Kidney Disease Diet: Lower Acid Load, Watch Potassium

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Why acid load matters in kidney disease

Healthy kidneys easily excrete the acid from your diet. As kidney function declines, this gets harder. From about stage 3 to 4, many patients see their blood bicarbonate drop, and metabolic acidosis develops. It is more than a lab value: it promotes muscle loss, strains the bones and is linked to a faster loss of kidney function.

In observational studies, people with a high dietary acid load, measured as PRAL or as estimated net acid load, had a higher risk that their kidney disease would progress. In intervention studies by the research group of Nimrit Goraya and Donald Wesson, alkalizing fruit and vegetables improved blood values in patients with stage 3 and 4 disease and early acidosis about as well as sodium bicarbonate tablets. Patients with high potassium were excluded, and potassium was monitored closely. This limitation is the heart of the topic.

To learn how to estimate the acid load of individual foods, read the article PRAL value.

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The conflict: alkaline often means high in potassium

Potassium is the most important alkaline nutrient in the PRAL. That is why spinach, bananas, potatoes, avocado and dried fruit are so alkaline, and these are exactly the foods on the lists to avoid when potassium is high. High potassium in the blood (hyperkalemia) can trigger heart rhythm problems. The risk rises in advanced stages and with medications such as ACE inhibitors, ARBs (angiotensin receptor blockers) or potassium-sparing diuretics.

But there are alkaline foods that are low in potassium:

Nutrient values and PRAL: Basentracker food database (German Nutrient Database, Bundeslebensmittelschlüssel 4.0, and other sources, see Sources).

You can also reduce potassium: cut potatoes and vegetables into small pieces, soak them for a few hours, boil them in plenty of water and pour off the cooking water. This lowers the potassium content by one third to one half. The PRAL drops along with it, so the food becomes less alkaline, but it usually stays in the negative range.

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Protein: less, not more

Protein is the strongest acid former in your diet, and it puts extra strain on the kidneys through the filtration load. The international KDIGO guideline recommends that adults with chronic kidney disease from stage 3 who are not on dialysis eat about 0.8 g of protein per kilogram of body weight per day, and it advises against a very high-protein diet. For 70 kg, that is about 56 g.

Plant protein sources have two advantages here: less acid load per gram of protein, and phosphorus that is absorbed less well than from animal sources. Legumes, however, are high in potassium, so here too your lab values decide. Different rules apply on dialysis, where more protein is usually recommended.

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Phosphate: a double win

Phosphorus raises the PRAL, and in kidney disease it also strains the blood vessels and bones. Phosphate additives have the strongest effect because they are absorbed almost completely: processed cheese, cooked sausages, cooked ham, cola, baking mixes and ready meals. On the ingredient list they appear as phosphate, diphosphate, polyphosphate or E 338 to E 341 and E 450 to E 452. If you avoid these products, you lower phosphate and acid load at the same time.

For an overview, see the table low-phosphorus foods with a potassium column.

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What this means for everyday life

1. Know your lab values. Potassium, phosphate and bicarbonate in your blood determine how much leeway you have.
2. Alkaline and low in potassium. Make apples, berries, grapes, cucumber, cauliflower, bell peppers, zucchini and lettuce your foundation.
3. Moderate protein. Smaller portions of meat, fish and cheese, with part of your protein from plant sources if your potassium allows it.
4. Avoid phosphate additives. Cook fresh instead of buying ready-made products, and cut out processed cheese and cooked sausages.
5. Go easy on salt. Less salt protects your blood pressure and your kidneys.