Quick answer: Ketosis is a natural metabolic state in which the body uses ketones from fat as its main fuel instead of glucose. It happens when carbohydrate intake is very low: glycogen stores empty, insulin falls, fat is broken down, and the liver makes ketones that cells use for energy. Eating more carbs switches the body back to glucose.
Key takeaways
Ketosis happens when carbohydrates are limited, glycogen runs low and the liver begins turning fat into ketones.
A higher-carbohydrate meal shifts the body back to glucose, and it can take a few days to return to ketosis.
Ketosis is not ketoacidosis, and anyone with diabetes needs medical supervision before trying keto.
How ketosis happens
Limited carbohydrate
Net carbs are kept very low. See carbohydrate intake.
Glycogen depletion
The liver and muscles use up stored glucose (glycogen) over a few days.
Fat breakdown
With insulin lower, fat cells release fatty acids.
Ketone production
The liver turns fatty acids into acetoacetate, beta-hydroxybutyrate and acetone.
Ketone use
Cells, including the brain, convert ketones into energy (ATP).
Maintaining ketosis
Keep carbs low and fat adequate. A higher-carb meal shifts the body back to glucose, and it can take a few days to return to ketosis. Learn how to monitor your ketones and spot signs of ketosis.
Ketosis is not ketoacidosis
Diabetic ketoacidosis is a dangerous condition with very high ketones and blood sugar. If you have diabetes, keto needs medical supervision.
Healthy aging lens
Switching between burning glucose and fat, called metabolic flexibility, is a feature of healthy metabolism. See metabolism and longevity.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you have diabetes or take insulin, sulfonylureas or SGLT2 inhibitors (risk of low blood sugar or ketoacidosis), or if you take blood pressure medication or diuretics. The same is true if you have kidney, liver, gallbladder or pancreas disease, or high cholesterol, if you are pregnant, breastfeeding, or have a history of disordered eating, or if you want a keto plan tailored to your labs and goals.
See a medical provider promptly for nausea and vomiting, abdominal pain, confusion, fruity-smelling breath with rapid breathing, or very high blood sugar or ketone readings, which can signal ketoacidosis.
Want a keto plan that’s safe for your health?
A free 15-minute consultation with Dr. Kneessi. No cost, no obligation. In-office in Odenton, MD or by telehealth.
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Is it safe for me to aim for ketosis, and how would we monitor it?
Could any of my current medications or supplements interact with the options discussed here?
Would any lab testing add useful information in my situation, or is it reasonable to start with daily habits?
Which one or two changes would be most worthwhile for me to focus on first?
Frequently asked questions
What is ketosis?
A metabolic state in which the body burns ketones from fat for fuel.
How do I know I’m in ketosis?
Blood, breath or urine ketone tests, plus common signs.
How long does it take?
Usually a few days, but it varies.
Is ketosis dangerous?
Nutritional ketosis is generally safe for healthy adults; ketoacidosis is an emergency.
Sources
- Laffel L. Ketone bodies: a review of physiology, pathophysiology and application of monitoring to diabetes. Diabetes Metab Res Rev 1999. PMID: 10634967. https://pubmed.ncbi.nlm.nih.gov/10634967/
- Owen OE, et al. Brain metabolism during fasting. J Clin Invest 1967. PMID: 6061736. https://pmc.ncbi.nlm.nih.gov/articles/PMC292907/
- Dhatariya KK, et al. Diabetic ketoacidosis. Nat Rev Dis Primers 2020. PMID: 32409703. https://pubmed.ncbi.nlm.nih.gov/32409703/
- Goodpaster BH, Sparks LM. Metabolic Flexibility in Health and Disease. Cell Metab 2017. PMID: 28467922. https://pmc.ncbi.nlm.nih.gov/articles/PMC5513193/
- MedlinePlus: Ketones in Blood
- MedlinePlus: Diabetic Ketoacidosis
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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