Ketosis vs ketoacidosis · Blood ketones

Ketosis vs Ketoacidosis: What the Numbers Actually Mean

The difference is insulin. Nutritional ketosis runs between about 0.5 and 3 mmol/L of blood ketones with normal blood sugar and pH; ketoacidosis happens when insulin is missing, and ketones can climb as high as 20 mmol/L, usually with high blood sugar.

One is a regulated fuel state your brain uses readily. The other is a medical emergency. They share half a name, and the difference comes down to one hormone and a handful of numbers.

Ketosis vs ketoacidosis is one of the most misunderstood comparisons in everyday medicine, and the mix-up is not harmless. People get warned away from a normal fuel state because it sounds like an emergency, while others on certain diabetes drugs miss a real emergency because their blood sugar looks fine. In the video Your Brain Was Built for Ketones, Not Sugar, Dr. Padda argues that the brain was designed to use ketones well. The numbers below explain what that means for you, and where the line into danger actually sits.

Measura [Cardiometabolic and Autonomic Health Analysis] does not put anyone into ketosis or treat anything. It measures the metabolic terrain that decides how your body handles fuel, and sends those results to your physician.

How does your brain use ketones?

Ketones are made by the liver from fat when carbohydrate is scarce. Unlike glucose, which the brain pulls in according to how busy its neurons are, ketones enter roughly in proportion to how much is in the blood. When nine healthy adults fasted for 3.5 days, both their blood ketones and the flow of ketones into the brain rose more than 10 times.

How much of the brain’s energy that covers depends on the level. At about 1 mmol/L, ketones supply 10–15% of brain energy. After four days on a strict ketogenic diet, an estimated 33%. In three adults studied after 38–41 days of total starvation, 58%. A well-fed brain with trace ketones is running mostly on glucose, and some glucose is always needed. Your liver makes that glucose from protein and the glycerol in fat, which is why carbohydrate, about half of the calories in the American diet at 50.5% in a 2016 survey of U.S. adults, has no established minimum requirement.

What blood ketone level means nutritional ketosis?

Nutritional ketosis starts once blood ketones pass 0.5 mmol/L and usually runs between 0.5 and 3. Blood sugar stays normal. Blood pH stays normal. Insulin is low but present, and it acts like a governor on an engine: it lets the liver make ketones without letting production run away. Ketones even help apply their own brake, through a receptor that slows the release of fat when levels rise.

This is not exotic. Healthy adults reach about 1 mmol/L after prolonged exercise or 24 hours without food, and 76% of breastfed newborns in one study crossed 0.5 mmol/L in their first days. Neurology has used ketogenic diets to treat epilepsy since the 1920s.

What is ketoacidosis, and why is insulin the difference?

Diabetic ketoacidosis happens when insulin is missing or nearly so. With the governor gone, ketones can climb to as high as 20 mmol/L, several times and sometimes more than ten times the levels of nutritional ketosis, usually with high blood sugar and acid building up in the blood. British diabetes guidelines treat ketones above 3.0 mmol/L, together with a pH below 7.3 and low bicarbonate, as the emergency zone. It happens classically in type 1 diabetes and can occur in type 2.

There is one exception every reader should know. A class of diabetes drugs called SGLT2 inhibitors can cause ketoacidosis while blood sugar looks normal. On one of those drugs, or on insulin, a normal glucose reading is not reassurance, and any plan to cut carbohydrate is a conversation to have with your prescribing physician first. Do not start, stop or change a medication on your own.

Ketosis vs ketoacidosis: why do people mix them up?

Two biological facts get blurred: ketones as a regulated fuel, and ketones as a symptom of insulin failure. A third driver is social. For decades the American food supply has delivered carbohydrate at every meal, so most adults rarely experience ketosis after infancy, and clinicians see ketones mainly in emergency rooms. Dr. Padda has his own history here. He spent years as a strict vegetarian defending dietary guidelines he later abandoned when the physiology stopped supporting them.

What can a blood ketone number tell you?

Beta-hydroxybutyrate, the main blood ketone, can be read with a fingerstick meter or ordered by your physician. That is a different test from those in Measura’s library. A single value tells you where you are at that moment; it says nothing about why, and it should always be read next to a glucose value.

The bigger question is whether your body can switch fuels at all. High insulin keeps the liver from making ketones, and insulin can run high for years while glucose stays normal. That is where measurement helps:

• Laboratory panels show the metabolic picture in your blood work, as numbers rather than flags.
• Bioimpedance body composition uses a weak electrical signal to split your weight into its fat and muscle compartments.
• Indirect calorimetry measures the oxygen you use and carbon dioxide you breathe out at rest to calculate your resting metabolic rate, instead of guessing it from a formula. See measured versus estimated metabolic rate.

For the full study-by-study evidence, including the pregnancy and newborn data, read the Chapter 2 companion to The Starved Brain by Dr. Gurpreet Singh Padda, MD, MBA, MHP. Unmeasured is unmanaged, and knowing your own numbers turns a debate about diets into a decision you make with your physician.

Frequently asked questions

Is being in nutritional ketosis dangerous?

For most people it is a regulated state: ketones between 0.5 and 3 mmol/L, with normal blood sugar and pH, and insulin still present to keep production in check. The situations that need a physician first are pregnancy, type 1 diabetes, and treatment with insulin or SGLT2 inhibitors. Learn more about insulin resistance and metabolic health.

