I do intermittent fasting since a couple of months, initially started with 16:8 and then moved to 18:6 after the first 4 weeks.

It took around 3-4 weeks until I noticed results which seems in line what I was told by others.

What stood out beside the weight loss (I was very close to my ideal weight anyway) was my ability to concentrate. I noticed a huge improvement after around 5-6 weeks. When I try to come up with the right words in a conversation it feels I have immediately in mind what I want to say.