In recent days, messages have been circulating on social media sharing the supposed benefits of fasting and the ketogenic diet, better known as the keto diet, for cancer patients. Following these publications, at VerificaRTVE we have consulted an oncologist and a doctor who is an expert in Nutrition about this debate that has recently been generated on the networks. The two specialists conclude that There is no scientific evidence that supports the fact that fasting and following a diet of this nature have benefits for cancer patients. We will explain it to you.
“It doesn’t matter that you know that cancer devours glucose, that fasting and a ketogenic diet are vital to combat diseases” because of “the drug business,” we read in a message posted on social network X. Another account explains that “you take away sugar, glucose, fructose, carbohydrates from a cancer cell” and “you starve it.” The post adds that “we already know that cancer cells love glucose and survive in an oxygen-deficient environment. If we want to kill cancer cells, we’ll give them a ketogenic diet.” One user responds that “you can’t generalize” and concludes: “Fasting to ‘prevent cancer’ is great. With cancer, it depends…”
Fasting in cancer patients: is there evidence of its efficacy?
To date, there are no clinical studies demonstrating the benefits of intermittent fasting in cancer patients. The scientific secretary of the Spanish Society of Medical Oncology (I’m here), Isabel Echavarría, explains to VerificaRTVE that “there is a lack of solid data in humans, through randomized studies” that demonstrate the benefits of fasting in these patients. “Although there is preclinical data and plausibility [lógica] biological, this must be confirmed in clinical studies,” says the medical oncologist at the Gregorio Marañón University Hospital in Madrid. In this sense, she states that cancer is “a complex process” and therefore insists that “It is difficult to make a general recommendation for intermittent fasting in cancer patients” since there may be “different factors that make adherence or safety difficult.”
Samara Palma, a doctor specializing in Endocrinology and Nutrition, expresses the same opinion: “The European Society of Clinical Practice Guidelines for 2021 clearly does not recommend dietary restriction” of cancer patients. On this issue, Palma is blunt: “You never subject a person to a therapy if you have not demonstrated that it is clearly beneficial for the patient.”which does not put you at risk and has proven its effectiveness in large clinical trials“.
After conducting a search on specialized portals PubMed y Medline Plus, Palma says that we only found “one very specific article” that addresses the use of “a diet similar to fasting in patients with breast cancer.” According to this expert from the Nutrition area of the Spanish Society of Endocrinology and Nutrition (SEEN), this study refers to “patients with breast cancer in a situation of neoadjuvantwhich is the chemotherapy we give them before surgery, at a specific tumor stage.” However, Palma insists: “I wouldn’t even dare to extrapolate the results of this study to all patients with breast cancer.”
What risks can this practice entail for cancer patients?
One in five deaths in cancer patients is caused by malnutrition. “We cannot forget that there is a significant percentage of deaths in cancer patients that is attributed solely and exclusively to the severity of their nutrition,” explains Palma. This doctor from the Nutrition area of the SEEN states that this malnutrition occurs because “The patient is unable to eat as much as he should”“. For this reason, he highlights that “most of the time we are forced to increase their intake with medical-nutritional treatments.”
In an interview in February 2024 in RNE, Nutritionist Julio Basulto explained that a cancer patient could worsen his illness if he fasts. “Fasting a person who has cancer, knowing that so many people with cancer die from weight loss, It is reckless because it can lead to even more weight loss. and thus worsen not only their quality, but their life expectancy.” Basulto also recalled that there are cancer patients who die from caquexiawhich is the loss of body weight and muscle mass caused by cancer or its treatment.
Isabel Echavarría stresses the importance of Study each cancer patient individually since there are many factors involved such as “the age of the patient, baseline nutritional status, type of tumor, type of treatment, toxicities resulting from the treatment,” among others. Therefore, the medical oncologist points out that the practice of fasting in some patients “at risk of malnutrition, or with digestive toxicities such as nausea, vomiting or diarrhea, can be associated with a risk of dehydration or risk of malnutrition with greater fatigue or weight loss.” In addition, she insists that carrying out this practice “can cause distress [estrés negativo] additional in patients already symptomatic due to their disease or treatments“.
What is the ketogenic diet and what is its role in cancer patients?
The ketogenic dietbetter known as the keto diet, is a diet “high in fat, moderate in protein, and low in carbohydrates,” explains Dr. Echevarría. According to this oncologist, it is associated with “weight loss, reduction in inflammation and insulin levels.” However, she is blunt when referring to fasting and the ketogenic diet: “They are not a cure for cancer“. On this point, he highlights that “Such simplistic statements are unrealistic and can have harmful effects on patients.“. He stresses that if “a ketogenic diet killed cancer cells, there would be almost 10 million cancer deaths a year worldwide and more than 114,000 in Spain in 2022.”
Regarding the use of this diet in cancer patients, Echevarría states that “there are preclinical studies in mice” that suggest a benefit “in some specific tumors.” This is the case of “a subtype of breast cancer with a specific mutation or brain tumors,” she explains. However, this expert clarifies that “We do not have robust data in humans and therefore it cannot be routinely recommended.”“. On this point, she insists that the value of this diet “must be confirmed in large, randomized studies” and compared with “other dietary patterns that have been shown to be beneficial, such as the Mediterranean diet or diets enriched with fruits, vegetables and legumes.” Samara Palma explains that, after conducting a search on the keto diet on specialized portals, “we found three systematic reviews in which all three conclude that We do not have unequivocal evidence that it has given us the same result in different types of cancer.”
Nutrition and cancer: two linked concepts
In Spain it is estimated that in 2024 the number of diagnosed cancers will reach 288,664 casesaccording to the calculations of the Spanish Network of Cancer Registries. For this reason, the prevention of the disease plays a very important role. The two experts consulted agree that A healthy diet is a key factor in reducing the risk of cancer and improve the prognosis.
“Obesity is a risk factor for the development of cancer and, therefore, its control is associated with a reduction in the risk of cancer or tumor relapses,” says the medical oncologist at the Gregorio Marañón University Hospital in Madrid. Samara Palma agrees with this argument: “It is true that There is a large burden of cardiovascular disease and tumor diseases that could be attributed to poor lifestyle habits.The nutrition expert says that during consultations she tries to make the diet of patients with cancer “healthier.” “We rely mainly on healthy fats, olive oil, avocado, roasted or natural nuts, and choosing carbohydrates carefully,” concludes Palma.
