One of the most common misconceptions about body chemistry is that consuming alkaline or basic foods and fluids can influence the pH of the body—this is untrue. By learning more about homeostasis and acid/base chemistry, one can better understand how the human body self-regulates internal pH.
Understanding the human body as a whole system is an important starting point. The system contains many parts including digestive, nervous, respiratory and urinary. Together they must all communicate with each other in order to maintain conditions that are favorable for sustaining the body’s cells and, as a whole, the entire system.
This concept, known as homeostasis, encompasses the regulation of bodily variables such as levels of oxygen and carbon dioxide, temperature, pH, blood pressure, fluid volume, and nutrient concentration. It is essentially a feedback system that is constantly changing based on internal and external factors. A prime example of this compensation is body temperature. When we get too hot, we sweat, and our skin pores dilate. When we get too cold, we shiver, which increases internal heat by small muscular contractions, and our skin pores constrict.
The circulatory system is largely responsible for shuttling water, nutrients, oxygen, and waste throughout our body. Because our body consists mostly of water, we are particularly concerned with conditions associated with it. In the context of alkalinity, we focus on pH, which directly reflects the acidity or alkalinity of the aqueous fluids in our body.
When we discuss acids and bases, we are discussing compounds that can donate H+ (acids) or accept H+ (bases). The pH scale is typically defined from 0 to 14; however, it can be negative or higher than 15. A pH of 7 is regarded as neutral, and is representative of pure water. Solutions with a pH less than 7 are referred to as acidic. Those with a pH higher than 7 are defined as basic, or alkaline.
Finally, acids and bases can be classified as weak or strong based on how much H+ is donated or accepted. Strong acids donate more H+ than weak acids; strong bases accept more H+ than weak ones. Acids and bases and their salts are the basis of buffers, which are solutions that maintain a target pH upon the addition or subtraction of H+.
Acids and bases yield solutions with pH values on a spectrum, on either side of the pH value defined as neutral for that system. In the human body, the average pH of blood is 7.4, and thus a pH less than 7.4 is referred to as acidic and a pH greater than 7.4 is referred to as basic/alkaline.
The pH range for sustaining life is 6.8 to 8.0. When blood pH falls below 7.35, the system is in acidosis; when pH is above 7.45, it is in alkalosis. Both conditions are life threatening and negatively affect the central nervous system. A system in acidosis leads to depression of the system; while one in alkalosis leads to excitation of it.
Where does this acid in the body come from? One source is from the metabolism of nutrients, a reaction from which carbon dioxide is produced. Carbon dioxide in liquid solution forms carbonic acid, which is a weak acid. Another source is from the digestion of sulfuric and phosphoric compounds, typically found in meat. These compounds form stronger acids within the body.
Conversely, digestion of fruits and vegetables yield bases that result in a net contribution of H+ to the system. This drives it to the acidic side. Finally, H+ is produced during normal cellular metabolic functions, such as when fats are metabolized or lactic acid is produced during intense exercise.
Finally, one of the causes of metabolic alkalosis is the ingestion of alkaline chemicals such as sodium bicarbonate, also known as baking soda. Alteration of the stomach pH relieves bothersome symptoms, but results in a shift in the carbonic acid/bicarbonate buffer equilibrium—which is not desirable.
The human body has numerous integrated components that work together to maintain a system-wide state that functions optimally to sustain life. There is a narrow pH range for sustaining life, and the body self-regulates pH through chemical buffers, respiration, and the kidneys. The consumption of foods and fluids within a wide pH range do not affect the pH of the human body to any significant extent due to the compensatory mechanisms that exist in the human body.
Moral of the story: if you insist on drinking alkaline fluids, save your money and drink Austin tap water! On average, the pH is around 9.7. You can find the quarterly water quality summaries on the City of Austin’s website.
It should be clear that the human body has mechanisms in place to regulate pH, and that external factors, such as the ingestion of “alkaline” foods or high-pH fluids, cannot affect this variable to any significant extent. These bodily mechanisms instead include chemical buffers, the respiratory system, and the kidneys.
There are four different buffer systems in the human body which regulate [H+].
The primary one is the carbonic acid/bicarbonate buffer pair.
The respiratory system and the kidneys work together here by controlling intake of carbon dioxide and excretion of bicarbonate.
The secondary buffer systems, which deals with protein, hemoglobin, and phosphate, work with the carbonic acid/bicarbonate system to provide additional resources for maintaining optimal pH.