Are Potatoes Acidic or Alkaline?

The pH of a potato is around 5.4 to 5.9, making it a mildly acidic food. But if you're interested in eating an alkaline diet, the potato's potential renal acid load, or PRAL, is more important.

Before diving into the pH of a potato, here's a quick recap of acidity and alkalinity, as explained by Iowa State University Extension and Outreach. Both concepts are measure by the pH scale, which runs from zero (very acidic) to 14 (very alkaline or base).

A pH of 7 is defined as the neutral "tipping point," while a pH of less than 7 is considered acidic and a pH of greater than 7 is alkaline or base. The further you get from that neutral point of 7, the more acidic or alkaline the substance is.

As noted at Clemson University Cooperative Extension, the pH of a potato is approximately 5.4 to 5.9. Although the specific pH can vary — depending on growing conditions, processing methods and the potato variety in question — that places potatoes soundly on the "mildly acidic" side of the scale.

But as Traci Roberts, a registered dietitian with the University of California San Diego explains, it's not the pH of the food itself, but instead the potential acid load the food exerts on your kidneys, that matters when considering an acid or alkaline diet.

That's because your lungs and kidneys do most of the work of controlling the pH of your blood. As noted in a data analysis published in a 2012 issue of the ​Journal of Environmental and Public Health,​ other parts of your body necessarily exist at different pH levels — but your blood absolutely must have a mildly alkaline pH of approximately 7.4.

Which brings you back to the question of potential renal acid load — a better way to measure the acidifying or alkalizing effect of foods on your kidneys, and thus your body. As Roberts explains, that different way of quantifying acid load is why acidic citrus fruits are actually considered a high-alkaline food — the fruits' pH is acidic, but they have a low renal acid load on your body.

Although Roberts doesn't discuss potatoes directly, the ​Journal of Environmental and Public Health​ article does, noting that potatoes have a negative (low) renal acid load. So, within the context of an alkalizing diet, the potato is considered an alkaline food — despite the mildly acidic pH of the potato itself.

​Read more:​ Acid vs. Alkaline in the Body

Should you be steering your choice of potatoes — and other foods — strictly according to their alkalizing value? Not necessarily, says Roberts, warning that if you were to adopt a strict diet of 80 percent alkaline foods and 20 percent acidic foods, you'd be at increased risk of certain vitamin and protein deficiencies.

Roberts goes on to note that the top dietary guidelines have remained the same for more than 30 years. When in doubt, it always pays to consult the Department of Health and Human Services' Dietary Guidelines for Americans, which include time-tested recommendations such as:

• Eat a variety of vegetables from every subgroup.
• Eat plenty of fruit, especially whole fruits.
• Make at least half your grain consumption come from whole grains.
• Consume fat-free or low-fat dairy.
• Choose high-quality sources of lean protein.
• Limit your intake of saturated fat, added sugar and sodium.

These guidelines steer you toward a well-balanced diet free from potential nutritional deficiencies, while helping you avoid or limit the highly processed foods that tend to be high in calories but low in nutrition.

If you're considering an alkaline diet to better support your kidneys, take note: A balanced diet also avoids the type of low-carbohydrate, high-protein diet that the authors of the ​Journal of Environmental and Public Health​ article warn won't make much of a difference in your blood chemistry and pH, but can produce many changes in your urinary chemistry and increase your risk of kidney stones.

Ultimately, a registered dietitian can help you decide which foods are best for you. If you're dealing with kidney issues or other medical problems, your medical provider will have useful guidance for you as well.

​Read more:​ Alkaline Foods for Breakfast

What about the health benefits promised by an alkaline diet? One of the most common promises made about this type of diet is that it can help you fight cancer. But as Roberts with UC San Diego explains, the highest nutritional priority for people with cancer is often maintaining their current body weight by taking in enough calories and protein.

That doesn't necessarily exclude eating a diet made up largely of fruits and vegetables, which is a key recommendation for both preventing cancer and achieving an alkalizing diet. However, in a systematic review published in a 2016 issue of ​BMJ Open​, the authors note that there is almost no research at all to support (or disprove) the efficacy of a diet based strictly on the acid-alkaline principle for fighting cancer.

