Are Potatoes Acidic or Alkaline? PRAL Values and Chart

The short answer

Potatoes are alkaline-forming. On the PRAL scale, which estimates what a food leaves for your kidneys to clear after digestion, a raw potato with its skin scores about -6.6 per 100 grams and a baked potato with skin scores about -8.3. A negative number means base-forming, which is what food lists mean when they call something alkaline.

If you have read that potatoes are acidic, that usually comes from a different measurement. The flesh of a raw potato has a pH a little below neutral, roughly 5.4 to 5.9 on the FDA's table of approximate food pH values. That number describes the potato on the cutting board. PRAL describes the potato after you have eaten it, and that is the measure alkaline food lists are built on.

Neither number tells you anything about your blood. The body keeps blood pH in a narrow range, around 7.35 to 7.45, whatever you eat. Food shows up in urine, which is what Remer and Manz measured when they designed PRAL. On this site, alkaline is a recipe label for plant-forward cooking, not a promise about body chemistry.

How the potato number is worked out

PRAL uses five nutrients per 100 grams. Protein and phosphorus push the score up. Potassium, magnesium and calcium pull it down. The Remer and Manz formula is: 0.49 x protein (g) + 0.037 x phosphorus (mg) - 0.021 x potassium (mg) - 0.026 x magnesium (mg) - 0.013 x calcium (mg).

USDA FoodData Central lists a raw potato, flesh and skin, at about 2.1 grams of protein, 57 milligrams of phosphorus, 425 milligrams of potassium, 23 milligrams of magnesium and 12 milligrams of calcium per 100 grams. Run those through the formula and you get about -6.6. Potassium does almost all of the work. A potato is low in protein and rich in potassium, which is exactly the combination that lands a food below zero.

A baked potato with skin scores lower, about -8.3, because baking drives off water. The same minerals now sit in fewer grams, so each 100-gram portion carries more potassium. Remer and Manz's original 1995 table listed potatoes at about -4.0. Their figure used older nutrient data, so it does not match ours to the decimal, but it points the same way.

White, red, sweet, fries and chips

White, yellow and red potatoes all share the same basic profile: mostly water and starch, a little protein, and a lot of potassium. Expect all of them to land below zero. The skin holds a good share of the minerals, so eating potatoes skin-on keeps the number at its lowest.

Sweet potatoes are a different plant, but they behave the same way on this scale. A baked sweet potato in its skin comes to about -8.2 using USDA values, almost identical to a baked white potato.

Fries and chips are still potatoes, and frying does not add protein or phosphorus, so they stay on the alkaline side of the chart. Frying concentrates the minerals by removing water, which can push the score lower per 100 grams. What changes is everything PRAL ignores: oil, salt and portion size. A low PRAL score does not make fries an everyday food, and nothing on this page should be read that way.

Where potatoes sit among 30 everyday foods

Our full alkaline foods list and PRAL chart ranks 30 foods we cook with, calculated the same way from USDA data. Potatoes sit in the middle of the vegetable group. Here is the short version, in mEq per 100 grams:

More alkaline than potatoes: raisins -14.5, spinach -11.8, sweet potato baked -8.2, avocado -8.2, kale -8.0, banana -6.9. Close to raw potatoes: potato raw -6.6, carrots -5.7, cauliflower -4.4, tomato -4.1, broccoli -4.0. Near neutral: tofu +0.1, plain whole-milk yogurt +0.1, lentils cooked +2.1, brown rice cooked +2.3. Acid-forming: egg +9.6, salmon cooked +11.1, chicken breast roasted +17.3, cheddar +17.3.

For the other end of the scale, our acidic foods list covers 35 cheeses, meats, fish, nuts, grains and drinks.

Cooking with potatoes on an alkaline-leaning plate

PRAL adds up across a meal, which is why potatoes are so useful. A 200-gram baked potato, skin on, brings about -16.6 to the plate. That is enough to balance a modest portion of chicken or cheese, which is the practical point of the chart: build around vegetables and potatoes and let richer foods be part of the meal rather than all of it.

Easy ways to do that: roast potato wedges on the same tray as carrots and broccoli, following our batch roasting guide. Add cubed potatoes to a pot of vegetable soup, as in our note on soup as a vegetable strategy. Top a baked potato with a spoonful of herb sauce from our herb sauces guide instead of a pile of cheese.

Related questions

Is garlic acidic or alkaline? Mildly acidic in pH and slightly alkaline-forming by PRAL. Our garlic guide works through the numbers.

Are herbal teas alkaline? Most plain teas are close to zero. See our alkaline-friendly teas guide.

Do potatoes have too much potassium for some people? They can. People with kidney disease or anyone told to limit potassium should follow their own clinician's advice. Many foods at the alkaline end of the chart are high in potassium for the same reason they score low.

Medical disclaimer

This article is general food education for a recipe audience. It does not provide medical advice, diagnosis, or treatment, and it does not claim that potatoes or any other food change blood pH or prevent, treat, or cure any disease. Alkaline, on this site, is a lifestyle and recipe label for food. Please also read the full disclaimer.

Sources

Remer T, Manz F. Potential renal acid load of foods and its influence on urine pH. Journal of the American Dietetic Association. 1995;95(7):791-797. https://pubmed.ncbi.nlm.nih.gov/7797810/

U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, SR Legacy: Potatoes, flesh and skin, raw; Potatoes, baked, flesh and skin; Sweet potato, cooked, baked in skin. https://fdc.nal.usda.gov/

U.S. Food and Drug Administration. Approximate pH of Foods and Food Products.

Schwalfenberg GK. The alkaline diet: is there evidence that an alkaline pH diet benefits health? Journal of Environmental and Public Health. 2012. https://pmc.ncbi.nlm.nih.gov/articles/PMC3195546/