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title: "Ketosis Definition & Meaning | infoMD Health Glossary"
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# Ketosis

ke·to·sis - kee-TOH-sis

## Definition

Ketosis is a metabolic state in which the body shifts from using glucose as its primary fuel source to burning fat and producing molecules called ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone) for energy. This shift occurs when carbohydrate intake is significantly reduced - typically below 20-50 grams per day - depleting the body's glycogen stores and forcing it to mobilize fatty acids from stored body fat and dietary fat.

Ketosis is a normal physiological response that historically allowed humans to survive periods of food scarcity. When glucose is unavailable, the liver converts fatty acids into ketone bodies, which can cross the [blood-brain barrier](/glossary/blood-brain-barrier) and fuel the brain, heart, kidneys, and muscles. The brain typically relies on glucose but can adapt to derive up to 75% of its energy from ketones during extended ketosis.

Nutritional ketosis (blood ketone levels of 0.5-3.0 mmol/L) is a controlled, safe metabolic state distinct from diabetic ketoacidosis (DKA), a dangerous condition in type 1 diabetes where ketone levels spike to 10+ mmol/L alongside very high blood glucose. The [ketogenic diet](/glossary/ketogenic-diet) deliberately induces nutritional ketosis and has been studied for weight loss, [type 2 diabetes](/conditions/type-2-diabetes) management, [epilepsy](/conditions/epilepsy) treatment (its original medical use), and neurological conditions.

## Also Known As

Nutritional ketosis Dietary ketosis 

## Key Facts

-   • Nutritional ketosis typically requires restricting carbohydrates to 20-50 grams per day. 
-   • The ketogenic diet was originally developed in the 1920s as a treatment for drug-resistant epilepsy in children. 
-   • Ketone bodies can fuel the brain when glucose is scarce - the brain can adapt to derive up to 75% of energy from ketones. 
-   • Common signs of entering ketosis include reduced appetite, increased thirst, fruity breath odor, and temporary fatigue ('keto flu'). 
-   • Nutritional ketosis (0.5-3.0 mmol/L ketones) is physiologically distinct from dangerous diabetic ketoacidosis (10+ mmol/L). 

## How It Relates To Your Health

Ketosis has gained significant attention for potential benefits in weight management, blood sugar control, and neurological health. If you're considering a [ketogenic diet](/glossary/ketogenic-diet), discuss it with your healthcare provider - particularly if you have diabetes, kidney disease, liver disease, or a history of disordered eating.

Research supports the ketogenic diet's efficacy for drug-resistant epilepsy and shows promising results for [type 2 diabetes](/conditions/type-2-diabetes) management and short-term weight loss. However, long-term safety data is limited, and the diet's restrictive nature can make it difficult to sustain and may lead to nutritional deficiencies if not carefully planned.

## Related Terms

[Ketogenic Diet](/glossary/ketogenic-diet)[Metabolism](/glossary/metabolism)[Blood Glucose](/glossary/blood-glucose)[Insulin](/glossary/insulin)[Triglycerides](/glossary/triglycerides)[Macronutrients](/glossary/macronutrients)

## Related Articles

[![Intermittent Fasting: What the Science Actually Says](https://images.unsplash.com/photo-1504674900247-0877df9cc836?w=1200&h=630&fit=crop&fm=webp)](/nutrition/intermittent-fasting-science)

[](/nutrition/intermittent-fasting-science)[Nutrition & Diet](/nutrition)

### Intermittent Fasting: What the Science Actually Says

2025-09-01

## Sources

1.  [Ketosis](https://my.clevelandclinic.org/health/articles/ketosis) - Cleveland Clinic
2.  [Ketogenic Diet](https://www.ncbi.nlm.nih.gov/books/NBK499830/) - StatPearls / PubMed
3.  [Diet Review: Ketogenic Diet](https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/ketogenic-diet/) - Harvard T.H. Chan School of Public Health

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[Amino Acid](/glossary/amino-acid)[Electrolytes](/glossary/electrolytes)[Enzyme](/glossary/enzyme)[Glycemic Index](/glossary/glycemic-index)[Ketogenic Diet](/glossary/ketogenic-diet)[Lipids](/glossary/lipids)

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