The ketogenic diet has become increasingly popular as a way to lose weight and improve metabolic health.
In recent years, researchers have also investigated its potential effects on obesity, type 2 diabetes and other medical conditions, including epilepsy.
What Is the Ketogenic Diet?
The ketogenic diet is an eating pattern characterised by a substantial reduction in carbohydrate intake, high fat consumption and adequate, usually moderate, protein intake.
In most versions of the diet, carbohydrates are restricted to approximately 20–50 grams per day, although the exact amount varies depending on the protocol and the individual.
In a typical ketogenic diet, most daily energy intake comes from fat.
The main goal is to achieve a metabolic state known as nutritional ketosis.
The ketogenic diet differs from conventional low-carbohydrate diets because carbohydrate restriction is generally more severe and is specifically intended to increase the production of ketone bodies. [1]
How Does the Ketogenic Diet Work?
To understand how the ketogenic diet works, we first need to look at how the body produces and uses energy.
Glucose is an important energy source for many cells and tissues.
When carbohydrate intake is significantly reduced, the body undergoes several metabolic and hormonal adaptations.
Lower glucose availability and reduced insulin levels encourage the release of stored fatty acids and increase their oxidation.
In the liver, some of these fatty acids are used to produce ketone bodies through a process known as ketogenesis.
The main ketone bodies are acetoacetate, beta-hydroxybutyrate, and acetone.
Acetoacetate and beta-hydroxybutyrate can serve as alternative energy sources for various tissues, including the brain. [1]
What Happens to the Brain During Ketosis?
When carbohydrates are readily available, the brain primarily uses glucose for energy.
However, during prolonged fasting or a ketogenic diet, it can adapt to using ketone bodies.
This adaptation reduces the brain’s glucose requirements but does not eliminate them.
The body continues to produce glucose through a process called gluconeogenesis, using substances such as glycerol, lactate, and certain amino acids.
Therefore, the fact that the brain can use ketone bodies does not mean it no longer needs glucose.
Similarly, the body’s ability to survive on very little dietary carbohydrate does not, in itself, demonstrate that a ketogenic diet is the best choice for long-term health and wellbeing. [1,2]
What Foods Can You Eat on a Ketogenic Diet?
A ketogenic diet typically includes foods that are low in carbohydrates and relatively high in fat.
Common examples include olive oil, nuts, seeds, avocados, fish, eggs, meat, and various non-starchy vegetables.
By contrast, foods such as grains, bread, pasta, rice, potatoes, legumes and many fruits are significantly restricted.
However, not all ketogenic diets are nutritionally equivalent.
A ketogenic diet based mainly on olive oil, fish, nuts and vegetables is considerably different from one that includes large amounts of butter, processed meats and foods high in saturated fat.
Food quality remains important, regardless of how many carbohydrates a diet contains.
What Are the Scientifically Proven Benefits of the Ketogenic Diet?
The effectiveness of the ketogenic diet has been investigated in several clinical settings.
However, the quality and strength of the available evidence vary considerably depending on the condition being studied.
1. Ketogenic Diet and Epilepsy
Epilepsy is one of the most extensively studied clinical applications of the ketogenic diet.
Its therapeutic use dates back to the 1920s and primarily involves people with drug-resistant epilepsy, a condition in which seizures remain inadequately controlled despite appropriate treatment with antiseizure medications.
A Cochrane systematic review published in 2020 included 13 randomised controlled trials involving a total of 932 participants.
The findings suggested that, in children with drug-resistant epilepsy, ketogenic diets may increase the likelihood of achieving a substantial reduction in seizure frequency.
More specifically, children following a ketogenic diet may have been up to six times more likely to experience at least a 50% reduction in seizures compared with those receiving usual care.
However, the certainty of the evidence was rated as low to very low, mainly because of small study sizes and the risk of bias.
