Ketones are molecules your liver produces when your body burns fat for fuel instead of sugar. In small amounts, they’re a normal and even helpful energy source. They become dangerous when they build up faster than your body can use them, turning your blood acidic, a condition that can be life-threatening without treatment.
What Ketones Actually Are
Your body’s preferred fuel is glucose, the sugar that comes from carbohydrates. But when glucose is scarce or your cells can’t access it, your liver breaks down fat and converts it into ketone bodies as a backup fuel. There are two main ketone bodies your liver produces. A third, acetone, is mostly a waste product that gets exhaled through your lungs (which is why people in heavy ketosis sometimes have a distinctive smell on their breath).
This process happens to some degree all the time, even when you’re healthy. It ramps up during fasting, intense exercise, pregnancy, and low-carb diets. The ketones travel through your bloodstream to organs that need energy, where they’re broken down and used. Interestingly, the liver itself can’t use the ketones it makes. It produces them exclusively for other organs to consume.
Why Your Body Actually Needs Them
Ketones aren’t inherently bad. They’re a critical backup fuel, especially for two organs: your brain and your heart. Your brain can’t burn fat directly, so during periods without food, ketones become one of its primary energy sources. Your heart has a particularly high capacity to burn ketones, and research published in Circulation Research describes them as a “critical cardiac fuel” with roles beyond simple energy production, including regulating inflammation and cellular communication.
In heart failure, when the heart loses its ability to efficiently use its usual fuels (fatty acids and glucose), ketone burning increases as a compensatory response. Multiple lines of evidence suggest this shift is adaptive, essentially the heart leaning on ketones to keep up with energy demands when other fuel pathways falter. Researchers are now investigating whether boosting ketone delivery to the heart could have therapeutic value.
During normal fasting or a ketogenic diet, blood ketone levels rise to roughly 1 mmol/L or higher. At these levels, your muscles, brain, and heart oxidize ketones in proportion to how much is available. This is nutritional ketosis, and for most people it’s a manageable metabolic state, not a medical emergency.
When Ketones Turn Dangerous
The danger starts when ketone production spirals out of control and overwhelms your body’s ability to use them. Ketone bodies are acidic. When they accumulate in the blood faster than tissues can burn them, blood pH drops. This is called metabolic acidosis, and in the context of diabetes it’s known as diabetic ketoacidosis, or DKA.
The most common trigger is type 1 diabetes, where the body produces little or no insulin. Without insulin, cells can’t absorb glucose from the bloodstream, so the liver keeps producing ketones at an accelerating rate, even though blood sugar may already be extremely high. It’s a paradox: glucose is flooding the blood, but cells are starving, so the liver acts as though the body is in a famine and churns out more and more ketones.
DKA can also occur in type 2 diabetes during illness, infection, or missed medication. Hospital admissions for DKA have increased substantially over the past decade, according to data tracking hyperglycemic emergencies from 2011 to 2020.
DKA Isn’t the Only Cause
Diabetes gets the most attention, but dangerous ketone buildup can happen in other situations. Alcoholic ketoacidosis occurs in people with chronic alcohol use who are malnourished. Heavy drinking suppresses glucose production while poor nutrition leaves the body with almost no carbohydrate stores. The liver responds by ramping up ketone production, sometimes to dangerous levels. A study of 74 patients with this condition found it often comes layered with other problems: dehydration, alcohol withdrawal, infection, and liver disease, all compounding the acid-base imbalance.
Prolonged starvation triggers a similar mechanism. Without any carbohydrate intake, the body relies entirely on fat breakdown, and ketone production increases dramatically. In most people, the body eventually adapts and stabilizes ketone levels during extended fasting, but in vulnerable individuals, particularly those who are already ill, the system can tip into crisis.
Symptoms to Recognize
DKA typically announces itself in stages. Early symptoms are easy to dismiss: extreme thirst and urinating far more than usual. These happen because your kidneys are working overtime trying to flush excess glucose and ketones from your blood.
If ketones keep rising, more severe symptoms appear quickly:
- Fast, deep breathing (your body’s attempt to blow off acid through your lungs)
- Fruity-smelling breath from exhaled acetone
- Nausea, vomiting, and stomach pain
- Dry skin and mouth
- Flushed face
- Muscle stiffness or aches
- Extreme fatigue
- Headache
The rapid, deep breathing pattern is one of the most distinctive signs. It looks different from normal shortness of breath. The body is essentially hyperventilating in a controlled way to expel carbon dioxide and compensate for the acid flooding the bloodstream.
Blood Ketone Levels and What They Mean
If you have diabetes, blood ketone testing gives you a clear picture of your risk. Cleveland Clinic provides these general ranges:
- Below 0.6 mmol/L: Normal. No concern.
- 0.6 to 1.5 mmol/L: Low to moderate DKA risk. Worth monitoring closely.
- 1.6 to 2.9 mmol/L: High DKA risk. Action needed.
- Above 3.0 mmol/L: Very high DKA risk. This is emergency territory.
Blood ketone meters measure the primary ketone body that circulates during DKA, giving a real-time snapshot of what’s happening. Urine ketone strips are cheaper and more widely available, but they detect a different ketone body and reflect what was in your blood hours earlier, not right now. For people actively managing diabetes during illness or high blood sugar, blood testing is the more reliable choice.
What Happens During Treatment
DKA is treated as a medical emergency. The core goals are straightforward: rehydrate the body, bring insulin levels back up so cells can absorb glucose again, and correct the electrolyte imbalances that develop as the crisis unfolds.
Fluids come first, often rapidly, to counteract the severe dehydration that comes from excessive urination. Insulin is given through an IV at a continuous, carefully controlled rate to gradually bring blood sugar down and stop the flood of ketone production. The emphasis is on “gradually” because dropping blood sugar too fast carries its own risks.
One of the less obvious dangers of DKA is what it does to your electrolytes, particularly potassium. Insulin normally helps move potassium into cells, and when insulin has been absent, potassium levels in the blood can look normal or even high, masking the fact that total body stores are depleted. As insulin therapy begins and potassium shifts back into cells, blood levels can plummet dangerously. This is why potassium replacement is a central part of DKA treatment, monitored closely with frequent blood draws.
Most people recover from DKA within 24 to 48 hours with proper hospital care. The transition back to normal insulin happens once acid levels in the blood normalize and ketones drop back below about 1 mmol/L.
The Bottom Line on “Dangerous”
Ketones sit on a spectrum. At low levels, they’re a useful fuel your body has relied on throughout human evolution, powering your brain during fasts and supporting your heart under stress. At high levels, they turn your blood into an acidic environment that disrupts virtually every system in your body. The difference between helpful and harmful comes down to how fast they’re produced, whether your body can keep up with clearing them, and whether insulin is present to regulate the whole process. For people with diabetes, this makes ketone awareness not just useful but essential.