Bake those potatoes
Potatoes are a rich source of potassium (as shown by the chart in this post): one potato has 1081 mg of potassium, almost as much as a cup of raisins (1089 mg). A banana, generally thought of as a good source of potassium, has 594 mg. And potassium, as explained at the link, is important for building muscle.
But if you cube the potato and boil it, the minerals are tossed out with the water. If you must boil potatoes, use the water as soup stock or the like. Obviously, if you are cubing the potatoes to cook in a soup, the minerals are not lost; they just go into the soup. The “loss” occurs only if the cubed potato’s cooking water is discarded. Here’s the story:
Cubing potatoes can reduce boiling time, but it also reduces mineral content by as much as 75 percent. That’s one conclusion from a study by research geneticist Shelley Jansky and plant physiologist Paul Bethke at the ARS Vegetable Crops Research Unit in Madison, Wis.
Jansky and Bethke subjected six potato varieties to various methods of preparation, and then ran a mineral analysis for potassium and 10 other minerals. They found that cubing or shredding potatoes prior to boiling resulted in significant potassium reductions.
This could be a good cooking strategy for potato fans hoping to reduce potassium intake, such as dialysis patients. But individuals who want to get the highest nutritional bang for their buck would be better off boiling their potatoes whole.
Jansky and Bethke also examined the effects of leaching the potatoes—letting them soak in water overnight. Their results showed that leaching had no significant impact on potassium reduction, in contrast with conventional wisdom.