Can Fasting Cause Low Bicarbonate Levels?

January 9, 2026 •

4 min read

According to a 2019 study published by the National Institutes of Health, prolonged fasting can induce a state of starvation ketoacidosis, which can cause low bicarbonate levels. This metabolic shift occurs when the body, deprived of glucose, begins to break down fat for energy, producing an excess of ketones that overwhelms the body's buffering capacity.

Quick Summary

This article explains the physiological mechanisms linking fasting to decreased bicarbonate stores, primarily through the process of ketogenesis. It details the resulting metabolic acidosis, outlines the symptoms of low bicarbonate, and differentiates between normal ketosis and dangerous ketoacidosis.

Key Points

Fasting Triggers Ketogenesis: When fasting, the body switches to using fat for energy, a process called ketogenesis, which produces acidic ketone bodies.
Ketones Lower Bicarbonate: The body's bicarbonate buffer system uses up its reserves to neutralize the acidic ketones, leading to a decrease in serum bicarbonate levels.
Mild vs. Severe Acidosis: In healthy people, fasting leads to mild ketosis. However, in vulnerable individuals like diabetics, it can escalate to severe ketoacidosis.
Prolonged Fasting Increases Risk: The risk and severity of low bicarbonate increase with the duration of the fast, as the body produces more ketones over time.
Hydration is Crucial: Staying well-hydrated during fasting helps the kidneys flush out excess acids and supports the body's natural acid-base balance.
Underlying Conditions Worsen Risk: Pre-existing conditions like diabetes and kidney disease significantly increase the risk of developing serious metabolic acidosis from fasting.

The Metabolic Shift: How Fasting Induces Ketogenesis

When an individual begins fasting, the body quickly uses its stored glucose for energy. After approximately 12–14 hours, or when carbohydrate intake is significantly reduced, the body transitions into a state of ketogenesis. This is a normal and adaptive process where the liver begins to break down fat for fuel, producing compounds known as ketone bodies (beta-hydroxybutyrate, acetoacetate, and acetone). While ketones serve as an efficient alternative energy source for the brain and other tissues, they are also acidic.

The Bicarbonate Buffer System and Its Role

The body maintains a tightly regulated blood pH balance (typically between 7.35 and 7.45) using a buffer system, with bicarbonate ($HCO_3^-$) being the primary buffer in the blood. This system neutralizes acids to prevent the blood from becoming too acidic (acidosis) or too alkaline (alkalosis). When ketones accumulate during fasting-induced ketogenesis, the body's bicarbonate reserves are consumed to neutralize these acids, leading to a mild decrease in serum bicarbonate levels.

Normal Ketosis vs. Ketoacidosis

It is critical to distinguish between physiological ketosis, a normal metabolic state during fasting or a ketogenic diet, and ketoacidosis, a dangerous and uncontrolled medical condition. In healthy individuals, the body's compensatory mechanisms, including increased respiratory rate and renal function, typically manage the excess acid, keeping blood pH within a safe range, albeit with a slight reduction. Starvation ketoacidosis, while presenting with low bicarbonate, is usually less severe than diabetic ketoacidosis, with blood pH often remaining above 7.3. In contrast, in conditions like untreated Type 1 diabetes, insulin deficiency leads to uncontrolled fat breakdown and a massive production of ketones, overwhelming the body's buffering systems and causing severe metabolic acidosis.

Factors Influencing Bicarbonate Levels During Fasting

Duration of Fasting: The length of the fast directly correlates with the degree of ketosis and the decline in bicarbonate. Longer fasts deplete glucose reserves more thoroughly, increasing fat metabolism and ketone production.
Health Status: Individuals with underlying conditions, especially kidney disease or diabetes, are at a much higher risk of developing significant and dangerous metabolic acidosis. The kidneys play a vital role in acid-base balance by excreting excess acid and regenerating bicarbonate, a function that is impaired in chronic kidney disease.
Hydration: Dehydration during fasting can exacerbate acidosis by concentrating the blood and impairing renal function, making it harder for the body to excrete excess acid.
Medications: Certain medications, such as some diuretics or anti-epileptic drugs like topiramate, can affect electrolyte balance and increase the risk of low bicarbonate.

