Ketogenic diets are high in fat, moderate in protein, and low in carbohydrates, with weak to preliminary evidence of anticancer effects. A ketogenic diet can also improve body weight and insulin resistancea condition in which cells in your muscles, fat, and liver don’t respond well to insulin and can’t efficiently take up glucose from your blood for energy and support healthier blood sugar levels.
Safety and precautions
Cancer mortality or metastases
A very large combined analysis of 10 studies found higher cancer-related mortality among people eating low-carbohydrate diets as a whole or animal-based low carbohydrate diets, but not plant-based low-carbohydrate diets.1Ghorbani Z, Kazemi A et al. Overall, plant-based, or animal-based low carbohydrate diets and all-cause and cause-specific mortality: a systematic review and dose-response meta-analysis of prospective cohort studies. Ageing Research Reviews. 2023 Sep;90:101997.
Also see preclinical (animal) evidence that a ketogenic diet increases breast tumor metastases in Are you a health professional? ›
Side effects and adverse events
A ketogenic diet (KD) is a complex diet to follow and may cause side effects, some of which may be serious: loss of appetite,2Schmidt M, Pfetzer N, Schwab M, Strauss I, Kammerer U. Effects of a ketogenic diet on the quality of life in 16 patients with advanced cancer: a pilot trial. Nutrition & Metabolism. 2011 July 27;8(1):54. weight loss, nutrient deficiencies, and more. Unless weight loss is desirable, this could be a concern. “As cancer patients are particularly susceptible to clinically significant malnutrition in the form of weight loss from both fat and muscle mass, this side effect should be most carefully evaluated before applying the diet in clinical settings.”3Erickson N, Boscheri A, Linke B, Huebner J. Systematic review: isocaloric ketogenic dietary regimes for cancer patients. Medical Oncology. 2017 May;34(5):72. Individualized close monitoring of the diet and ongoing education and support is recommended to improve safety and enhance completion of the KD.4Karen Collins, MS, RDN, CDN, FAND, Oncology Dietitian and Nutrition Advisor to the American Institute for Cancer Research. Presentation March 2017: “Culinary Translation in Breast Cancer Care and Survivorship” in Washington, DC; Erickson N, Boscheri A, Linke B, Huebner J. Systematic review: isocaloric ketogenic dietary regimes for cancer patients. Medical Oncology. 2017 May;34(5):72; Oliveira CL, Mattingly S, Schirrmacher R, Sawyer MB, Fine EJ, Prado CM. A nutritional perspective of ketogenic diet in cancer: a narrative review. Journal of the Academy of Nutrition and Dietetics. 2017 Mar 30. pii: S2212-2672(17)30115-6; Winters N, Kelley JH. The Metabolic Approach to Cancer: Integrating Deep Nutrition, the Ketogenic Diet, and Nontoxic Bio-Individualized Therapies. Vermont: Chelsea Green Publishing. 2017; Lise Alschuler, email communications, September 18, 2017 and October 24, 25, 26, 2017.
Also, because any anticancer effects of a ketogenic diet are due to metabolic changes, we highly recommend you be carefully assessed by a qualified physician or practitioner to determine the specific manipulation that might work best in relation to the metabolic characteristics of your cancer.
Preliminary evidence of low adherence and completion rates among people following a ketogenic diet; researchers interpret these as an indication that side effects or quality of life during KD are a barrier to participation or adherence
- Low rate of acceptance of the KD dietary restrictions by people with cancer—only 37% of those on the KD were able to follow the diet for the duration of the study—in a review of clinical studies5Erickson N, Boscheri A, Linke B, Huebner J. Systematic review: isocaloric ketogenic dietary regimes for cancer patients. Medical Oncology. 2017 May;34(5):72.
- Quality of life was a factor in decisions to decline participation in a trial which also had poor retention—only 4 of 12 patients completed the 3-month diet—among people with glioblastoma in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects6Martin-McGill KJ, Marson AG et al. Ketogenic diets as an adjuvant therapy for glioblastoma (KEATING): a randomized, mixed methods, feasibility study. Journal of Neuro-oncology. 2020 Mar;147(1):213-227.
- People with advanced metastatic tumors and no conventional therapeutic options eating a ketogenic diet showed slightly worse physical function and a weak trend toward lower appetite, but only 5 of 16 people were able to complete the 3-month intervention in a small uncontrolled studya study in which a therapy is used, but without a comparison group against which to judge outcomes; an uncontrolled trial is considered a weak study design.7Schmidt M, Pfetzer N, Schwab M, Strauss I, Kammerer U. Effects of a ketogenic diet on the quality of life in 16 patients with advanced cancer: a pilot trial. Nutrition & Metabolism. 2011 July 27;8(1):54. Our note: the patients in this study were very ill from cancer, and 2 died during the study; symptoms such as these would likely have worsened either with or without the change in diet, but since the study was uncontrolled, we have no comparison group.
Other small studies found that a ketogenic diet was reasonably well tolerated as shown by compliance rates of 50% or higher.8Dardis C, Renda L et al. ACTR-15. Therapeutic ketogenic diet (KD) with radiation and chemotherapy for newly diagnosed glioblastoma—preliminary results from NCT02046187. Neuro-Oncology. 2017 Nov;19(suppl_6):vi4; Santos JG, Da Cruz WMS et al. Efficacy of a ketogenic diet with concomitant intranasal perillyl alcohol as a novel strategy for the therapy of recurrent glioblastoma. Oncology Letters. 2018 Jan;15(1):1263-1270.
