All diets make you lose weight – if you are able to keep at them, that is. But Nutrasystem diet is one of those few that make you feel fit, too. And, it certainly is not hard to keep at it either. A lot of science has gone into planning Nutrasystem Diet.The diet plan works on the Glycemic index principle, which is based on the levels of sugar present in your blood at all times. It ensures that you lose weight, but do not lose your energy levels or efficiency. In fact, you have higher and more evened out energy levels through the day. Quite naturally, this ensures that you are always fitter and more efficient.