You might have heard that plant foods are good for the kidneys. Rich in fiber, vitamins, minerals, and antioxidants — they provide SO many benefits for your kidneys and overall health!
Another benefit that’s not as commonly discussed is something called PRAL. PRAL stands for Potential Renal Acid Load. What exactly is this and how does it relate to the kidneys? To start, let’s review how your kidneys work.
Review: How The Kidneys Work
The kidneys are two small organs that perform many different functions in the body. Some of the key functions of the kidneys include:
- Removing toxic waste and excess fluids
- Kicking off production of red blood cells
- Helping to regulate blood pressure
- Producing hormones
- Retaining the right balance of important nutrients & minerals
- Regulating body’s acid-base balance
Take special note of that last one – regulation of acid-base balance.
Acid-base balance is a state of equilibrium in the body and the bloodstream. “Equilibrium” essentially means that the things that are supposed to be balanced are, in fact, balanced.
Scientifically speaking, acids are compounds that can donate a hydrogen ion to another compound. Bases (also referred to as alkali molecules or compounds) are able to accept hydrogen ions from other compounds. In short, acids are hydrogen donors while bases are hydrogen accepters.
Your body needs to have the right balance of acid and right amount of base in order to function properly. As mentioned above, the kidneys help to maintain this balance. The lungs play a role in this as well.
We can measure the acid-base balance by looking at the pH of the blood. pH is a scale that measures how acidic or how basic something is. The pH scale ranges from 0 (very acidic) to 14 (very alkaline). Blood is maintained between 7.35-7.45 – right in the middle of the pH scale. It is vital for the body to maintain this range for the body to do all the things it need to do!
Not surprisingly, some serious problems can begin to occur when the acid-base balance in the body gets thrown off.
Acidosis: A Big Problem
As I mentioned, the acid-base balance in the body needs to stay within a tight range. Unfortunately, one consequence of decreased kidney function is that the kidneys struggle to excrete acid and maintain the right balance – leading the blood to become more acidic. This is a condition known as metabolic acidosis, or just acidosis.
What are some consequences of acidosis? Acidosis has been associated with a whole slew of health problems, including:
- bone loss, or osteoporosis
- worsening kidney disease
- muscle loss and wasting
- endocrine problems
- poor blood sugar control
- hyperkalemia (high blood potassium)
Yep, those are all things you want to avoid. Acidosis would be identified on your labs by a low serum bicarbonate level. Patients are often prescribed a medication called sodium bicarbonate to correct this. (But, spoiler alert, the food you eat plays a role in this too.)
What Contributes To Acidosis?
Poor kidney function is a contributor to acidosis, like we just discussed. This is because the kidneys can’t get rid of excess acid in the body, the way it’s supposed to.
But how did that acid get there in the first place?
Well, most actually comes from foods. And PRAL measures the amount of acid from foods that the kidneys have to deal with.
How Is PRAL Value of a Food Determined?
How do you know which foods are more acid-producing or alkali-producing? It’s determined based on the nutrients found in the food.
Foods that are high in protein, phosphorus, and sodium contribute to a higher PRAL value. A higher PRAL means a food is more acid producing. Higher PRAL foods will have a positive value, greater than 0.
On the flip side, foods that are higher in potassium and magnesium have a lower PRAL. A lower PRAL means a food is more alkalinizing. Low PRAL foods will have a negative numeric value, such as -5.0.
There is a formula used to calculate this: 0.49 x protein (g) + 0.037 x phosphorus (mg) – 0.021 x potassium (mg) – 0.026 magnesium (mg) – 0.013 x calcium (mg).
Quite cumbersome, I know! Luckily you don’t have to calculate this out yourself for every food; online tables of foods and their PRAL values exist. You can also use the premium version of the app Cronometer to see the PRAL values for foods you eat.
I have also created a PRAL calculator you can use to try out some calculations yourself, if that sort of thing is interesting to you!) (go to File → Download in order to download and use the calculator)
PRAL & pH: Different Ways To Measure Acidity
Quick sidebar before we continue, as I have to make an important distinction!
If you hear the words “acid” and “food” you might immediately start thinking of tomatoes, lemons, coffee, etc. But, these foods don’t necessarily increase the acid load that the kidneys have to handle. What is the difference?
Foods like tomatoes and lemons are acidic in the sense that they have an acidic pH. pH, as you’ll recall, is the measure of acidity or alkalinity of a solution or a food. You might even feel the acidity of these foods in your esophagus or stomach.
However, when talking about acid load on the kidneys – this is a totally concept different! Potential Renal Acid Load (or PRAL) has nothing to do with the pH of a given food. Instead, the acid load or PRAL is a measure of the acidifying or alkalinizing effect of a food on the body. And more acid translates to more work for the kidneys.
Comparing PRAL vs. pH of A Specific Food
Again, PRAL is based on the nutrients in foods, and the acid/base changes those nutrients bring about in the bloodstream. The pH of the food itself has no bearing on the acid load of the food once its nutrients hit your bloodstream.
A great example of this is lemons. Lemons have a pH of 2, which is quite acidic.
But the PRAL value of a lemon equals -2.313 (I calculated this using nutrition data from the USDA FoodData Central database). Foods with a negative PRAL value are alkali-producing, as you’ll recall from above.
When you consume lemon, it may TASTE acidic, but it has an alkalinizing effect in terms of your body chemistry.
Now, back to the acid from the foods you eat. If it’s not coming from tomatoes, lemons, and coffee (because now you know those foods are “acidic” in a different sense!), where do you get dietary acid?