With that said, the kidneys' ability to regulate acid/base balance slowly declines with age. An analysis published in the May 2018 issue of ​Journal of Renal Nutrition​ posits that an alkaline diet may be useful for patients with chronic kidney disease, because it reduces the acid load on your kidneys.

Preserving bone is a key potential benefit of this sort of diet, although the authors of a thoughtful review of data published in the April 2018 issue of ​Nutrients​ argue that negative bone effects from an acidic diet are a subject of some controversy.

They note that proponents of alkalizing supplements argue that an overly acidic body leads to bone loss, with the minerals being depleted to buffer those acid levels. However, opponents of that philosophy maintain that if this were in fact the case, the body's bone minerals would be exhausted within just a few years.

Overall, the authors suggest that these points of view can be brought together under the theory that young people with healthy renal function are better able to manage a diet high in acid precursors, while older subjects with diminished renal function could benefit from an alkaline diet or alkalizing therapies.

Researchers are slowly exploring the question of whether an alkalizing diet may offer health benefits beyond reducing the load on your kidneys and preserving bone mass. One of the highest-quality scientific inquiries into this matter comes from a study published in the March 2008 issue of the ​American Journal of Clinical Nutrition.​

There, researchers evaluated 384 subjects of both genders, all 65 years or older, during a three-year trial. They concluded that increasing your intake of alkali-producing fruits and vegetables, especially those rich in potassium, may help preserve muscle mass in older adults.

Finally, the authors of the ​Journal of Environmental and Public Health​ article note that an alkalizing diet may help improve a variety of health outcomes and mitigate chronic diseases — but they attribute this largely to improvements in nutrient intake and mineral balance. Increasing your intake of fruits and vegetables is a simple way to achieve similar improvements.

However, most claims about the health benefits of alkalizing diets have yet to be convincingly confirmed — although the benefits of eating more fruits and vegetables, a common feature in any alkalizing diet, are so roundly accepted that they have been a key tenet of healthy eating for decades.

​Read more:​ List of High Alkaline Vegetables

Getting back to the vegetable at hand, potatoes are themselves mildly acidic, but they have an alkalizing effect on your body. They're also enormously popular — according to the most recent statistics available from the USDA, potatoes were the most commonly consumed vegetable in 2017.

But as the Harvard T.H. Chan School of Public Health warns, there's a problem with potatoes: They're rich in the type of readily digestible carbohydrates that cause your blood sugar and insulin levels to spike and then dip. Or to put it another way, potatoes have such a high glycemic load that they have the same effect on blood sugar that you'd get from a can of cola or a handful of jelly beans.

The potato's glycemic load is so high, in fact, that they don't count as a vegetable on Harvard's Healthy Eating Plate.

Aside from leaving you feeling tired, the school warns that this pattern of blood sugar dips and spikes can also prompt overeating by making you feel hungry soon after you eat. The school also warns that over the long term, this sort of high-glycemic diet can contribute to health problems such as obesity, diabetes and heart disease. There have even been a handful of studies linking increased potato consumption to weight gain and a higher risk of diabetes.

That's not to say having potato dishes occasionally is bad for you. As always, moderation is the key to keeping your body, health and weight in balance while still enjoying your favorite foods. Potatoes are also a good source of several nutrients, including potassium and vitamin C. According to the USDA, a medium baked russet potato, with the skin on, has 952 milligrams of potassium and 14.4 milligrams of vitamin C.

However, you can get even more nutrients from other foods without incurring that high glycemic load. For example, the USDA notes that a 3/4-cup serving of steam-in-bag broccoli florets contains a whopping 78 milligrams of vitamin C. The USDA also notes that a 1-cup serving of boiled white beans contains a remarkable 1,000 milligrams of potassium.

If you're choosing potatoes for their texture or their place as a starchy side dish, consider mixing up your potato intake with a few substitutes suggested by the Harvard T.H. Chan School of Public Health. These include whole grains, such as brown rice and quinoa. Or you can experiment with hulled barley, millet and other whole grains — you might find that you enjoy their taste and texture.

Other suggestions include beans as a side dish, or a combination of beans and whole grain rice; or try using cauliflower, which in recent years has become an immensely popular stand-in for starchy side dishes. You can buy it already prepped to make instant "cauliflower mash" or "riced cauliflower," or you can try making a few cauliflower recipes from scratch.