Evidence of effectiveness in adults remains more limited. [3]
The ketogenic diet is also a treatment of choice for certain rare metabolic disorders, such as glucose transporter type 1 deficiency syndrome (GLUT1 deficiency syndrome).
In these cases, treatment is provided under the supervision of a specialist medical and dietetic team. [4]
2. Ketogenic Diet and Weight Loss
The ketogenic diet can lead to weight loss, particularly during the first few months.
Initial weight loss may be relatively rapid, partly because glycogen stores are depleted, and the water associated with them is lost.
However, long-term body fat loss depends on several factors, including energy intake, overall eating habits and how consistently someone follows the diet.
Is the Ketogenic Diet More Effective Than Other Diets?
A Cochrane systematic review published in 2022 included 61 randomised controlled trials involving 6,925 participants.
The researchers compared low-carbohydrate diets with diets containing a balanced proportion of carbohydrates.
They found that differences in weight loss were relatively small.
Over one to two years, the average difference in weight loss was less than one kilogram.
However, the review included several types of low-carbohydrate diets rather than ketogenic diets exclusively. [5]
A more recent systematic review and meta-analysis, published in August 2026, examined randomised trials of ketogenic diets in which the prescribed energy intake was similar between groups.
The analysis included six studies involving a total of 259 participants.
On average, ketogenic diets were associated with 1.49 kg greater weight loss compared with higher-carbohydrate diets.
However, the certainty of the evidence was rated as low, and most of the studies were relatively short.
Furthermore, prescribing the same energy intake did not necessarily mean that participants actually consumed the same number of calories. [6]
Overall, the ketogenic diet may be an effective option for weight loss. However, current evidence does not demonstrate a consistent, clinically meaningful long-term advantage over other well-designed dietary approaches.
3. Ketogenic Diet and Type 2 Diabetes
Significantly reducing carbohydrate intake can help limit rises in blood glucose after meals and improve certain metabolic markers.
However, the effectiveness of the ketogenic diet needs to be evaluated against other available dietary approaches.
A systematic review and meta-analysis published in Diabetes, Obesity and Metabolism in 2022 included eight randomised controlled trials involving 606 participants.
The findings suggested that very-low-carbohydrate or ketogenic diets could improve certain metabolic markers.
However, results regarding HbA1c levels at 12 months were inconsistent across studies.
The authors concluded that evidence supporting the superiority of ketogenic diets over other dietary strategies remains limited. [7]
Similarly, the Keto-Med trial, a randomised crossover study published in 2022, compared a well-formulated ketogenic diet with a Mediterranean dietary pattern in 40 people with prediabetes or type 2 diabetes.
After 12 weeks on each diet, there was no statistically significant difference in HbA1c between the two interventions.
The ketogenic diet led to a greater reduction in triglyceride levels but was associated with higher LDL cholesterol levels compared with the Mediterranean diet. [8]
The American Diabetes Association’s 2026 recommendations acknowledge that reducing carbohydrate intake may help improve glycaemic control in some adults with diabetes.
However, they emphasise that no single dietary pattern is suitable for everyone and that very-low-carbohydrate diets require individualisation and appropriate monitoring. [9]
4. Ketogenic Diet and Cardiovascular Health
The effects of the ketogenic diet on cardiovascular health remain an important area of research.
Studies suggest that it can lead to favourable changes in certain markers, but not necessarily in all of them.
A meta-analysis of randomised controlled trials published in Endocrine Practice in 2026 examined the effects of ketogenic diets on blood lipid levels in adults.
The analysis included 62 studies.
Compared with control diets, ketogenic diets were associated, on average, with:
- A reduction in triglycerides of approximately 20 mg/dL.
- An increase in HDL cholesterol of approximately 3.6 mg/dL.
- An increase in LDL cholesterol of approximately 8.5 mg/dL.
These changes do not occur to the same extent in everyone. Results may also be influenced by the composition of the diet, the duration of the intervention and the characteristics of the participants. [10]
A reduction in triglycerides is generally considered a favourable change.
