The Acid-Alkaline Debate: Why You Should Think Twice Before Checking Your Urine

We’re going to answer an important question today concerning a topic that gets a lot of attention in the alternative world, can urine pH be used as an accurate indicator of overall body pH? And more importantly, can you alter the body’s pH to a meaningful degree based on the foods you eat? I intend to answer these questions and more as well as provide a detailed physiological explanation to back up my position. Unfortunately, most of the arguments attempting to dispute these claims fail to adequately explain the mechanisms involved in pH regulation. So first, let’s define what pH is and what it means. Potential of hydrogen (aka pH) refers to the amount of hydrogen ions present in a solution. It measures on a logarithmic scale from 0-14 in which 7 is considered neutral, below 7 is considered acidic, and above 7 is considered alkaline. So the more hydrogen ions in solution, the lower the pH. This will be important to understand for the content contained later in this article as the body has several mechanisms it utilizes to maintain a strict blood pH of 7.35-7.45.

What They Got Right

It is true the foods we eat can in fact change our urine pH. Every food leaves behind an acid or alkaline ash. The relative acidity or alkalinity is determined by the amount of acid-forming constitutes such as sulfur and phosphate, and alkalis such as calcium, magnesium, and potassium.  This will change the amount of hydrogen ions the kidney needs dispose of, and thus will have an effect of the pH of the urine. The theory goes if we consume a diet rich in alkaline-forming foods such as fruits and vegetables as opposed to acid-forming foods like animal products and grains, then this will beneficially affect the pH of our blood.

Is Alkaline Always Better?

Before we proceed any further, I think it’s important to answer the question: Is being alkaline always better? Proponents of an Alkaline Diet argue that as we become more acidic (based on our urine pH), we become more susceptible to infection and disease. Is this true though? Is alkaline always better? Let’s look at a few examples to determine if we should hop on the alkaline bandwagon.

How about the stomach? Do we want our stomach to be alkaline? Of course not. Without sufficient stomach acid, it would be nearly impossible to adequately digest protein. This is a pretty big deal considering protein is an essential building block of life. Not to mention, the less acidic our chyme (food +  digestive juices) is, the slower our stomach will empty (allowing the potential of fermentation and purification to take place via microbes), and the less pancreatic enzymes and bile that will be released to perform the second stage of digestion. This is a prime reason why you should never drink with meals, because it dilutes the acidity in the stomach necessary to digest protein, ionize minerals (preparing them for absorption), and kill pathogens such as bacteria or parasites lingering on our food. Without this acidic barrier we set ourselves up for a host of nutritional deficiencies and intestinal infections. This is one of the reasons I’m so strongly against the use of pharmaceutical proton pump inhibitors (PPI’s) because of the inevitable negative long-term effects that will eventually result from chronic use of these medications.

What about the small and large intestines? Well it turns out these tissues also benefit from maintaining a slightly acidic pH. Many of the pathogenic bacteria and fungi we encounter tend to thrive at a pH that is typically more alkaline than normal pH of the intestines. This is because our guts contain a wide variety of acid-forming bacteria that help to create an unfavorable environment for these pathogenic organisms.

Then of course we have the acid mantel of the skin. This hydro-lipid “barrier” is made up of secretions from both the sebaceous and sweat glands, as well as acids created by endogenous flora that populate our skin’s surface. Its primary function is to limit the growth of pathogens such as certain types of fungus and bacteria and to also prevent the skin from cracking, which can leave the skin vulnerable to infection. A healthy skin pH sits at about 5.5. If this pH is significantly disrupted, as in the case of chronic hand-washing with highly alkaline soaps, unfavorable microbes and allergens can penetrate the skin’s surface and cause adverse reactions

pH Balance 101

So does urine pH tell us anything useful? Yes and no. Yes it can tell us that our kidneys are in fact functioning, but making any assumptions beyond that are simply unfounded and have no scientific basis for which to stand on. Allow me to explain why. As I eluded to earlier, the pH of the blood and most tissues in the body must be maintained within a tight window of 7.35-7.45. If pH drifts too far outside that window, protein denaturation (unfolding) can result. Since most enzymes are proteins, and nearly every reaction that takes place within our body requires an enzyme(s) to carry out, if severe enough, the results of lowered enzyme activity can be fatal.

