These are the basics, yes, but it's not that simple. To me, IF means: from 8PM to noon next day drink only water and (if you like) one black coffee in the morning. Then, from noon until 4PM eat just proteins, healthy oils & fats and raw vegetables - this is crucial, absoultely no carbs! Finally, from 4PM until 8PM eat everything.

That way you keep insulin under control for the 20 hours (out of 24). Your concentration and focus will increase very soon.