Admittedly with little research I tried out a low-carb (more like no-carb) diet (of my own invention). I ate pretty much only meat and green leafy vegetables. I was ravenous all throughout. I remember eating large amounts of meat and still feeling like I was starving. It was hard to concentrate on pre-exam days because I was so hungry.
Not trying to be snarky, but I suspect this is where your problem was.
One of the most commonly reported side effects of typical low-carb diets is appetite suppression. Better focus after the first couple of weeks is pretty common as well.
I will note that while I think low carb diets work, I'm also firmly of the belief that, in terms of weight loss, they're still caloric deficit diets at the core. It's just there are a few other things going on metabolically -- including the appetite suppression -- that tend to make them easier for a lot of people.