Theres no bodily function that says, this diet will not work.

The amount of energy your body burns depends on your metabolism.

When you diet, when anyone diets, unless they weight train they WILL lose muscle as well as fat. Most people have trouble keeping the weight after dieting because of this, they have lost muscle mass.

Metabolism is directly related to muscle mass, therefore by losing muscle when dieting, you also lose a fraction of your metabolism. When people stop dieting and resume the lifestyle they had before dieting, they quickly regain the weight they have lost because their metabolism is lower than it originally was. The only problem now is that the weight gained back is probably 100% fat. Making it even harder to diet and lose the weight again( Your problem).

I would advise either starting a light weight training routine or cardiovascular training.

The diet will still work for you, regardless of your past habits.

The basic premise is this: carbs lead to insulin in your blood, insulin tells your body to store fat in fat cells. Insulin also will prevents your body from releasing or burning fat from fat cells. By reducing carbs you allow your blood insulin level to go down, which enables your body to burn fat. This is a simplification, but a workable model of what's going on.

However, everyone's carb tolerance is a little different. Atkins himself said as much. So experiment with what works for you, and keep experimenting because sensitivities change the longer you're on the diet. You'll find a regimen that will work for you.

Good luck!

Atkins will not work if you are doing it "off and on" That is because there is no such thing as doing Atkins off and on. You have to stick with it in order for it to work. However, if you quit it, you can always start back on induction and there is no reason that it shouldn't work again! Just start back at square one. None of us are perfect and it is easy to fall off of the wagon!