Symptoms of Low Bicarbonate

Symptoms of low bicarbonate, a condition known as metabolic acidosis, can range from mild to severe depending on the degree of acidosis. Mild cases may have few noticeable signs, but as bicarbonate levels drop further, the body's regulatory systems become strained. Common symptoms include fatigue, nausea, vomiting, confusion, and a rapid, deep breathing pattern (known as Kussmaul breathing).

Comparison: Starvation Ketosis vs. Diabetic Ketoacidosis


Feature	Starvation Ketosis	Diabetic Ketoacidosis (DKA)
Cause	Prolonged fasting or very low carbohydrate intake in non-diabetic individuals.	Severe lack of insulin in individuals with diabetes, primarily Type 1.
Ketone Levels	Elevated, but typically not to dangerous levels in healthy individuals.	Very high and uncontrolled, leading to extreme acid buildup.
Glucose Levels	Low blood glucose (hypoglycemia).	Very high blood glucose (hyperglycemia) due to lack of insulin.
Acidosis Severity	Mild to moderate; blood pH generally remains above 7.3.	Severe metabolic acidosis, with blood pH potentially dropping below 7.1.
Treatment	Refeeding and gradual nutritional reintroduction.	Requires urgent medical treatment, including insulin and intravenous fluids.

Management and Prevention

For those engaging in routine or intermittent fasting, maintaining adequate hydration is paramount to support kidney function and help manage the metabolic changes. Listening to your body is crucial; severe or concerning symptoms like persistent nausea, confusion, or difficulty breathing warrant immediate medical attention. For individuals with pre-existing conditions like diabetes or kidney issues, fasting should only be undertaken with strict medical supervision due to the heightened risk of serious complications.

Conclusion

Yes, fasting can cause low bicarbonate levels, particularly during prolonged periods, due to the metabolic shift towards ketogenesis. For most healthy individuals, this results in mild, self-limiting ketosis that is well-tolerated and resolves with refeeding. However, in people with underlying health issues like diabetes, or in cases of extreme, prolonged fasting, it can progress to the more severe and life-threatening condition of ketoacidosis. Understanding the difference between these states and recognizing warning signs is key for anyone considering extended periods of fasting. Always consult a healthcare provider before beginning any prolonged fast, especially if you have chronic health conditions.

For further information on metabolic acidosis and its causes, refer to this comprehensive guide from the Cleveland Clinic.

Frequently Asked Questions

Significant decreases in bicarbonate levels usually occur after prolonged fasting, when the body has fully transitioned into ketogenesis and the bicarbonate buffer is being utilized to neutralize acidic ketones.

Ketosis is a mild, controlled metabolic state where ketone bodies are used for fuel, typically resulting in a slight drop in bicarbonate. Ketoacidosis is a dangerous, uncontrolled state, often in diabetics, where excessive ketones lead to severe metabolic acidosis.

In healthy individuals, mild reductions are generally not dangerous. However, if acidosis becomes severe or occurs in those with underlying conditions like diabetes or kidney disease, it can cause severe health complications and requires urgent medical treatment.

Symptoms of severe metabolic acidosis include extreme fatigue, nausea, confusion, a rapid heartbeat, and rapid, deep breathing (Kussmaul respiration).

Ensuring adequate hydration is the most important step. For prolonged fasts, medical supervision is recommended, especially if you have pre-existing health conditions. Gradual reintroduction of food after a long fast helps restore balance.

Prolonged fasts and very low-carbohydrate diets, such as the ketogenic diet, are most likely to induce the level of ketogenesis that affects bicarbonate. Intermittent fasting typically does not cause significant metabolic changes in healthy individuals.

Administering bicarbonate is not recommended without medical guidance, as it can disrupt the body's compensatory mechanisms and potentially cause electrolyte imbalances.