Let’s first start off by looking at what types of acids the body has to deal with on a daily basis. We can split these into two categories; fixed acid and volatile acid. Fixed acids are also known as metabolic acids because they are produced as a byproduct of metabolic processes throughout the body. Common fixed acids include: lactic acid (or rather lactate and H+) produced as a result of anaerobic respiration, phosphoric acid derived from nucleic acid metabolism, and ketoacids from fat metabolism. Volatile acid is produced when water and carbon dioxide combine to form carbonic acid. This reversible reaction is mediated by an enzyme called carbonic anhydrase, which is a zinc-dependent metalloenzyme. Carbonic acid then rapidly dissociates into a hydrogen ion and a bicarbonate ion. Below we can see the equation:

Equation 2

It is important to note, that although fixed and metabolic acids are different compounds, ultimately what makes them “acids” is their ability to release hydrogen ions (H+) into solution. When acids (H+) are present throughout the blood and tissues, our body relies on three separate buffering systems to deal with this:

  • The protein buffering system in which the terminal ends or R-group of amino acids can either accept or release hydrogen ions in order to regulate overall concentration. This system is utilized in both the blood plasma and inside cells. The protein hemoglobin, which is the oxygen-carrying component of red blood cells, is a good example of a common protein buffer.
  • The phosphate buffering system in which phosphate ions (PO43-) can combine with hydrogen ions (primarily within cells) to form either hydrogen phosphate (HPO42-) which is a weak base or dihydrogen phosphate (H2PO4) which is a weak acid. This is the main system used to buffer metabolic acids since there is a relative abundance of phosphate ions present in intracellular fluid.
  • The bicarbonate buffering system in which bicarbonate ions (HCO3) combine with hydrogen ions (H+) to form carbonic acid (H2CO3) which is a weak acid. Carbonic acid (H2CO3) can then be turned back into carbon dioxide (CO2) and water (H2O). Carbonic acid (H2CO3) can also combine with hydroxide ions (OH) which are extremely basic (alkaline) and form bicarbonate (HCO3) and water (H2O). This is the most important buffering system present in the blood and other extracellular fluids.

The main difference then, is in the way in which we dispose of these two categories of acids. Fixed acids, or metabolic acids, are tightly regulated by the kidneys. When we take in acids from our food, or generate acids from our metabolism, the kidneys respond by eliminating excess acids (H+) and reabsorbing bicarbonate ions (HCO3) along the entire length of the nephron tubules. If this is still insufficient in dealing with the net acid load, we have another mechanism by which we can alter the concentration of acids and bases. Each nephron collecting duct is equipped with two different types of specialized cells: type-A intercalated cells and type-B intercalated cells. Both of these cells types have the ability to take water and carbon dioxide and use them to synthesize hydrogen and bicarbonate ions (via the zinc-dependent carbonic anhydrase). If we consume a diet rich in acid-forming foods, type-A intercalated cells will synthesize and excrete hydrogen ions into the urine while reabsorbing bicarbonate back into the blood. Conversely, if we consume a diet rich in alkaline-forming foods, type-B intercalated cells will synthesize and excrete bicarbonate ions into the urine and reabsorb hydrogen ions back into the blood.

So no matter what our dietary input is in terms of acid or alkaline, our bodies will fight to keep our physiologic pH within the window of 7.35-7.45.

Volatile acids are disposed of in a different fashion. We can see from the equation above that as the amount of carbon dioxide increases, the amount of carbonic acid and thus hydrogen ions also increases. Therefore, the more carbon dioxide we have present in our blood, the more acidic the pH of our blood will be. So in order to regulate the amount of carbon dioxide in the blood, humans have devised an ingenious mechanism: it’s called breathing. Breathing is a two-stroke process, we breathe in to take in oxygen, and we breathe out to get rid of carbon dioxide. Therefore, we can adjust respiratory (breathing) rate to compensate for changes in pH. Increasing respiratory rate increases the amount of CO2 blown off, effectively increasing the body’s pH (more alkaline). Likewise, decreasing respiratory rate decreases the amount of CO2 blown off and thus increases the amount of COretained within the blood, causing a decrease in pH (more acidic).

This system can compensate rather rapidly in cases of low to moderate changes in pH level. The kidneys then adjust over the next hours and days in response to changes in levels of metabolic wastes. There are some instances where this system is insufficient at compensating for large pH swings such as when diabetics enter into metabolic acidosis (in which the buildup of ketoacids result from the rapid conversion of fatty acids into energy when the body is starved of glucose), but this is a rare occurrence. The vast majority of the time, increasing ventilation (breathing) rate to get rid of extra carbon dioxide (and thus carbonic acid) can compensate for the increased acid load while the kidneys slowly take care of the rest.


I think I’ve clearly shown that it is not feasibly possible to influence the pH of the blood based on the foods we consume in our diet. This doesn’t give people a free ride to cut fruits and vegetables completely out of their diet as there are a plethora of other reasons to consume these foods. I’m still an advocate of a diet that contains mostly plants and some animal products, but I don’t believe that reasoning should be based on whether these foods have an effect on our pH or not. It’s dangerous to put something like “alkaline water” (which is harmful in its own right) in the same category as eating fruits and vegetables. These two things should be mutually exclusive from one another.

Additional Sources

The Acid-Alkaline Myth: Part 1  (Good explanation of the alkaline/osteoporosis link)

The Acid-Alkaline Myth: Part 2  (Touches on alkaline/cancer link)

Great video highlighting various questions and myths concerning the alkaline debate

A podcast analyzing the three basic claims of the acid-alkaline hypothesis

Quick video by Dr. Tel-Oren explaining respiratory and kidney regulation of pH


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