Common side effects
People beginning a ketogenic diet sometimes report these side effects. They are usually transient and easily managed:9Branco AF, Ferreira A et al. Ketogenic diets: from cancer to mitochondrial diseases and beyond. European Journal of Clinical Investigation. 2016 Mar;46(3):285-98; Schmidt M, Pfetzer N, Schwab M, Strauss I, Kammerer U. Effects of a ketogenic diet on the quality of life in 16 patients with advanced cancer: a pilot trial. Nutrition & Metabolism. 2011 July 27;8(1):54; Sharifi M, Saber A et al. The effects of portfolio moderate-carbohydrate and ketogenic diets on anthropometric indices, metabolic status, and hormonal levels in overweight or obese women with polycystic ovary syndrome: a randomized controlled trial. Nutrition Journal. 2024 Dec 2;23(1):152.
- Nausea and vomiting (most common); for some people with advanced cancer, nausea and vomiting may worsen over time10Schmidt M, Pfetzer N, Schwab M, Strauss I, Kammerer U. Effects of a ketogenic diet on the quality of life in 16 patients with advanced cancer: a pilot trial. Nutrition & Metabolism. 2011 July 27;8(1):54.
- Constipation
- Gastro-esophageal reflux (heartburn)
- Lethargy
Other short-term or reversible effects observed in clinical studies:
- Anemia
- Bad breath (halitosis)
- Decreased amino acid levels
- Flu-like symptoms or fatigue
- Itching (pruritus)
- Swelling of feet
A ketogenic diet alternating with fasting did not affect quality of life or cognition among people with malignant glioma in a small study.11Voss M, Wenger KJ et al. Short-term fasting in glioma patients: analysis of diet diaries and metabolic parameters of the ERGO2 trial. European Journal of Nutrition. 2022 Feb;61(1):477-487.
Potentially serious side effects
Some people eating a ketogenic diet have experienced the following potentially serious side effects, which may require medical attention:12Erickson N, Boscheri A, Linke B, Huebner J. Systematic review: isocaloric ketogenic dietary regimes for cancer patients. Medical Oncology. 2017 May;34(5):72.
- Functional changes in basal ganglia, granulocytes (neutrophils) and thrombocytes (platelets)
- High uric acid levels in blood (hyperuricemia)
- Inflammation of the pancreas (pancreatitis)
- Eye nerve damage (optic neuropathy)
- Carnitine deficiency, a metabolic state in which carnitine concentrations in plasma and tissues are less than the levels required for normal function
- Deficiencies of vitamins, minerals and enzymes
- Low blood calcium levels (hypocalcemia)
- Low blood magnesium levels (hypomagnesemia)
- Low or high blood potassium levels (hypo- or hyperkalemia)
- Low blood sugar (hypoglycemia)
- Dehydration
- Acidosis (a condition resulting from blood being too acidic, especially due to dehydration)
- Loss of appetite, especially among people with advanced cancer13Schmidt M, Pfetzer N, Schwab M, Strauss I, Kammerer U. Effects of a ketogenic diet on the quality of life in 16 patients with advanced cancer: a pilot trial. Nutrition & Metabolism. 2011 July 27;8(1):54.
- Weight loss: while several studies find that people who lose weight while eating a ketogenic diet lose more fat mass than lean muscle mass, people eating a ketogenic diet have also lost lean muscle mass in some studies. Both types of weight loss can be dangerous for people with cancer, especially advanced cancer.14Erickson N, Boscheri A, Linke B, Huebner J. Systematic review: isocaloric ketogenic dietary regimes for cancer patients. Medical Oncology. 2017 May;34(5):72.
Long-term side effects
Some people eating a ketogenic diet have also experienced these long-term side effects:15Branco AF, Ferreira A et al. Ketogenic diets: from cancer to mitochondrial diseases and beyond. European Journal of Clinical Investigation. 2016 Mar;46(3):285-98; Erickson N, Boscheri A, Linke B, Huebner J. Systematic review: isocaloric ketogenic dietary regimes for cancer patients. Medical Oncology. 2017 May;34(5):72.
- High blood lipids (hyperlipidemia): most common, although with conflicting reports of improvement in lipid profile16Sharman MJ, Kraemer WJ et al. A ketogenic diet favorably affects serum biomarkers for cardiovascular disease in normal-weight men. Journal of Nutrition. 2002 Jul;132(7):1879-85.
- High cholesterol (hypercholesterolemia), although with conflicting reports of improvement in cholesterol17Sharman MJ, Kraemer WJ et al. A ketogenic diet favorably affects serum biomarkers for cardiovascular disease in normal-weight men. Journal of Nutrition. 2002 Jul;132(7):1879-85.
- Heart muscle disease (cardiomyopathy)
- Kidney stones (nephrolithiasis)
- Thickening and hardening of the walls of the arteries (arteriosclerosis)
- Decreased growth in children and adolescents
- Loss of bone density (osteopenia or osteoporosis) or bone fractures
- Irregular menstrual periods
References