By Laura Kyte, Renal Dietitian, Royal Devon and Exeter Hospital

If you have reduced kidney function the removal of excess fluid can become problematic. Your doctor or nurse may prescribe medication to try and increase the amount of urine you pass and they may also ask you to restrict your fluid intake.

It is much easier to cope with a fluid restriction if you are also aware of the amount of salt in your diet. Salt can make you thirsty, raise your blood pressure and can lead to fluid retention. A daily intake of 6 grams or 1 teaspoon of salt (or less), as recommended by the UK Food Standards Agency, should help to control thirst.

Where possible we try to encourage people to cook from fresh rather than using processed foods or ‘ready meals’ in order to reduce their salt intake. For example, a jar of shop-bought tomato pasta sauce contains 0.7g salt per 100g compared to just 0.02g per 100g of homemade sauce using tinned tomatoes, onion, garlic and herbs. A slice of ham can contain 0.5g salt compared to 0.05g in the same portion of roasted chicken. A range of herbs and spices can be used to give flavour to food, but salt substitutes such as Losalt are not recommended as they are high in potassium, which is not suitable for many kidney patients. Salt substitutes also do not address the dependence on salty-tasting food which, can be better achieved by gradually cutting back on the amount of added salt.

If you are using processed foods, reading the label can help to identify foods that are high in salt, and allow you to compare products in order to choose the lower-salt option. In general, a product with more than 1.5g of salt per 100g is HIGH in salt and one with 0.3g of salt or less per 100g is LOW in salt. The British Heart Foundation have a useful leaflet, which includes a food labelling card that can be kept in a wallet and taken shopping for reference.

People tend to drink both from thirst but also out of habit. Some practical suggestions for controlling your fluid intake include: using a tea cup rather than a mug (can save 100ml per drink!), measuring your cup volume to work out how many you can have in a day, and also try swallowing your tablets with food if you possibly can.

If you have a dry mouth, try sucking an ice cube, chewing gum or a sugar free sweet, as all these can stimulate saliva production. Even swilling your mouth with some mouthwash can help ease a thirst. And another useful tip - plastic ice cubes can cool your drink without contributing extra fluid in the hot weather.

We know it’s not easy to monitor every last drop of liquid you take in but if you try to make small adjustments to your intake you WILL start to feel better, quicker. Remember, though, it is not just drinks which need to be considered when you are trying to restrict the amount of liquid you take in. Milk on cereal, jelly, yogurts, gravy, soup and ice cream all have a high water content and really do need to be included.

Your personal fluid restriction can vary depending on the amount of exercise you take, the temperature and the amount of urine you pass. If you are concerned about your fluid intake just ask your kidney doctor, nurse or dietitian.

Article was first published in Kidney Matters Summer 2018, Issue 2 (PDF, 3mb)