Ketosis is a metabolic state where the body shifts its primary fuel source from glucose to fat, leading to the production of compounds called ketone bodies. This state is typically induced by fasting, prolonged exercise, or following a very low-carbohydrate diet. The pH scale measures acidity, and human blood must stay between 7.35 and 7.45 for biological processes to function correctly. Understanding how the body manages this delicate pH balance while also producing acidic ketone bodies is crucial to clarifying the relationship between ketosis and changes in blood acidity.
How the Body Maintains Blood pH
Maintaining the blood pH within its tight range of 7.35–7.45 is a continuous and carefully regulated process. This stability is primarily managed by three interconnected physiological systems that work in sequence to neutralize or remove excess acids and bases. The fastest line of defense involves chemical buffers, which are substances in the blood that immediately bind to or release hydrogen ions to prevent dramatic shifts in acidity. The bicarbonate-carbonic acid buffer system is the most significant of these, rapidly converting strong acids into weaker ones.
The second regulatory system is the respiratory system, which controls blood acidity by adjusting the rate of carbon dioxide (CO2) expulsion. Carbon dioxide readily combines with water in the blood to form carbonic acid, which then dissociates into bicarbonate and hydrogen ions. If the blood becomes too acidic, the brain signals the lungs to increase the depth and rate of breathing, a process called hyperventilation, to rapidly eliminate more CO2. This quick expulsion of CO2 decreases the concentration of carbonic acid, thereby raising the blood pH.
The third system, the renal system, provides the most powerful long-term control over blood pH. The kidneys act more slowly than the buffers and lungs, taking hours to days to fully compensate for imbalances. They regulate acidity by selectively reabsorbing bicarbonate, a major base, and excreting excess hydrogen ions into the urine.
The Acidic Nature of Ketone Production
Ketone bodies are organic acids produced in the liver when fat is broken down for energy, a process called ketogenesis. This process begins with lipolysis, where fatty acids are released from fat stores and travel to the liver. Inside the liver cells, these fatty acids are converted into three primary ketone bodies: acetoacetate, beta-hydroxybutyrate (BHB), and acetone.
Acetoacetate and beta-hydroxybutyrate are the two main forms used as fuel by the brain and muscles. Both of these molecules are inherently acidic, meaning they release hydrogen ions into the bloodstream. Acetone is the third ketone body, formed as a spontaneous breakdown product of acetoacetate, but it is not acidic and is mostly exhaled or excreted in urine.
As these acidic ketones accumulate, the body’s compensatory mechanisms immediately activate to prevent a drop in pH. The respiratory system often responds by increasing breathing depth, which helps expel the acidic compound CO2. Acetone, being volatile, is also expelled through the breath, which can result in a distinct, fruity odor sometimes referred to as “keto breath”.
Differentiating Safe Ketosis from Dangerous Ketoacidosis
Nutritional ketosis is a mild, controlled metabolic state, often achieved through carbohydrate restriction or fasting, where blood ketone levels typically range between 0.5 and 3.0 millimoles per liter (mmol/L). In this state, the body’s buffer systems, lungs, and kidneys successfully neutralize the acids produced, keeping the blood pH stable within the normal range.
The body’s regulatory system, specifically the presence of insulin, prevents ketone production from running rampant. Even at low, healthy levels, insulin acts as a brake, ensuring that the liver does not overproduce ketones. This controlled environment prevents the level of acidic ketone bodies from overwhelming the body’s ability to excrete or neutralize them.
In contrast, diabetic ketoacidosis (DKA) is a severe condition that affects individuals with Type 1 diabetes due to a severe lack of insulin. Without sufficient insulin, the regulatory “brake” is removed, causing ketone production to skyrocket, often reaching extreme concentrations of 15 to 25 mmol/L. This massive, uncontrolled surge of acidic ketones overwhelms the body’s compensatory mechanisms, leading to severe metabolic acidosis. DKA is defined by a dangerously low blood pH, sometimes dropping below 7.0, and requires immediate emergency medical intervention.
Recognising Symptoms of Acid Imbalance
One of the most telling physical signs of failing acid-base balance is Kussmaul breathing, a pattern of deep, rapid, and labored breaths. The body uses this hyperventilation as a last-ditch effort to expel as much acid-forming carbon dioxide as possible.
Other symptoms often accompany this severe acid imbalance. The increased excretion of acetone can be detected as a fruity odor on the breath. Patients may also experience thirst, frequent urination, and nausea or vomiting, which contribute to dehydration. As the acidosis progresses, confusion, altered mental status, or drowsiness can set in due to the acid’s effect on brain function. These symptoms are indicative of a medical emergency, particularly in individuals with diabetes, and necessitate immediate hospital care.