Originally Posted by John Barky
so it's maybe a calorie thing?
has anyone similar experiences?
It could be a calorie thing. I IF, and actually my metabolism began to slow and if I ate what I would normally eat (around 2,500 cal give or take a couple hundred) I would actually gain weight. My body's "need" went down due to IF to about 1,800-2,000 a day and I was at around 40% carb intake, which isn't exactly low carb.
It can also very much be a macronutrient thing, as your body is switching itself to using protein for fuel rather than carbohydrates. Here is an easy test now that you are 3 weeks in, go find some good organic chocolate and eat about 1/2 the bar. If you get an enormous sugar high, you have definitely switched. I found after about 3 months of doing IF that I could actually feel the thermogenic effect of protein and the sugar rush from even an apple. It is wonderful to be that in tune with your body.
Experiment, this is a fun and exciting thing to do, and a chance to really learn about what makes you run at top performance. Since everyone is different (even though we really are 99% the same) you can tweak your diet for great success.