However, an increase in LDL cholesterol should not be dismissed, as increased exposure to atherogenic lipoprotein particles is an established causal factor in atherosclerotic cardiovascular disease.
The quality of dietary fats also matters.
The American Heart Association’s 2026 dietary guidance continues to emphasise replacing foods high in saturated fat with sources of unsaturated fat, alongside adequate consumption of vegetables, fruits and fibre-rich foods. [11]
Therefore, assessing the cardiovascular effects of a ketogenic diet should not be limited to changes in HDL cholesterol or triglycerides.
Furthermore, large, long-term randomised controlled trials demonstrating that ketogenic diets reduce heart attacks, strokes or cardiovascular mortality are still lacking.
5. Are There Benefits for Other Medical Conditions?
The ketogenic diet has also been studied in other conditions, including Alzheimer’s disease, cancer and certain neurological or metabolic disorders.
However, the findings remain less conclusive.
For example, a systematic review and meta-analysis published in 2024 investigated the effects of ketogenic diets in patients with cancer.
The review included eight randomised controlled trials lasting between 4 and 16 weeks.
Although reductions in blood glucose were observed, the researchers did not find consistent, significant benefits in other outcomes, including quality of life.
The authors concluded that the available evidence was insufficient to draw definitive conclusions about the effectiveness of ketogenic dietary interventions in patients with cancer. [12]
Therefore, the ketogenic diet is not a proven cancer treatment and should not replace established cancer therapies.
What Are the Potential Side Effects of the Ketogenic Diet?
Although the ketogenic diet may offer benefits in certain circumstances, it is not without potential side effects.
Short-Term Side Effects
During the first few days, some people may experience fatigue, headaches, dizziness, nausea, constipation, and difficulty concentrating.
These symptoms are often described using the informal term keto flu, which is not a recognised medical diagnosis.
Some of these symptoms may be related to changes in fluid and electrolyte balance, as well as the body’s adaptation to the new dietary pattern.
Potential Risks of Long-Term Use
Following a highly restrictive ketogenic diet for an extended period may present additional challenges.
Reducing the intake of fruits, legumes and whole grains can lead to inadequate consumption of dietary fibre and certain micronutrients if the diet is not carefully planned.
Some individuals may also experience substantial increases in LDL cholesterol.
Patients following therapeutic ketogenic diets for epilepsy have also experienced adverse effects, including kidney stones and problems affecting bone health, which require regular monitoring.
A systematic analysis published in BMC Nutrition in 2026 examined 36 prospective studies reporting adverse effects associated with different ketogenic dietary protocols.
Gastrointestinal problems were the most frequently reported category of adverse effects.
However, the studies varied considerably in terms of participant characteristics, dietary protocols, and how adverse effects were recorded.
As a result, it is not possible to calculate a single risk estimate that applies to everyone following a ketogenic diet. [13]
Who Should Be Particularly Cautious?
The ketogenic diet is not suitable for everyone.
Particular caution is needed for people with diabetes who take insulin or medications that can cause hypoglycaemia.
Strict ketogenic diets should also be avoided by people taking SGLT2 inhibitors because of the increased risk of diabetic ketoacidosis.
The American Diabetes Association’s 2026 guidelines do not recommend very-low-carbohydrate eating patterns during pregnancy or breastfeeding, in children except for specific therapeutic indications, or in people with kidney disease, eating disorders, or an increased risk of developing an eating disorder. [9]
Is the Ketogenic Diet Safe in the Long Term?
There are still significant gaps in the scientific evidence regarding the long-term safety of ketogenic diets.
Many clinical trials are relatively short and focus on intermediate metabolic markers, such as body weight, HbA1c, and blood lipid levels.
By contrast, fewer data are available on the effects of following a ketogenic diet over the long term on cardiovascular events, overall mortality, and other important clinical outcomes.
Furthermore, adherence to highly restrictive dietary patterns often declines over time.
This makes it difficult to assess their true long-term effects.