What Are Ketones? Uses, Limits, Risks, and Testing

ketones

Ketones are ordinary fuel molecules made primarily by the liver when carbohydrate availability is low and fatty-acid delivery is high. They help the body adapt to fasting, prolonged exercise, starvation, and a ketogenic diet. They are not a “superfuel,” and producing more of them is not automatically healthier.

That distinction matters because ketosis appears in several very different contexts: a normal overnight fast, a medically supervised ketogenic diet for epilepsy, and life-threatening diabetic ketoacidosis are not interchangeable.

How the Body Makes and Uses Ketones

The three ketone bodies are acetoacetate, beta-hydroxybutyrate, and acetone. When insulin is relatively low and glucagon is higher, the liver converts fatty acids into ketones. Tissues including the brain can then convert acetoacetate and beta-hydroxybutyrate into energy.¹

Under ordinary fed conditions, the brain relies mainly on glucose. During prolonged fasting or sustained carbohydrate restriction, circulating ketones rise and provide a larger share of its energy. Some glucose is still required and is produced by the liver through gluconeogenesis.

This flexibility is a useful survival adaptation. It does not prove that ketones are the brain’s preferred fuel or that nutritional ketosis is necessary for mental clarity, fat loss, or metabolic health.

When Ketosis Has a Proven Medical Role

The strongest established use is drug-resistant epilepsy, particularly in children. Ketogenic therapies can reduce seizure frequency for some patients, although gastrointestinal effects, difficulty adhering, altered lipids, kidney stones, and nutritional deficiencies require clinical oversight.²

Researchers are also studying ketogenic diets in serious mental illness, neurological disease, and cancer. Those hypotheses are worth testing, but early pilot studies, mechanisms, and case reports do not establish routine treatment. A therapeutic diet should be held to the same evidentiary standard as any other intervention.

For weight loss, ketogenic diets can work quickly. Early scale changes include loss of glycogen and its associated water, followed by fat loss when the diet creates an energy deficit. Reduced food variety and higher protein intake may also suppress appetite. Over longer periods, however, average differences between low-carbohydrate and other calorie-reducing diets tend to narrow as adherence declines.³

The Cardiovascular Tradeoff

Responses vary, but ketogenic diets can raise LDL cholesterol—and sometimes ApoB, the number of atherogenic lipoprotein particles—especially when they contain substantial butter, coconut oil, fatty meat, or other saturated-fat sources.⁴

LDL is not merely an association. Genetic, epidemiological, and randomized evidence supports a causal role for LDL-containing particles in atherosclerotic cardiovascular disease.⁵ Improvements in triglycerides, glucose, or body weight do not cancel the risk implied by a substantial rise in LDL/ApoB.

Someone choosing a ketogenic diet should therefore consider:

• replacing saturated fats with olive oil, canola oil, nuts, seeds, avocado, and fish;
• obtaining a lipid panel and, when appropriate, ApoB before and after the change;
• reconsidering the diet if atherogenic lipoproteins rise substantially; and
• choosing a less restrictive pattern if ketosis is difficult to maintain.

Nutritional Ketosis Is Not Ketoacidosis

In nutritional ketosis, ketones generally remain regulated and blood pH stays normal. Diabetic ketoacidosis (DKA) involves dangerous ketone accumulation, acidosis, and usually severe insulin deficiency. It is an emergency.

People with type 1 diabetes, a history of DKA, pregnancy, eating disorders, pancreatic or liver disease, or certain rare metabolic disorders should not begin a ketogenic diet without qualified medical guidance. SGLT2 diabetes medicines can increase the risk of ketoacidosis even when glucose is not extremely high.

Seek urgent care for symptoms such as persistent vomiting, abdominal pain, deep rapid breathing, confusion, severe dehydration, or fruity-smelling breath—especially with diabetes.

Do You Need to Measure Ketones?

Most people do not.

• Blood beta-hydroxybutyrate meters are the most useful home method when medical monitoring is indicated.
• Urine strips detect acetoacetate but become less informative as the body adapts.
• Breath meters estimate acetone and are less established for clinical decisions.

A ketone number is not a health score. There is no validated “optimal” ketone target for routine weight loss, depression, ADHD, anxiety, cancer prevention, or longevity. The glucose-ketone index is used in some research settings but should not direct cancer treatment or general wellness.

A More Useful Question

Instead of asking whether glucose or ketones are the better fuel, ask whether the dietary pattern is safe, nutritionally adequate, affordable, compatible with your life, and likely to improve the outcomes you care about.

Ketones are a valuable part of human metabolism and a useful medical tool in specific settings. They do not turn a restrictive diet into a universal prescription.