Is It Dangerous to Have High Ketones While Fasting?

Fasting has profound health benefits as it promotes cellular repair, weight loss, and improved blood sugar control while reducing the risk of metabolic and cardiovascular diseases.

During fasting, the body shifts into ketosis, using ketones as its primary energy source. But is having high ketones while fasting dangerous? 

Discover the difference between ketosis and ketoacidosis and learn how to monitor your ketone levels effectively.

What are ketones?

Ketones, or ketone bodies, are organic acids produced from dietary fats or stored body fat that provide an alternative energy source when the body’s glucose levels are low.

Glucose, derived from carbohydrates and sugars, is the body’s primary fuel source. However, when carb intake is restricted, the body begins to burn fat, which releases large amounts of ketones.

As ketones start to build up in your bloodstream and begin to fuel your cells, your body enters a metabolic state known as ketosis. 

Ketosis can be induced by following a low-carb diet or practicing intermittent fasting, which restricts the intake of foods and calorie-containing beverages, forcing the body to burn fat to generate energy. 

Nutritional ketosis has impressive health benefits and is generally considered safe for most people. However, individuals with type 1 diabetes are at risk of excessive ketone production, which can have serious health consequences. 

Watch the video below to learn more about elevated ketone levels during fasting.

Ketosis vs. ketoacidosis

Diet-induced ketosis, also known as nutritional ketosis, is achieved by fasting or reducing daily carbohydrate intake to 50 grams or less, typically through a ketogenic diet.

Due to the caloric restriction associated with fasting, the body depletes available blood glucose and glycogen reserves, which triggers fat burning and, consequently, ketone production to supply cells with energy.

This natural rise in blood ketone concentrations ensures that the body maintains all physiological functions and isn’t associated with health issues. 

In contrast, ketoacidosis, also known as diabetic ketoacidosis (DKA), is a potentially life-threatening condition characterized by excessive ketone levels. 

Ketoacidosis typically occurs in individuals with uncontrolled diabetes, mostly resulting from missed insulin therapy, wrongly calculated insulin doses, or faulty insulin pumps. 

Lack of or inadequate insulin levels, especially in combination with high-carb meals, can trigger excessively high blood sugar levels and rapid fat breakdown, leading to a large release of ketones into the blood.  

“Insulin not only stabilizes your blood sugar level, but it also controls ketone production,” explains Dr. Berg. “If you don’t produce or administer enough insulin, too many ketones are produced, which can acidify the blood and lead to ketoacidosis.”

Ketones are acidic and can alter the blood's pH, which can negatively impact cellular function, nerve signal transmission, and overall metabolic health. 

According to the American Diabetes Association (ADA) DKA guidelines, common symptoms of ketoacidosis include:

• Extreme thirst

• Dry mouth

• Elevated blood sugar

• Fatigue

• Difficulty breathing

• Fruity-smelling breath

In severe cases, ketoacidosis can lead to confusion, loss of consciousness, and even coma, and it’s crucial to seek immediate medical attention to avoid serious health consequences. 

Though more common in type 1 diabetes, those with type 2 diabetes can also develop ketoacidosis if their bodies don’t produce adequate amounts of insulin or if their diabetes is poorly managed.

Causes of high ketones while fasting

Intermittent fasting (IF), which involves time-restricted periods of eating and fasting, is commonly paired with a ketogenic diet to maximize the health benefits of ketosis.

Because caloric restriction enhances the body’s fat-burning capacity, IF promotes nutritional ketosis, which can raise ketone levels to slightly higher concentrations than following a ketogenic diet alone. 

Prolonged fasting methods, such as abstaining from food for 24 or 48 hours, can trigger an even deeper state of ketosis. Extended fasting periods shift the body into more effective fat-burning and accelerated ketone production, which can result in elevated ketone concentrations in the blood and urine. 

This ketone-boosting effect of caloric restriction is even more pronounced after 72 hours of fasting. 

A study published in Nutrients found that after 12 days of fasting, consuming less than 250 calories daily, blood ketone levels reached four millimoles per liter (mmol/L) without producing ketoacidosis or other adverse effects. 

This suggests prolonged fasting with low or no calorie intake can produce elevated ketone levels, indicating the body's ability to safely adapt to extended periods of advanced nutritional ketosis.

Is it dangerous to have high ketones while fasting?

It's common to develop higher ketone levels in your blood while fasting compared to baseline levels, which are usually below 0.6 mmol/L.

Normal blood ketone levels associated with a ketogenic diet and intermittent fasting typically range between 0.6 to 1.5 mmol/L.

