Hi Johnnymo!

Yes, the induction phase of Atkins can lead to a lower potassium level in some people which is one of the main reasons that Dr. Atkins recommended supplements especially during that phase of the diet. Leg cramps can also be caused by low magnesium and/or calcium levels. The increased urination can cause you to lose more of those minerals than normal.
If you are taking any type of blood pressure medication, check with your doctor or pharmacist before adding supplements as some of them don't mix well with added minerals such as those above, but otherwise you can safely supplement with 99 mg and up to 400 mg. of potassium daily or switch to a potassium chloride salt substitute such as Nu-Salt to get some extra potassium. An extra calcium/magnesium supplement probably wouldn't do any harm, either.