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Potassium danger: Do you have too much of it in your diet?

Potassium is a hugely beneficial mineral for the body, unless you already have a lot of it.

QUESTION: My doctor has advised me that, at the age of 83, I have high blood pressure and high potassium. Other than telling me to not eat bananas, he mentioned no other foods. Which high-potassium foods should I avoid? Online food lists are contradictory and include many everyday healthy foods.

ANSWER: You’re quite right: many everyday potassium-rich foods are beneficial to our health. The mineral plays a major role in maintaining fluid and electrolyte balance and, consequently, the integrity of our cells. It also helps with nerve impulse transmission and muscle contraction.

Potassium-rich foods assist in lowering blood pressure by balancing out the negative effects of salt. The more potassium you eat, the more sodium you’ll lose through urination. It also helps to ease tension in blood-vessel walls, further lowering blood pressure.

The heart- and well-being-boosting mineral is found in the cells of all wholefoods such as meat, milk, fruits, vegetables, grains and legumes.

However, as you’ve discovered, that makes life difficult when you’ve got too much potassium in your body. Symptoms of excess potassium can include tiredness, nausea and numbness – severe cases can result in heart failure – which is why your GP would recommend limiting potassium intake.

Without knowing your full medical history, it’s impossible to understand your specific situation. However, kidney function does decline with age in almost everyone. And, given that excretion of potassium is a key function of the kidneys, it’s possible that declining kidney function is the cause of your raised levels.

Our kidneys normally filter half a cup of blood every minute, removing waste and extra water to make urine. They remove acid produced by your cells and maintain a healthy balance of water, salts and minerals such as sodium, calcium, phosphorus and potassium in your blood. They also make hormones that help to control blood pressure, make red blood cells and keep bones strong.

Finding a good balance for you simply means limiting or avoiding certain foods. For example, you can still eat two servings of fruit a day, but try to limit high-potassium fruits such as bananas, apricots, mangoes, grapes (in large quantities), kiwifruit, dried fruit and fruit juices.

Similarly, high-potassium vegetables to avoid or reduce include potatoes, kūmara, pumpkins, tomatoes, avocados and cauliflower.

Other high-potassium foods include bran-based cereals, breads with bran or large amounts of wholegrains, dairy products such as milk, yogurt, custard and ice cream as well as nuts, large servings of meat, chicken and fish and strong coffee.

It’s almost impossible and definitely unhealthy to have a potassium-free diet. Instead, it’s a matter of limiting the foods just mentioned. You would also benefit from consulting a dietitian about how to manage your dietary modifications and potassium levels.

Practical tips to manage high potassium levels:

  • Limit fruit to two servings a day, choosing low-potassium options such as apples, strawberries, mandarins, passionfruit, pears or a small slice of watermelon.
  • Limit fruit juice to no more than 150ml a day.
  • Drain liquid from tinned fruit.
  • Reduce serving sizes of starchy vegetables such as potatoes, kūmara and pumpkins to half a cup a day.
  • Choose low-potassium options such as pasta, white bread, rice, carrots, beans, corn, asparagus and zucchini.
  • Peel and boil vegetables to leach some of their potassium – don’t consume the cooking water, and avoid vegetable soup.
  • Avoid large servings of tomatoes including in pastes, purées and soups.
  • Avoid cereals high in bran.
  • Don’t use salt substitutes.
  • Avoid liquorice, chocolate, potato chips and strong coffee.
  • Limit dairy products to 200g of yogurt or 300ml of milk a day (but not both).

Source: Royal Australian College of General Practitioners. 

This article was first published in the December 7, 2019 issue of the New Zealand Listener.