Ketosis may become dangerous when blood ketone concentrations exceed 3 mmol/L, which suggests an increased risk of ketoacidosis, especially in individuals with poor metabolic health or those with diabetes. 

However, in some instances, healthy adults who engage in extended fasting can reach ketone concentrations of up to 4 mmol/L without experiencing adverse side effects.

When evaluating elevated ketone levels, it’s crucial to consider the context, as nutritional ketosis is unlikely to lead to ketoacidosis. In contrast, for individuals with diabetes or poor metabolic health, elevated ketones could be a sign of a medical emergency. 

It’s recommended to consult with a healthcare provider if ketone levels rise above 3 mmol/L, especially if you're not following a ketogenic diet or practicing fasting.

How to test ketone levels

Urine or blood ketone tests can be administered to evaluate ketone concentrations in the body. 

Urine ketone test kits can be purchased over the counter to monitor levels at home, or you can request a blood ketone test from your doctor, which will provide more accurate results.

A urine ketone level below 0.6 mmol/L is generally considered normal, whereas levels between 0.6 and 3 mmol/L are generally seen in individuals who are fasting or following a ketogenic diet.

Ketoacidosis is typically diagnosed when urinary ketone concentrations rise above 3 mmol/L.

According to a study published in Current Nutrition Reports, “The hallmark of nutritional ketosis is blood ketone levels of 0.5 to 3 mmol/L. This is in stark contrast to, and should not be confused with, the pathophysiologic state of type 1 DKA, where the range of ketones present 5 to 10 fold greater than the levels achieved during nutritional ketosis.”

Those who are at risk of developing diabetic ketoacidosis should regularly monitor their blood glucose and ketone levels and consider starting a whole foods-based ketogenic diet, such as Healthy Keto®. 

Limiting carbohydrate intake can help stabilize blood sugar levels, reducing the need for insulin and potentially reducing the risk of ketoacidosis. 

However, it’s crucial that individuals with diabetes consult a healthcare provider to discuss any dietary changes that may require adjustments to insulin dosages.

Key takeaways

Fasting prompts the liver to convert fat into ketones. While this natural process supports energy production during caloric restriction, you may wonder if high ketones are dangerous. 

No, elevated ketone levels aren’t dangerous if induced through fasting and differ significantly from ketoacidosis, a serious complication linked to uncontrolled diabetes due to an insulin deficiency.

While blood ketone levels between 0.6 and 3 mmol/L are typical while fasting, levels higher than 3 mmol/L can indicate an increased risk of ketoacidosis, especially in individuals with diabetes.

FAQ

1. What causes high ketones while fasting?

During fasting, the liver breaks down body fat to generate energy. This releases large amounts of ketones, a group of organic acids that serve as an alternative fuel source during caloric restriction. 

Longer fasting periods trigger accelerated fat loss, which explains why prolonged fasts can lead to high ketone levels.  

2. What happens if my ketones are high?

Blood ketone levels between 0.6 to 1.5 mmol/L and urine ketone concentrations between 0.6 and 3 mmol/L are normal and safe while fasting. 

Ketone levels higher than 3 mmol/L can indicate ketoacidosis, which may be life-threatening. However, ketoacidosis typically only affects individuals with poorly controlled diabetes, and fasting-related ketosis is generally not associated with dangerously elevated ketone levels. 

3. Can you have high ketones without diabetes?

Yes, ketones can be higher than usual if you follow a ketogenic diet or are fasting. These practices shift the body into a fat-burning state, also known as ketosis, which triggers the release of ketones.

Ketosis is different from diabetic ketoacidosis, which is a life-threatening condition that primarily affects individuals with uncontrolled diabetes.

4. Do high ketones mean ketoacidosis?

No, high ketones don’t always indicate ketoacidosis. Blood ketone levels between 0.6 to 1.5 mmol/L and urine levels between 0.6 and 3 mmol/L fall within the normal range while fasting or following a keto diet. 

Ketone levels significantly above 3 mmol/L, particularly in individuals with diabetes, suggest an elevated risk of ketoacidosis and warrant immediate medical attention.

5. How do I test my ketones while fasting?

Ketone levels can be measured through either urine or blood tests. Urine tests are widely available over the counter and can be performed at home. However, a blood test provides more accurate readings but requires a visit to a healthcare provider and a blood draw.

Sources

1. https://diabetes.org/about-diabetes/complications/ketoacidosis-dka/ 

2. https://www.mdpi.com/2072-6643/16/12/1849 

3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6472268/