This clinical trial aims to investigate and test the effect of an acid/base diet in chronic kidney disease (CKD) patients, CKD stage 4 and 5. The trial is guided by the hypothesis that an acid/base diet will reduce the degree of acidosis and simultaneously reduce the need for bicarbonate supplements.

Observational studies indicate that diets with a low "potential renal acid load (PRAL)" is associated with a lower serum-bicarbonate value. Therefore, we aim to investigate this association through an interventional study design.

Participants will be asked to follow a restricted diet with a low "PRAL" during a 6-week trial divided into three periods: two-week of free-living control, two-weeks of intervention, and a two-week free-living follow-up.

The PRAL calculation tool will be used to create a diet low in acid and to develop individualized diet plans for each patient. The diet will comply with Danish national guidelines on threshold for potassium and protein, due to the high risk of hyperkalemia in CKD patients. The patients will be asked to document their food and drink intake by taking pictures of their plates and cups before and after a meal, over a 24-hour period.

Inclusion Criteria:

• Chronic acidosis (plasma-bicarbonate under 22 mmol/l at multiple measures within the last 12 months).
• Diagnosed with non-dialysis needed chronic kidney disease in stage 4 and 5 (eGFR below 30 ml/min/1,73 m2)
• Of legal age and over 18 of years
• Understand danish and understand the written material
• Able to cooperate about the diet
• Able to take pictures with their phone or willing to learn

Exclusion Criteria:

• Vegan and vegetarian with very low intake of animal protein (below 25 g/day)
• Pregnant or breast feeding
• Patients with short bowel syndrome, bricker bladder, pancreatitis or any other known malabsorption problem
• Potassium above 5 mmol/l
• Ongoing infection

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