A recent news story implied that going on a low carb diet causes potassium deficiency. That is not the case! Low carb diets definitely do not affect potassium levels.
What is potassium? Potassium is a mineral that helps your electrolytes in your body stay balanced. It is important in your muscles and nerves. It also helps in proper metabolism.
Because of that, every low carb diet I know of instructs you to take adequate vitamins. Given the types of foods most US residents eat, that is a wise decision! Most people are deficient in vitamins based on their normal way of eating. That is, most people on a fast food diet aren't getting enough potassium in that normal eating style. Since low carbers are taking vitamins to begin with, no matter what else you ate, if you followed a low carb diet properly, you wouldn't be deficient in any vitamin.
Where do you get potassium from in nature? First, you get it from meat. This includes beef, chicken, ham, pork, turkey, fish, oysters, lobster. Etc. Obviously people on a low carb diet should get tons of potassium in their diet - far more than most other people.
Next, you get potassium in your vegetables. This includes asparagus, tomatoes, squash, cauliflower, mushrooms, and spinach. All of these are things encouraged by low carb diets for you to eat - even in the first two weeks of the diet! Low carbers tend to eat far more vegetables than the average pasta-and-fries person.
A person eating a healthy low carb diet would not have any potassium issues if he or she were actually following the diet properly. If the person was not taking vitamins and was choosing to only eat lettuce and cucumbers, something hardly recommended by any diet, then they could have a problem. But they would have caused their own problem by not following the diets as laid out by the countless books and websites around today.
Meat, Protein and Absorbing Calcium Myth
Low Carb, Atkins and Kidneys
Gout, Obesity, Protein and Low Carb
Lisa Shea's Library of Low Carb Books