Why Is the Ketogenic Diet Being Studied in Cancer?
In recent years, the ketogenic diet has attracted growing interest from researchers investigating potential approaches to cancer treatment.
This interest is largely related to how cancer cells obtain and use energy.
Many cancer cells take up large amounts of glucose and rely on glycolysis to meet some of their energy needs. This characteristic is associated with what is known as the Warburg effect.
The ketogenic diet substantially restricts carbohydrate intake, leading the body to increase its production of ketone bodies.
Researchers are therefore investigating whether these metabolic changes could influence the growth of certain tumours or improve the effectiveness of conventional cancer treatments.
However, cancer cells do not rely exclusively on glucose. Many tumours can use different energy sources, and the body continues to produce glucose even when carbohydrate intake is severely restricted.
This is explored in more detail in our article Sugar and Cancer: What Does the Scientific Evidence Say?
A diet may alter the body’s metabolism, but this does not necessarily mean it will have a meaningful effect on cancerous tumours.
What Do Clinical Studies Actually Show?
Much of the research investigating the ketogenic diet and cancer survival has focused on glioblastoma, a particularly aggressive malignant brain tumour.
Some of the findings appear striking.
In 2025, for example, a small clinical study involving 18 patients with glioblastoma was published.
The researchers reported that, among the six patients who maintained a ketogenic diet for more than six months, four were recorded as having survived for three years.
By contrast, only one of the twelve patients who did not maintain the diet for the same length of time reached three-year survival.
The authors reported three-year survival rates of 66.7% versus 8.3%, respectively. [2]
But does this prove that the ketogenic diet increased survival?
No. The reason lies in how the study was designed and analysed. In other words, its methodology.
First, the study included only 18 patients and had no randomised control group.
Patients were divided into groups according to how long they managed to follow the diet.
This creates an important problem. Patients who were in better overall health or whose disease progressed more slowly may have found it easier to maintain the diet for longer.
Furthermore, to be included in the group that maintained the diet, patients had to remain on the dietary intervention for more than six months.
This introduces a risk of a specific form of time-related bias known as immortal time bias.
There were also differences in the cancer treatments participants received, while one of the six patients in the high-adherence group had not yet completed three years of follow-up.
Therefore, we cannot determine whether the difference in survival was caused by the ketogenic diet or by other factors.
Similar questions arise from other studies.
Another small clinical trial published in 2025, involving 17 patients with glioblastoma, reported a median survival of 29.4 months from the start of the ketogenic diet.
Participants continued to receive conventional cancer treatments alongside the dietary intervention. [3]
The findings were described as encouraging. However, the study had no control group, making it impossible to determine the independent effect of the diet.
More recently, in June 2026, a study was published involving 18 patients who followed a programme combining a ketogenic diet with time-restricted eating (fasting), alongside standard cancer treatment.
Median overall survival was 21.5 months, compared with 14.7 months in a non-randomised comparison group. [4]
Although the difference was statistically significant in the initial analysis, the lack of randomisation and the combination of several interventions mean that the results cannot be attributed solely to the ketogenic diet.
By contrast, a randomised clinical trial involving 50 patients with recurrent malignant gliomas found that combining a short-term ketogenic diet and fasting with radiotherapy did not lead to a statistically significant improvement in overall survival or progression-free survival compared with the control group. [5]
However, the intervention was relatively short, so these findings do not rule out the possibility that different dietary protocols could produce different effects.
What Can We Conclude from the Available Research?
To better understand the strength of the evidence, we also need to examine systematic reviews, which assess findings from multiple studies.
Several such reviews were published in 2026, examining the use of ketogenic diets in patients with glioblastoma and other malignant brain tumours.
Some researchers described the findings as encouraging, noting that certain groups of patients appeared to survive longer than patients included in earlier studies. [6]
However, comparing patients with those from historical studies does not, on its own, demonstrate that a treatment is effective.
There may be important differences in the treatments received, patient characteristics, and underlying prognosis.
Other systematic reviews published in 2026 highlighted the limitations of the existing evidence.
One review included 23 studies involving a total of 306 patients and identified substantial differences in study methods, dietary interventions and reported outcomes.
The randomised trials had not demonstrated a statistically significant improvement in survival. [7]
Another review, published in September 2026, concluded that the available clinical evidence primarily supports the feasibility of ketogenic dietary interventions and their metabolic effects, without establishing an independent survival benefit. [8]
It is also important to recognise that most clinical research has focused on brain tumours.
These findings cannot automatically be generalised to all types of cancer.
What Do Scientific Organisations Recommend?
The American Society of Clinical Oncology (ASCO) states that the available evidence is insufficient to support a recommendation either for or against the ketogenic diet as a means of improving cancer treatment outcomes. [9]
The European Society for Clinical Nutrition and Metabolism (ESPEN) also emphasises the importance of adequate nutritional support for people undergoing cancer treatment.
Unintentional weight loss, reduced food intake and malnutrition are significant concerns during cancer treatment.
For this reason, restrictive diets without proven clinical benefits should be approached with particular caution. [10]
Conclusion
Based on the scientific evidence available up to October 2026, there is insufficient evidence to conclude that the ketogenic diet improves survival in patients with cancer.
Larger, well-designed randomised controlled trials are needed to establish whether the ketogenic diet offers any meaningful benefit as a complementary intervention.