People with chronic kidney disease (CKD) are often concerned about eating tomatoes if they have been advised by their renal dietitian to follow a low potassium diet.

However, in the right amount and served with the right foods, tomatoes can still be enjoyed safely.

One of the main aims of the Kidney Kitchen is to give you as much variety as possible and that means including tomatoes in some of our recipes – but only when combined with low potassium ingredients. The overall potassium content of the Kidney Kitchen recipes has all been carefully analysed to ensure that those marked ‘low potassium’ are suitable for people with CKD who have been advised to follow a low potassium diet.

Including tomatoes in your diet safely if you are reducing your potassium levels

Finding the balance of low and high potassium foods can be worrying when you have kidney disease. That often means it is easier to simply avoid foods which are high in potassium. However, many high potassium foods can be included safely and will provide you with other essential nutrients as well as enhancing your enjoyment of food.

One of the most common questions we are asked as renal dietitians is whether people with CKD can eat fresh tomatoes and whether it is ok to use tomatoes in cooking.

If you wish to include high potassium foods such as tomatoes in your diet it is worth considering:

• How much of these foods you have (portion size)
• How often you have them (frequency)
• What form they’re in (tinned, pureed, juice, fresh)
• What you serve them with (accompaniments)

We recommend that you always follow any specific advice given by your renal dietitian.

Including tomatoes in a low potassium diet: portion size

Most people with CKD can safely eat one medium (80g) tomato daily (as a one of your 5 a day), perhaps served with a cooked breakfast, lunch or salad.

Canned tomatoes used in cooking are often divided into several portions for the finished meal. A quarter of a medium size can of chopped tomatoes provides roughly the same amount of potassium as one tomato (100g).

Including tomatoes in a low potassium diet: frequency

Many high potassium foods such as tomatoes can be eaten in small amounts, depending on your bloods results. You shouldn’t exceed more than one small portion per day (in other words, don’t include in more than one meal per day).

If you often experience high potassium levels you may want to limit this further (i.e. down to 1-3 times per week).

Including tomatoes in a low potassium diet: tomato juice and tomato puree

It is worth noting that tomato juice and tomato puree are often more concentrated than tomatoes or canned tomatoes. Tomato puree is therefore used in much smaller amounts than canned tomatoes in our Kidney Kitchen recipes. In addition to this we reduce or omit other vegetables in these recipes to allow for the higher potassium tomatoes.

In general we advise not to drink tomato juice if you follow a low potassium diet.

Be potassium aware

Being ‘potassium aware’ – knowing which other foods are high in potassium – can help you to ensure that you can have variety in your diet and help keep your potassium levels safe by not having too many ‘high’ foods on one day.

Serving a tomato-based meal with low potassium accompaniments will help to keep the meal’s total potassium content to a low level. Using bread, pasta or rice rather than potato is one way of doing this.

Many different things can affect your blood potassium level including your appetite, dialysis adequacy, medication, blood glucose levels and bowel function. We recommend you speak to your renal dietitian for individualised advice based on your blood results.

Overall, the more you know about the foods that you enjoy eating regularly, the more you are able to safely include a wider variety of foods.

This article was first published in Kidney Matters magazine, issue 13.