I considered myself fit, albeit too sedentary, when I was diagnosed with T2 Diabetes as the result of a routine medical one year ago (I had no diabetes symptoms).
I cannot say that I feel markedly healthier as a results of being on a low-carb diet (and reversing my diabetes) for the past year. I have noticed that I am sleeping better, but I attribute that entirely to taking much more daily exercise than I did, pre-diagnosis. I did lose eleven kilos, but I was not (medically speaking) overweight in the first place and now hover close to "underweight." The beer paunch disappeared, but that's just "by the by." I don't feel any more "energetic."
Having said all of the above, reversing a serious chronic disease using diet-only was, and continues to be, an enormous benefit (and came as a huge surprise, perhaps even more surprising than the T2 diagnosis itself). That is quite enough for me!!!