Lowering Potassium in Potatoes

Written by DaVita renal dietitian, Sara Colman, RD, CSR, CDE

Potassium  is a mineral that controls nerve and muscle function. One very important muscle — the heart — beats at a normal rhythm because of potassium. In addition, potassium is necessary for maintaining fluid and electrolyte balance and pH level. Healthy kidneys help keep potassium at a normal level. Potassium levels that are too high or too low can be dangerous.

Potassium comes from the foods we eat, and healthy kidneys remove excess potassium in the urine to help maintain normal levels in the blood. However, because people with chronic kidney disease (CKD) or people on kidney dialysis  do not have healthy kidneys, potassium may build up in their bodies. For this reason, people with CKD and those on hemodialysis may have to limit foods high in potassium or find ways to remove potassium from the foods they eat.

Why is too much potassium harmful to people with kidney disease?

High potassium in the blood is called hyperkalemia. This can occur in people with advanced stages of chronic kidney disease (CKD).

Some of the effects of high potassium (hyperkalemia) are:

  • nausea
  • weakness
  • numbness or tingling
  • slow pulse
  • irregular heartbeat
  • heart failure
  • sudden death

For people with stage 5 CKD (also known as end stage renal disease or ESRD), dialysis is necessary to help regulate potassium. Dialysis is very effective at removing excess potassium from the blood. For those who do peritoneal dialysis or daily home hemodialysis, high potassium is rarely a problem. However, in patients who get intermittent hemodialysis three times each week, potassium levels may rise in between treatments. Because of this, high potassium foods must be limited so potassium levels do not get too high before the next treatment.

High potassium (hyperkalemia) is likely to occur when dialysis treatments are skipped or shortened or when large amounts of foods high in potassium content are consumed between treatments. This allows potassium to build up to dangerous levels in the blood, which can lead to irregular heartbeats and even cause the heart to stop beating.

Potassium and potatoes

Certain high-potassium foods can be soaked in water to reduce their potassium content for people on the kidney diet. Potatoes are one of these foods, and recent research has revealed new ways of cooking potatoes to remove the maximum amount of potassium.

For years, renal dietitians have instructed kidney patients on low potassium diets to cut up and leach or soak potatoes to reduce the potassium load. That’s because one small potato (1-3/4" to 2-1/4" diameter) contains over 700 milligrams of potassium.

A review of the research on treatments to remove potassium reveals there are three important factors to consider when cooking potatoes:

  • dicing, slicing or grating potatoes into smaller pieces helps to maximize exposure of the potato surface to water
  • the temperature of the water used to either soak or boil the potatoes makes a difference
  • a large volume of water to potatoes is required
  • boiling unsoaked potatoes twice with a change of water between boiling periods lowers potassium to amounts comparable to potatoes soaked at room temperature or higher then boiled once

What research has been done on removing potassium from potatoes?

During early research in 1969, potatoes were sliced into 1/8th-inch slices or diced into small dice-size cubes and soaked in heated water (122 to 140° F) for two hours. The water volume was 10 times more water than potatoes. Next, the potatoes were rinsed and boiled in five times more water for five minutes. This method of soaking and then boiling the potatoes reduced potassium from 400 milligrams per every 100 grams (equal to 2/3 cup) of potatoes to 211 milligrams for cubes and 90 milligrams for thinly sliced potatoes.

A study in 1970 analyzed dehydrated and raw potato slices repeating the above techniques. This new study demonstrated a reduction in potassium to 86 milligrams by leaching thin sliced potatoes in room temperature water instead of heated water for 30 minutes. The results confirmed that maximum surface exposure with a large amount of water at room temperature or higher effectively removed potassium.

Another study in 1990 analyzed cubed, grated and French-fry-cut potatoes soaked in the refrigerator in cold water (40° F) for four hours. Ten times the amount of water to potatoes was used. In this study, potassium in raw potatoes was reduced from 340 milligrams to 290 milligrams after four hours of leaching. For the grated potatoes soaked in the refrigerator, potassium was 150 milligrams after four hours. The French-fry-cut potatoes were 340 milligrams after four hours of soaking.

A 2008 study analyzed 1/2-inch cubed potato pieces (that’s very small) and grated potatoes soaked in the refrigerator for 20 hours at 42° F and then boiled. The results showed that boiling reduced the potassium just as effectively as soaking then boiling. The raw potato cubes that were not leached contained 400 milligrams of potassium. However, after boiling for 10 minutes in a large volume of water, the boiled cubes were reduced to 200 milligrams of potassium, and the boiled grated potatoes were reduced to 100 milligrams of potassium.

