Foods, Kidney Disease, Potassium and Oxalates

Kidney team guidance comes first

Many foods praised elsewhere on this site, such as beans, leafy greens, nuts, bananas and tomatoes, are rich in potassium or oxalate. For most people that is not a problem. For people with kidney disease or a history of kidney stones, the right limits depend on blood tests and the kidney type, and they are set by the kidney team and a dietitian. This page explains what the sources say; it gives no personal limits. Do not stop a prescribed medicine, and do not change your diet on your own because of a web page.

Chronic kidney disease: what the NIDDK says

The NIDDK (US National Institute of Diabetes and Digestive and Kidney Diseases) says that when kidneys cannot filter blood properly, what you eat and drink can help keep salts and minerals in balance, and that needs change as the disease advances [1]. It says there is no single meal plan for everyone with chronic kidney disease (CKD), and that in early stages there may be few limits [1].

Potassium in everyday foods

MedlinePlus says vegetables and fruit are the richest sources of potassium, and names beans, lentils, tomatoes, potatoes, sweet potatoes, soy, winter squash, citrus fruits, cantaloupe, bananas, kiwi, prunes and apricots, plus milk, yogurt and nuts [2]. It says people with kidney problems, especially those on dialysis, should not eat too many potassium-rich foods, and that the provider will recommend a restricted diet if needed [2]. The same page names ACE inhibitors, angiotensin receptor blockers and potassium-sparing water pills as common causes of high blood potassium, along with poor kidney function [2].

The NIDDK says that if potassium is high, a health professional may advise limiting serving sizes of potassium-containing foods, using herbs and spices instead of salt substitutes (which can be high in potassium), and limiting foods with potassium chloride on the label [1]. Potassium is also covered in Potassium: Roles, Food Sources and Cautions and Foods High in Potassium. Because potassium-rich foods are also linked in the library to blood pressure, see Foods for Blood Pressure with this caution in mind. Contact the kidney team about any change, and about supplements and minerals; see Minerals, Supplements and Kidney Disease.

Oxalates and kidney stones

The NIDDK says drinking enough liquid, mainly water, is the most important thing for preventing kidney stones, unless you have kidney failure [3]. For people who have had calcium oxalate stones, it says they may want to avoid foods that raise oxalate in urine, and lists nuts and nut products, peanuts, rhubarb, spinach and wheat bran [3]. It tells them to talk with a health care professional about other food sources and how much oxalate they should eat [3].

Other points from the same source:

• Ask your health care professional which type of kidney stone you had, because food advice differs by type [3].
• Sodium raises the chance of stones, and animal protein may increase it too [3].
• Calcium from food is not the cause of calcium stones; in the right amounts it can block other substances that may cause stones [3].
• Studies have shown that the DASH diet can reduce the risk of kidney stones [3].
• Beans, dried peas and lentils are described as high in protein and low in oxalate [3].

The oxalate content of most other functional foods, and whether cooking or soaking changes it, was not found in the sources read for this page. Proper evidence was not found for general oxalate limits for people who have never had a stone. For vitamin C supplements and stones, see High-Dose Vitamin C.