The kidneys and their function

Want to know more about kidney function and chronic kidney disease? Whether you're concerned about your own health, somebody else's or for another reason, I answer some of the most common questions relating to kidney health. 


What is chronic kidney disease?

Kidney disease simply means that the kidneys have become damaged and unable to carry out their functions to a greater or lesser degree. 

Chronic kidney disease (CKD) refers to a gradual decline in function, which can progress over months or even years and is graded from stage 1, a very mild disease, to stage 5 when the need for treatment such as dialysis or a transplant is required. 

However, there is no need to panic if your kidney function has started to decline. Only a very small percentage of people with CKD go on to reach stage 5 and there may be things you can do to slow the process down.

What do our kidneys do?

What immediately springs to mind when you think about the functions of the kidney? I’m guessing that the production of urine is high on that list. In fact, the kidney is involved in a vast array of essential functions, in addition to getting rid of the additional fluids that we drink. Our urine takes with it compounds such as excess water-soluble vitamins and minerals, and the waste products that result from our body just doing its thing and renewing its cells regularly. 

Without our kidneys, we wouldn’t be able to manage our blood pressure or produce red blood cells. Without them, our bodies wouldn’t be able to use the vitamin D we consume and/or get from the sun, and our blood would eventually become too acidic. An impressive list of skills, I’d say.

Can I manage CKD with nutrition and lifestyle?

There are two aspects to this topic. 

The first is the role of nutrition in preventing further kidney damage. And the second involves potential changes to our diet to address the side effects of our kidneys’ reduced function.

So, how can we protect our kidney function if it starts to wane? 

Well, it depends on what is causing the kidneys to lose their function. If it is due to high blood pressure or diabetes, then adapting our diet and lifestyle to manage these conditions would be beneficial. That said, no matter the cause, we are likely to benefit from a healthy balanced diet and active lifestyle. 

Moving our bodies keeps the blood pumping around our organs, including the kidneys. A good blood supply gives the kidneys the best chance of working at their optimum level. Making sure we stay well-hydrated (unless advised otherwise) will ensure there is plenty of lovely blood to go around.

At an advanced stage of CKD, the kidneys become less effective at ridding the body of the compounds mentioned previously. This may mean that high levels of fluid or minerals, such as potassium and phosphate, are retained in the body. This can have negative effects on our health, hence dietary restriction of fluid or foods high in these minerals might be advised. 

Is it true that too much protein can do harm and worsen symptoms?

The simple answer is ‘yes, possibly’ and it does depend on what disease stage you are at. The waste produced after eating protein is excreted via our kidneys. If the kidneys are already damaged to some degree, a high intake of protein might put too much pressure on them, causing further damage. This doesn’t mean excessive restriction is necessarily required, however.

There is some evidence that reducing animal protein in favour of plant-based proteins may be a kidney-friendly approach, especially if you have diabetes. Do speak to a renal professional (preferably a dietitian) for guidance on the best approach for you. 

And, yes, if kidney disease results in an excessive build-up of protein waste products in our blood, we may feel unwell and nauseous. However, this would only occur at the end stage (stage 5) of kidney disease and it would be evident from your blood results. This is usually a sign that it is time for treatment.

What types of food should I be eating?

There are no ‘magic’ foods or diets that will miraculously protect or repair your kidneys and, at an earlier stage of CKD, if your diet is already balanced and varied, no changes may be necessary. 

Do I need to cut out salt?

No, not entirely. However, adopting a low-added salt diet would be wise, especially if blood pressure needs managing.

As a population, we obtain most of our salt from highly processed foods (e.g. salty snacks, fast food). So, the more you cook from fresh, the more control you have over how much salt you eat. Can’t face an egg without a sprinkle of salt? That’s no problem if, for the most part, you avoid adding it too liberally. 

A word of warning if you need to restrict potassium in your diet: some alternatives to salt (sodium chloride) are made from potassium chloride instead, so do check the labels. 

Can I restore my kidney function?

CKD refers to permanent damage to the kidney so, no, you can’t restore it. However, your function may drop only temporarily due to an infection, surgery or dehydration. In these cases, your function may recover to its previous level, depending on the seriousness of the cause.

How can a dietitian help me?

A dietitian can help you understand why dietary changes might be appropriate and give you the resources to make informed decisions about what you eat. They’ll take all the issues we’ve discussed above into account, such as diabetes and high blood pressure. We’re also pretty clued up on kidney-related medications and how medications and dietary changes can work together.

What would sessions look like?

An initial session would usually last an hour and you may well be asked to provide some medical history and a list of any medications. Many dietitians also ask you to keep a food diary for a few days beforehand, to understand what your diet looks like and to save time during the appointment. 

We like to follow up with our clients to check on their progress. Often, we jointly decide that further sessions would be useful, for example, to work on diabetes control or simply to support you in making and sustaining changes.

If you'd like to work with me, please visit my profile to enquire. You can also browse the profiles of other professionals listed on Nutritionist Resource.

The views expressed in this article are those of the author. All articles published on Nutritionist Resource are reviewed by our editorial team.

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Hassocks, West Sussex, BN6
Written by Annabel Alder, BSc Hons Nutrition & Dietetics | HCPC Reg. Dietitian
Hassocks, West Sussex, BN6

Would you like to feel better informed and supported with your chronic kidney disease? With 14 years' clinical experience, I am here to do just that and to put the joy back into eating.

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