Yet another study in 2008 compared potato varieties and potassium removal without soaking. Instead 1/8" potato slices were boiled until tender. One batch was boiled once as with normal cooking (NC). The second batch was brought to a boil, drained, and then boiled until tender, called double cooking (DC). Results revealed that potassium removal was effective although the amount varies with potato variety. Idaho, red, purple, white and Russian fingerling potatoes had potassium content ranging from 162-194 mg/100 g after double cooking. Yukon gold potatoes were higher, 235 mg/100 g.

These studies are reflected in the chart below: 

Study year/
Researchers

Potato
cut

Water temp

Soak time

Boil time

Potassium before soaking 

Potassium after soaking

1969
Tsaltas

1/8" slices

heated to 122-140° F

2 hours

5-10 minutes

400 mg 

90 mg

1969
Tsaltas

dice-size cubes

heated to 122-140° F

2 hours

5-10 minutes

400mg

211 mg

1970 Louis

dehydrated slices

room temp

30 minutes

5-10 minutes

400mg

86 mg

1970 Louis

1/8" slices

room temp

30 minutes

5-10 minutes

400 mg

86 mg

1990 McVeigh

1" cubes

40° F

4 hours

none

340 mg

290 mg

1990 McVeigh

grated

40° F

4 hours

none

380 mg

150 mg

2008
Bethke/ Jansky

1/2" cubes

42° F

20 hours

10 minutes

400 mg

200 mg

2008
Bethke/
Jansky

grated

42° F

20 hours

10 minutes

400 mg

100 mg

2008 Burrowes

1/8" slices

212° F

0 minutes

5-10  minutes double cooked

295-448 mg*

162-235 mg*

*Potassium varied with potato variety. Idaho, red, purple, white and Russian fingerling potatoes potassium

What’s the best way to reduce potassium in potatoes?

For the most effective potassium removal, potatoes must be cut into small pieces, sliced thin or grated. If boiled at least 10 minutes in a large pot of water, potassium is reduced by at least half the original amount. These potatoes will still contain 100 to 200 milligrams of potassium in a 1/2 cup serving so people on a low-potassium diet are encouraged to pay attention to portion control.

If boiling is not the planned cooking method, potassium may still be reduced by slicing or cutting potatoes into small pieces or grating them and soaking them in a large amount of water at room temperature or warmer for greater potassium removal.

The least effective method of removing potassium is to soak potatoes in the refrigerator, then prepare without boiling first.

What about other forms of potatoes?

Canned potatoes go through a natural leaching process due to soaking in the canned water. A 1/2 cup serving of drained canned potatoes that is one inch in diameter contains 206 milligrams of potassium.

Instant potatoes are highly processed and do lose some potassium during processing. A 1/2 cup serving of prepared potato granules or flakes contains 150 to 220 milligrams of potassium.

Hash browns, either frozen or home prepared, contain 340 to 450 milligrams of potassium in a 1/2 cup portion. Grated potatoes that are soaked or boiled according to the researchers’ methods and then fried contain between 100 to 150 milligrams of potassium in a 1/2-cup portion.

It’s easy to get too much potassium from potatoes

One average-sized, whole, baked potato (2-1/3"x 4-3/4" or about 1-1/3 cups, if measured) contains 926 milligrams of potassium with the skin or 610 milligrams of potassium without the skin. If you are on a low-potassium diet, this is a considerable amount for one serving.

Potato chips are another source of too much potassium. A comparison of 16 different varieties and brands reveals a range of 265 to 495 milligrams of potassium for one cup of chips or a one-ounce bag.

People on low-potassium renal diets should also beware of French fries. A small order of fries from five major fast food chains ranges from 470 to 510 milligrams of potassium. That’s about 20 milligrams for each French fry. A super-sized order has 1,210 milligrams potassium — more than half the daily allowance for a low-potassium diet.

What about other vegetables?

While leaching and soaking work for potatoes, it’s not recommended that you soak or boil all vegetables in water because water soluble vitamins including B vitamins and vitamin C are lost in the water. Also, all vegetables are different and do not lose the same amount of potassium when leached or boiled.

A 2006 study on a variety of tuberous root vegetables (batata, cocomalanga, dasheen, eddo, black yam, white yam, yellow yam, yampi, malanga, red yautia white yautia and yucca) that were consumed as a staple by different ethnic groups determined that leaching alone did not remove enough potassium in these vegetables. By boiling, rinsing and boiling again, dasheen, yams and yampi were reduced below 200 milligrams of potassium per 100 grams. Batata, white yautia and yuca were reduced to below 300 milligrams after double boiling. Cocomalanga, eddo, malanga and red yautia remained over 300 milligrams after boiling.

Summary

The next time you want potatoes on a low-potassium kidney diet, remember to reduce potassium in fresh potatoes by cutting into small pieces, slicing thin or grating; then boil or soak in water. If leaching, use tap water or warmer water. Leaching is not necessary if potatoes are boiled to prepare. Use a large pot of water when soaking or boiling. Finally, remember portion control.


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