Ketosis is merely a byproduct of the body's breaking down fats fot fuel. No matter how you reduce your body fat, except liposuction, the long chain fatty acids are broken into ketones for burning. If you stay on a low carb diet, your body may get more efficient at this process and you may not show the higher concentrations of ketones in the urine, but the metabolic advantage of low carb does not disappear. Atkins, in his practice, did not use urine to measure ketones, but the breath.
If carbs are available in sufficient quantities, the body will not break into it's fat reserve, which is why high carb diets require such drastic calorie reductions to work. Also, without the carbs, the insulin cycle doesn't get strated, making it hard to gain body fat. Low carb, because it contains adequate protein, does not cause the body to break down muscle tissue to make glucogen. Tests have shown that muscle loss is much less in low carb diets.
Ketoacidosis is the breaking down of muscle tissue and it can be fatal to diabetics, ketosis is the breaking down of long chain fatty acids nto ketones, which is a preferred fuel for the brain and other organs.
More info is available in Dr. Mary Enig's book "Know Your Fats." and on the www.westonaprice.org site. Nyah Levi