I have a recipe that calls for mashed potatoes. It suggests cubing the potatoes before boiling them, to save time. Wouldn't the potatoes lose a lot of nutrients that way?
Yes, your instincts are right on the money.
Potatoes are great source of potassium, which helps regulate the effects of sodium and other minerals to stabilize blood pressure, regulate the heartbeat, contract muscles, and offer other health benefits.
However, many people don't get enough potassium in the diet. The recommendation for adults is between 4,000 to 4,700 milligrams a day, and, because it's excreted through normal kidney function, it needs to be replenished regularly.
With potatoes the most popular vegetable around, that should be relatively easy to do. According to the U.S. Department of Agriculture's Nutrient Database, a large, 13 oz. raw potato with skin has 1,553 milligrams of potassium, and, according to the Economic Research Service, Americans on average consume 135 pounds of potatoes a year. Still, many Americans don't get enough potassium in their diets.
A study published in a recent issue of the Journal of Food Science examined different cooking methods for six varieties of potatoes. Researchers found that potassium was reduced by about 50 percent when potatoes were cubed before boiling compared to the content before cooking. In addition, the cube-and-boil method affected other nutrients, too. About 35 percent of magnesium was lost, and 25 percent to 30 percent of zinc and manganese were lost.
Previous research cited in the study showed that nutrients --in potatoes and other vegetables -- are protected if they're cooked by baking, roasting, microwaving or steaming. If you boil potatoes and want to retain nutrients, boil them whole or cut them into large chunks, not small pieces.
On the other hand, people with reduced kidney function can't consume much potassium. For those folks, cutting potatoes into small cubes or thin slices before boiling is just what the doctor ordered.
In the past, doctors have recommended that kidney patients also "leach" potatoes of potassium by soaking cut or shredded potatoes in water overnight, in the refrigerator. However, the Journal of Food Science study determined that leaching has little or no effect beyond boiling, and suggests that this step can be skipped. Of course, people under a doctor's care should check with their healthcare provider before making any such changes to their diet.
Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH, 43210-1044, or firstname.lastname@example.org.
Editor: This column was reviewed by Julie Shertzer, registered dietitian and program specialist for Ohio State University Extension in the Department of Human Nutrition, in the College of Education and Human Ecology.