Foods That Result In A High Dietary Acid Load
Think about how PRAL is calculated – it’s based on the protein, phosphorus, and sodium content of the food. You may not be surprised to see that the following types of foods (which tend to be higher in protein, phosphorus, and sodium) result in a higher dietary acid load:
- meat, poultry, fish
Some other foods that also have a positive (acid-producing) PRAL, but to a lesser extent, include:
- most nuts, seeds, and nut butters
- milk and yogurt
- most grain products such as rice, cereal, and bread
Now let’s be clear about something. A positive PRAL value does not necessarily mean a food is “bad.” A food’s PRAL value is a piece of data you have at your disposal, that could potentially be a helpful decision making tool in determining what foods to limit and what foods to eat more of. But it’s not the end-all-be-all of whether or not to eat any given food. We can’t reduce the health value of a food down to a single number – there’s a lot more nuance than that!
So, instead of thinking about the PRAL of a single food item, it might be more helpful to think about the PRAL of your overall diet. You’re not going to avoid foods with a positive PRAL. You just need to eat enough foods with a negative PRAL to balance those out and reduce the acid load on the kidneys!
So which foods have a negative, alkali-producing PRAL value?
Foods With A Low Dietary Acid Load
Think back to the PRAL formula again. More potassium and magnesium contribute to a negative PRAL value. Foods that tend to be higher in potassium and magnesium (and therefore have a negative, alkali-producing PRAL value) include…
- some nuts such as macadamia
- some seeds such as pumpkin
- fresh spices and herbs
These foods are less work for the kidneys to handle. They balance out the more acid-producing foods that you eat.
The Typical American Diet Is A High Acid Diet
When you think of the “typical American diet,” what comes to mind? Burgers? Hot dogs? Chips? Those are some of the first things that may pop into your head.
The typical American diet tends to be high in protein foods, processed foods, and refined grain products. It tends to be low in fruits, vegetables, and legumes.
Therefore, when looking at the overall PRAL value of the typical American diet, you might not be surprised to learn it leans more acid-producing. One study from 2021 assigned individuals to eat either a vegan, plant-based diet or a meat-rich diet. The median PRAL value for the vegan diet was -23.57, whereas the median PRAL for the meat-rich group was 18.78. Other studies have similar findings.
Other studies have examined the health implications associated with a high PRAL diet. Higher PRAL diets have been associated with increased incidence of sarcopenia, low bone mineral density, hypertension, insulin resistance, chronic kidney disease, kidney stones, and cardiovascular disease and mortality.
A Kidney Friendly Diet is a Lower Acid Diet
Let’s circle back to the kidneys. A diet rich in high PRAL foods and low in negative PRAL foods is associated with poorer kidney health outcomes.
For better kidney health, a shift to eating fewer high PRAL foods (i.e. animal proteins and high sodium foods) and more negative PRAL foods (i.e. more fruits and vegetables) can make a big difference! And, thinking beyond the acid load alone, more fruits and veggies are also associated with better blood pressure and better blood sugar control – both beneficial outcomes in terms of the health of your kidneys.
So, how do you take all this information and apply it to what you eat? Well, you COULD meticulously add up the PRAL value of your entire diet – and again, an app like Cronometer will do the hard work for you. The goal would be for your overall daily food intake to result in a lower or negative PRAL value.
But you don’t even have to do that. Knowing that foods like fruits, veggies, and beans reduce your total dietary acid load, why not take a look at your current diet and look for opportunities to add more of these foods?
I like to have my clients do what I call a “diet audit.” Simply ask yourself, how often am I eating fruits? Or veggies? And be honest with yourself!
From there, make a plan to tweak things going forward. If you’re only eating veggies 1 day per week right now, start by adding 1 extra vegetable serving per week. If you’re already eating 1 serving of veggies per day, could you possibly bump it up to 2 per day?
It’s nothing earth-shattering – but turns out more fruits and vegetables are good for you. The dietary acid load is just another argument for including more of these types of foods in your diet.
To sum up what you’ve learned:
- The kidneys help regulate acid-base balance in the body
- Reduced kidney function means the blood can become more acidic, due to decreased ability of the kidneys to eliminate acid
- Diet is a major contributor to the acid load on the kidneys
- Acid load from foods is also referred to as Potential Renal Acid Load, or PRAL. PRAL is calculated with a formula that uses the protein, phosphorus, sodium, magnesium, and potassium content of a given food
- PRAL is different than the pH of a food. The pH of a food has no impact on the acid load on the kidneys
- Foods with a high PRAL include meat, poultry, fish, eggs, cheese
- Foods with a low-moderate PRAL includes nuts, seeds, grains, and dairy
- Foods with a negative PRAL include fruits, vegetables, and beans (plus a few types of nuts, seeds, and grains)
- The typical American diet is a higher acid diet, which is associated with health problems including kidney disease and kidney stones
- A lower acid diet is associated with better kidney health outcomes
- A kidney-friendly diet is a diet rich in plant foods
Ready to start eating more plants? I know it can feel overwhelming to think about, but start small. Focus on one food at a time, one meal at a time. It may feel minuscule in the grand scheme of things, but know you’re doing yourself and your kidneys a big favor every time you choose to eat more plants.
For more help and guidance personalized to you, consult with a Board Certified Renal Dietitian (like me!). I’m also on Instagram, TikTok, and Facebook dishing up helpful info and meal ideas to help you out in the meanwhile. Until next time, be well. — Kate, Your Kidney Dietitian