Potato myths - how do I get the potassium out of them?
What is potassium and what properties does it have?
Potassium is an important building material in your body and regulates for example, the fluid content in a cell. But it is also responsible for the transmission of impulses in your nerves, so for the communication within your body. Almost all foods contain potassium, some more and some less. Plant-based foods in particular can contain quite a lot of potassium. Likewise, you may have heard that potassium is water soluble. This means that potassium escapes into the cooking water, when you boil something.
Why are potassium and kidney failure not good friends?
As you probably already know, the kidneys normally regulate the potassium in your body. If they can no longer do this, you need to be especially careful about your diet to avoid having too much potassium in your body. This may seem a bit strange, because many normally "healthy" foods contain a lot of potassium. However, it is incredibly important that you look at the potassium concentration in food.
How much potassium do potatoes contain?
Potatoes are real potassium bombs. That's probably one of the first things you'll hear about potassium and dialysis. But how much do they really contain? To give you concrete numbers, 250 grams of buttered potatoes already contain about 1,100 mg of potassium. Many dialysis patients are often recommended a daily guideline of between 1,500 and 2,500 mg. So that means that one serving of these can quickly fill well over half of the daily potassium budget in your diet. So it's true, potatoes contain a lot of potassium.
Are there potato varieties that are low in potassium?
Of course, there are potato varieties that are higher in potassium and potato varieties that are lower in potassium. The potassium content can vary by up to 50% between varieties. However, on the one hand it is often difficult to find information on this. On the other hand, it does not really change the fact that potatoes are extremely high in potassium across the board.
Is it true that I can put potatoes in water overnight?
For years, people with kidney disease were advised to simply put potatoes in water overnight for removing the potassium. This method is also sometimes recommended for other vegetables. While this method does remove some of the potassium, it unfortunately is not really as effective as you may hope. Regardless, for doing it correctly, it is important to peel the potatoes, cut them into slices, pour boiling water over them and then soak them. To soak the potatoes, it's best to just let them sit in the hot water at room temperature (not in the fridge) for a few hours or overnight. This will remove at least some of the potassium in the potato. When cooking the potatoes the next day, be sure to replace the water before starting to cook. By the way, it is also recommended to use significantly more water than potatoes (at least 4-5x as much water as potatoes)
Can I wash potassium out of potatoes?
You probably already guessed it - washing potatoes is unfortunately not effective. The potassium is in the potato itself, not just in the skin. If someone tells you that, then unfortunately that person just hasn't done their research well.
How much potassium is lost during normal cooking of potatoes?
Of course, it depends a bit on potato varieties. However, by rule of thumb, we can say that normal cooking of potatoes can remove about half of the potassium. However, this is not necessarily meaningful, because noone eats a raw potato? It is very important that you do not continue to use the cooking water, since it contains the potassium that you have removed.
Does more potassium escape when I cut potatoes into small pieces?
Yes, when you cut potatoes into pieces, more potassium escapes because of the increase in surface area. In other words, it means that water and potassium touch each other in more places, and thus more potassium can escape during cooking. So it makes sense to cut potatoes into chunks before cooking. It is also recommended to peel the potatoes before cooking.
Potatoes in the oven, steamed & fried - how much potassium is in them?
Unfortunately, you won't really be successful with these methods. As explained at the beginning, potassium is water soluble. Since the potatoes don't come into direct contact with water when applying these cooking methods, only a fraction of the potassium escapes. Processed foods like fries or mashed potatoes don't really contain less potassium either.
What about double cooking potatoes?
A very effective way to get much of the potassium out of potatoes is to double boil them. The best way to do this is to use as large a pot as possible with an extra lot of water. As just mentioned, you should pour away the cooking water of both times that you cook it. Do not use it again, because it contains a lot of the potassium that you have extracted. Unfortunately, however, it's also no secret that a lot of the flavour and texture of a potato is lost in the process.
So what does this mean for everyday life as a dialysis patient?
To avoid eating a tasteless diet, you can actually get into the habit of the following tactics:
The most effective method is to think about what alternatives to potatoes taste good to you in certain meals. In many dishes and recipes, pasta, rice, or other grains such as couscous work well instead.
You can also consider simply reducing the amount of potatoes in a mixed portion. If you don't want to miss out on the taste of potatoes, you could also consider simply reducing the amount of potatoes in a meal as a first step.
When you do eat potatoes, cook them in small pieces and replace the cooking water after cooking. If double cooking works for you, even better.
Try seasoning your food with tasty spices. These may also be high in potassium, but the amounts of seasoning are relatively small.
A practical example:
So, for example, if you're making a vegetable soup and you really want to put potatoes in it, here are five things you can do: (1) soak potatoes over night in hot water (2) cut potatoes into small pieces, (3) boil them separately, and (4) add them to the soup without the cooking water. Lastly, don't forget to (4) reduce the total amount of potato in the soup.
Potatoes are potassium bombs - but potassium is water-soluble, so some of it can be selectively reduced during cooking
If you soak potatoes overnight, you should peel them, cut them into pieces, pour boiling water over them, and then let them sit at room temperature overnight
Even more effective is the extended boiling of potatoes that were cut into small pieces (pour away the cooking water!)
DaVita Nutrition Tips: „Tipps für eine nierenfreundliche Ernährung", accessed on 15.12.2021
The Effects of Boiling and Leaching on the Content of Potassium and Other Minerals in Potatoes; P.C. Bethke, S.H. Jansky (2008), Journal of Food Science
Cooking Legumes: A Way for Their Inclusion in the Renal Patient Diet; M. Martinez-Pineda, C. Ygüe-Ruizu, A. Caverni-Munoz, A. Vercet-Tormo (2019), Journal of Renal Nutrition
Changes in Potassium Content of Different Potato Varieties After Cooking; J. D. Burrowes, N. J. Ramer (2008), Journal of Renal Nutrition