What blood ketone level counts as ketoacidosis?

Guidelines place the emergency above 3.0 mmol/L with acidosis, meaning a blood pH below 7.3 and low bicarbonate. In ketoacidosis levels can reach 20 mmol/L. The ketone number alone is not the diagnosis; glucose, pH and symptoms are read together, and anyone unwell with high ketones needs urgent care. See understanding your results.

Can Measura measure my ketones?

A ketone reading usually comes from a fingerstick meter or a lab order from your physician, which is separate from the Measura test library. What Measura shows is the terrain behind it: the metabolic picture in blood work, body composition and resting energy use, reported to your physician. See the laboratory panels page for what that testing covers.

Does my brain need carbohydrate to work?

Your brain always needs some glucose, but your liver can make it from protein and the glycerol in fat. Carbohydrate has no established minimum dietary requirement. When ketones are available, the brain takes them up in proportion to their blood level. The first half of that story, why the brain runs short even in a well-fed body, is what your weight can hide.

Why does insulin matter if my blood sugar is normal?

Insulin decides whether your liver is allowed to make ketones, and it can stay high for years while glucose looks fine because the pancreas is working overtime. A normal sugar reading shows the system is coping, not how hard it is straining. Read what insulin resistance looks like before diabetes.

Can ketosis turn into ketoacidosis?

For most people, no. In nutritional ketosis a small amount of insulin acts like a governor on an engine: the liver makes ketones, but production cannot run away, and ketones help slow their own supply. Ketoacidosis happens when insulin is missing or nearly so, classically in type 1 diabetes. SGLT2 inhibitor drugs are the exception to know, because they can cause ketoacidosis while blood sugar looks normal.

Is having ketones the same as ketoacidosis?

No. Healthy adults reach about 1 mmol/L after long exercise or 24 hours without food, and 76% of breastfed newborns in one study passed 0.5 mmol/L in their first days. Ketones are a regulated fuel your brain takes up readily. Ketoacidosis is ketones plus insulin failure: levels that can climb as high as 20 mmol/L, usually with high blood sugar and acid building up in the blood.

References

• Volek, J. S., Noakes, T., & Phinney, S. D. (2015). Rethinking fat as a fuel for endurance exercise. European Journal of Sport Science, 15(1), 13–20. https://doi.org/10.1080/17461391.2014.959564
• Gershuni, V. M., Yan, S. L., & Medici, V. (2018). Nutritional ketosis for weight management and reversal of metabolic syndrome. Current Nutrition Reports, 7(3), 97–106. https://doi.org/10.1007/s13668-018-0235-0
• Puchalska, P., & Crawford, P. A. (2017). Multi-dimensional roles of ketone bodies in fuel metabolism, signaling, and therapeutics. Cell Metabolism, 25(2), 262–284. https://doi.org/10.1016/j.cmet.2016.12.022
• Mustafa, O. G., Haq, M., Dashora, U., Castro, E., Dhatariya, K. K., & Joint British Diabetes Societies (JBDS) for Inpatient Care Group (2023). Management of Hyperosmolar Hyperglycaemic State (HHS) in adults: An updated guideline from the Joint British Diabetes Societies (JBDS) for Inpatient Care Group. Diabetic Medicine, 40(3), Article e15005. https://doi.org/10.1111/dme.15005
• Dhatariya, K. K., & Joint British Diabetes Societies for Inpatient Care (2022). The management of diabetic ketoacidosis in adults—An updated guideline from the Joint British Diabetes Society for Inpatient Care. Diabetic Medicine, 39(6), Article e14788. https://doi.org/10.1111/dme.14788
• Hasselbalch, S. G., Knudsen, G. M., Jakobsen, J., Hageman, L. P., Holm, S., & Paulson, O. B. (1995). Blood-brain barrier permeability of glucose and ketone bodies during short-term starvation in humans. American Journal of Physiology, 268(6 Pt 1), E1161–E1166. https://doi.org/10.1152/ajpendo.1995.268.6.E1161
• Courchesne-Loyer, A., Croteau, E., Castellano, C.-A., St-Pierre, V., Hennebelle, M., & Cunnane, S. C. (2017). Inverse relationship between brain glucose and ketone metabolism in adults during short-term moderate dietary ketosis: A dual tracer quantitative positron emission tomography study. Journal of Cerebral Blood Flow & Metabolism, 37(7), 2485–2493. https://doi.org/10.1177/0271678X16669366
• Owen, O. E., Morgan, A. P., Kemp, H. G., Sullivan, J. M., Herrera, M. G., & Cahill, G. F., Jr. (1967). Brain metabolism during fasting. Journal of Clinical Investigation, 46(10), 1589–1595. https://doi.org/10.1172/JCI105650
• Shan, Z., Rehm, C. D., Rogers, G., Ruan, M., Wang, D. D., Hu, F. B., Mozaffarian, D., Zhang, F. F., & Bhupathiraju, S. N. (2019). Trends in dietary carbohydrate, protein, and fat intake and diet quality among US adults, 1999–2016. JAMA, 322(12), 1178–1187. https://doi.org/10.1001/jama.2019.13771

Related reading

• Can You Be Overweight and Malnourished? What Your Numbers Show
• Type 3 Diabetes: What a Normal Blood Sugar Test Can Miss
• Laboratory Panels

Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP, medical director of Measura. Last reviewed September 12, 2026.