The ketogenic diet can help some people lose weight in the short term, but reaching ketosis does not by itself show that a diet is healthy or that it will produce better long-term results.
A ketogenic diet is a very low-carbohydrate, high-fat eating pattern. Many versions limit carbohydrates to fewer than 50 grams a day, with some going as low as 20 grams. Fat generally provides most of the diet’s calories, while protein is consumed in moderate amounts.
When carbohydrate intake falls sharply, the body has less glucose available for energy and begins breaking down fat. The liver produces ketones, which can be used as an alternative fuel. This metabolic state is known as nutritional ketosis.
What the evidence shows
Studies suggest ketogenic and other very-low-carbohydrate diets can produce greater weight loss in the short term than some low-fat diets. The difference tends to become smaller over longer periods, however, and maintaining any weight loss depends on whether a person can sustain the eating pattern.
Some people also report feeling fuller when eating diets higher in protein and fat. That may reduce food intake and contribute to weight loss. But ketosis itself is not a guarantee of fat loss, and the overall amount of food consumed remains important.
Research has also found short-term changes in measures such as blood triglycerides, blood pressure and blood sugar among some people following low-carbohydrate diets. At the same time, LDL cholesterol can increase, particularly when the diet relies heavily on saturated fat.
For that reason, the type of fat matters. Foods such as olive oil, nuts, seeds, avocado and oily fish provide unsaturated fats, while diets high in saturated and trans fats can have less favourable effects on cholesterol and cardiovascular health.
Not everyone responds the same way
The transition to a very low-carbohydrate diet can cause headaches, fatigue, constipation, muscle cramps and other short-term symptoms. Restricting large groups of foods can also make it harder to obtain enough fibre, vitamins and minerals unless the diet is carefully planned.
Long-term evidence on ketogenic diets remains more limited than evidence for many conventional dietary patterns. Harvard’s review of the research notes concerns about nutrient deficiencies and possible longer-term effects, including kidney stones and changes in uric acid levels.
A ketogenic diet is also different from simply eating fewer carbohydrates. A person can reduce refined carbohydrates and added sugars without eliminating nutritious sources such as whole grains, legumes and fruit.
How ketosis can be measured
Ketosis can be assessed through blood, urine or breath testing, but the methods do not provide identical information.
Blood tests measure circulating beta-hydroxybutyrate and provide a current measurement of blood ketones. Urine strips detect ketones that have been excreted in urine, meaning they do not provide the same real-time measurement. Breath devices measure acetone, another type of ketone, but their accuracy and usefulness vary.
The idea that a particular ketone reading, such as 2 or 3 mmol/L, is automatically the ideal target for weight loss is not supported by the evidence. Ketone levels vary according to the individual and the circumstances, and higher ketone levels are not necessarily better.
Ketosis should also not be confused with diabetic ketoacidosis, a potentially dangerous medical condition. In diabetic ketoacidosis, high ketones occur alongside abnormal blood glucose and metabolic acidosis. The 2024 international consensus on diabetic emergencies recommends direct measurement of blood beta-hydroxybutyrate when available for assessing ketoacidosis.
What about cognitive benefits?
There has been research into ketogenic diets for neurological conditions, particularly epilepsy, where medically supervised ketogenic diets have an established therapeutic role.
Research into whether ketogenic diets improve cognitive performance in otherwise healthy people is less conclusive. Claims that ketosis can prevent or treat conditions such as Alzheimer’s or Parkinson’s disease go beyond what current evidence establishes.
The same caution applies to claims that ketogenic diets prevent fatty liver disease or universally improve cholesterol. Health outcomes depend on the person’s overall diet, medical condition and the types of foods used to replace carbohydrates.
The bottom line
A ketogenic diet can be effective for short-term weight loss for some people, but it is not a universally superior diet and reaching ketosis is not, on its own, a measure of health.
For anyone considering a major change to their diet, particularly people with diabetes, kidney disease, heart disease or other medical conditions, medical advice is appropriate before starting. Mayo Clinic also recommends discussing low-carbohydrate diets with a health professional when underlying medical conditions are present.
The strongest evidence supports focusing less on achieving a particular ketone number and more on the overall quality, nutritional adequacy and sustainability of the eating pattern.
