Slovensky (EUR)
Česky (CZK)
Magyar (HUF)
Slovenščina (EUR)
Deutsch (EUR)10. Ketosis and the Ketogenic Diet: How the Body Uses Fats and Ketones
10 · Ketosis and the Ketogenic Diet: How the Body Uses Fats and Ketones
Ketosis is a metabolic state in which the liver produces more ketone bodies and other tissues use them as a source of energy. It can occur during severe carbohydrate restriction or fasting.
We explain how fats, the liver, mitochondria and ATP production are connected, what clinical studies show, and why higher ketone levels do not automatically mean better health.
What is a ketogenic diet?
A ketogenic diet severely restricts carbohydrates, provides adequate protein and supplies a larger proportion of energy from fat. Not every low-carbohydrate diet leads to ketosis. The body continues to use glucose and does not switch all cells to a single fuel. [1]
How are ketone bodies and energy produced?
Carbohydrate restriction changes the hormonal environment and increases the availability of fatty acids to the liver.
Fatty acids are broken down by beta-oxidation in liver mitochondria. Some of the resulting acetyl-CoA is used to produce ketone bodies.
The heart, muscles and, after adaptation, the brain can use acetoacetate and beta-hydroxybutyrate.
In tissues capable of using ketone bodies, they are converted into acetyl-CoA. The Krebs cycle and oxidative phosphorylation follow.
Ketone bodies also include acetone, much of which is exhaled. It is not an equivalent energy fuel to acetoacetate and beta-hydroxybutyrate. The liver produces ketone bodies but cannot use them for its own energy because it lacks the necessary enzyme, SCOT. [1]
Glucose is still needed. Red blood cells have no mitochondria, so they cannot use ketone bodies. The body can also make glucose through gluconeogenesis. Restricting carbohydrates therefore does not remove glucose from the blood. [1]
Ketosis and ketoacidosis are not the same
| Term | Meaning |
|---|---|
| Nutritional ketosis | Regulated production of ketone bodies when nutrient availability changes; acid–base balance is normally maintained. |
| Diabetic ketoacidosis | A dangerous condition involving insulin deficiency, ketone accumulation and metabolic acidosis. It requires urgent treatment. [2] |
Vomiting, abdominal pain, deep breathing and drowsiness or confusion, particularly in someone with diabetes, may indicate ketoacidosis. If you suspect it, seek emergency help and call your local emergency number. [2]
When taking SGLT2 inhibitors, ketoacidosis can develop even without markedly elevated blood glucose. Combining these medicines with a ketogenic diet poses a particular risk. Do not stop prescribed medicines on your own; discuss dietary changes with your doctor. [3]
What has research in humans shown?
In the randomised Keto-Med trial, people with prediabetes or type 2 diabetes followed both a ketogenic and a Mediterranean diet in sequence. After 12 weeks on each diet, there was no significant difference between them in the primary outcome, HbA1c. The ketogenic diet resulted in lower triglycerides but higher LDL cholesterol and lower fibre intake. [4]
The findings of one short study cannot be applied to everyone or establish long-term disease prevention. An improvement in one marker may be accompanied by a worsening of another.
Ketosis does not guarantee body fat loss. The body can also use fat supplied by food. Ketone levels alone therefore do not show how much body fat a person is losing. Energy intake, food composition and sustainability also matter when assessing a diet.
Medical uses and hypotheses under investigation
NICE recommends considering a ketogenic diet for selected epilepsy syndromes or drug-resistant epilepsy under the guidance of a specialist team. This is individually managed treatment, not a self-directed diet. [5]
Research into tumour metabolism does not justify claims that removing carbohydrates will “starve cancer”. A ketogenic diet is not a proven substitute for cancer treatment. Restricting food during cancer can worsen nutritional status. [6]
Claims about “repairing mitochondria”, extending life or automatically activating autophagy cannot be inferred simply from reaching ketosis. Demonstrating a health benefit requires clinical outcomes, not just a change in a metabolic marker.
What the diet contains also matters
The label “keto” alone says nothing about food quality. Protein, fibre, adequate nutrients and suitable fat sources remain important. WHO recommends favouring unsaturated over saturated fats. [7]
- Protein: for example, fish, eggs, tofu or unsweetened dairy products, according to tolerance.
- Vegetables and fibre: a variety of vegetables, nuts and seeds within the overall eating plan.
- Fats: for example, olive oil, nuts and fish; increasing fat intake is not a goal in itself.
- Assessing outcomes: dietary tolerance, nutritional adequacy and, depending on health status, blood glucose or blood lipids.
Severely restricting carbohydrates while taking diabetes medicines may require a clinician to adjust treatment. During pregnancy or breastfeeding, or with an eating disorder or serious illness, do not start a restrictive diet without an individual assessment. Therapeutic ketogenic diets for children require specialist care.
Frequently asked questions
Is every low-carbohydrate diet ketogenic?
No. Carbohydrate restriction may not be sufficient to induce ketosis, and responses vary between people.
Does the body stop needing glucose in ketosis?
No. Some cells still need it. The body can also make it through gluconeogenesis.
Do higher ketone levels mean greater weight loss?
No. Ketone levels alone do not show body fat loss or overall diet quality.
Is ketosis the same as ketoacidosis?
No. Nutritional ketosis is a regulated metabolic state. Diabetic ketoacidosis is a dangerous condition requiring urgent treatment.
Can a keto diet treat cancer?
It is not a proven substitute for cancer treatment. Dietary changes during treatment should be discussed with the oncology and nutrition teams.
Scientific and clinical sources
- NCBI Bookshelf: Biochemistry, Ketogenesis – ketone body production and utilisation.
- NHS: Diabetic ketoacidosis – symptoms and emergency care.
- Mistry and Eschler, 2020: SGLT2 inhibitors and ketogenic diets – a case series of euglycaemic ketoacidosis.
- Gardner and colleagues, 2022: the Keto-Med trial – a randomised comparison of two dietary patterns.
- NICE NG217: Non-pharmacological treatments – ketogenic diets in epilepsy.
- National Cancer Institute: Popular Diets, Supplements, and Cancer – limitations of the evidence and risks of restrictive diets.
- WHO: Healthy diet – nutrition principles and fat quality.
Educational content: This article explains biological processes and research. It does not replace an individual medical assessment, treatment plan or nutrition plan.
