Hi there,

if you decide to do Atkins or follow any other kind of low-carb eating plan, the best advise is for you to read the book first - it's not hard, but important to know what you are doing.

And to answer your question:

Atkins starts out with a 2-week introductory period during which your carb intake should be limited to 20 grams of carbs per day - and those carbs should come mostly from certain salads and vegetables.

I am not sure how many carbs one slimfast has - but I'm guessing more that those 20 - so no, combining those two seems to defeat the purpose of both.