works but its not sustainable

The basic essence of this diet is to cut the carbohydrates and mostly focus on eating protein. I tried this because some of my friends had some effect with this diet. I tried for about three weeks and lost five pounds. What I liked about this diet was that compared to others, I didn't feel that hungry while I was doing it. But because you eat so little carbohydrates, I think your brain function gets slower. This was a big problem for me because I have a job where I need to constantly use my brain. And it is very difficult to sustain the weight lost because once you start back on the carbohydrates, the weight comes back as well.