift energy systems, specific enzymes need to be made in order to utilize the ketone bodies produced from burning their own body fat.
This process takes typically about 2 weeks, and after 3 weeks the enzymatic processes are getting completely set in place so that they are able to use 100% of those ketone bodies as fuel. During this critical period when your blood sugar begins to drop, your muscles will begin to go through the process of gluconeogenesis (a process that makes glucose to put back into your blood stream).
If you increase your energy demands by exercising to vigorously during this time, this ramps up gluconeogenesis and risks tapping into your muscle mass for fuel. WE WANT TO AVOID THAT AT ALL COSTS!
This is not a typical “calories in, calories out,” balanced diet. This is all about hormones and metabolism. After the 3rd week, dieters are able to resume physical activity and exercise.