I have to answer the OP's question about switching to a calorie-restricted diet with a question: Why would you want to? If you follow Atkins as it was designed, you will (re) discover the joys of feeling full and satisfied and eating a wide variety of foods in the right amounts for your body. You just need to count carb grams, which is so much simpler than counting calories. At the same time you train yourself to stay within a certain carb range, you also train yourself to stay in a certain calorie range. So if you embrace a low-carb lifestyle for life, it's a different path to the same goal - only more sustainable IMO.

I had a similar experience to Janet's, several times over: Weight Watchers, McDougall/Ornish, "whole foods plant based," "Mediterranean" - all with ample weight gain and failing health. Every body's different, but high carb low fat (automatically very low calorie) has proven to be an epic fail for me many times over.

Simply put, to paraphrase Dr. Atkins himself, the only way to keep the weight off is to keep doing what you did to lose the weight in the first place.

There is one food movement I've tried and like very much which you could switch to or incorporate into Atkins: paleo or primal. You can eat higher carb but whole foods in more abundance and maintain your weight and health with the right balance for you. Atkins is now marketing "Atkins 100" which is essentially the same thing provided you choose whole foods.

Of course, you could try Weight Watchers if you think that suits you better as it encourages whole foods and watching your fat and calories. Different strokes for different folks ... I can think of a couple of people who are lifetime members of Weight Watchers, and both were always naturally thin to begin with.