In my practice, discussions pertaining to nutritional advice and dietary support (aka what should I be eating?), are the most common conversations I have with patients. I often get asked about special ways of eating, also termed “fad diets”, which describes a prescribed way of eating with often various restrictions, with promises to combat and cure cancer. Fad diets include juicing, going vegan, fasting and the ketogenic diet. The ketogenic diet will be the focus of this article, and my goal is to explain how it works, how it may work therapeutically for those battling cancer, and times when the ketogenic diet may not be appropriate.
The ketogenic diet has a century-long history of clinical use, originally designed for severe epilepsy in children. It has become increasingly popular for other clinical intents, such as weight loss, diabetes, neurological conditions and cancer. Protocols and dietary composition can drastically vary, but what these protocols have in common is a low carbohydrate intake.
How Does the Ketogenic Diet (KD) Work?
The KD is generally a high-fat, very low carbohydrate diet, with protein being the macronutrient that can be the most flexible. The idea is that by restricting carbohydrate intake, the body adapts and a considerable shift in metabolism is induced, whereby the liver breaks down fats into ketone bodies to use as the body’s primary fuel, instead of sugars produced from carbohydrates. In the original, classic KD, it was thought that in order to achieve this, carbohydrate intake must be 10% of the total energy value of the diet. This ends up being a 4:1 ratio of fats to carbohydrates, and it was generally recommended to slowly increase this ratio from 1:1 to 2:1, 3:1 and finally to 4:1 to allow the individual to become accustomed to the increasing portion of fat in the diet. Another commonly employed method was to fast for 24 to 48 hours, and then start eating small meals with 90% fat. This dietary composition is very difficult to maintain, and would result in nutritional deficiencies.
Interest has grown about other ways to incorporate the ketogenic diet that is more palatable, healthy and sustainable. Medium chain triglycerides (MCT), obtained from MCT oil, allows faster absorption of fats into the diet and facilitates the production of ketone bodies, which allows more carbohydrates to be consumed, ideally in the form of fruits and vegetables. The modified mediterranean diet is another means to achieve high fat intake, primarily through healthy fats such as fish and olive oil, while still allowing high protein and moderate fruit and vegetable consumption.
Reducing carbohydrate intake while simultaneously increasing fat intake drastically decreases blood sugar, which in turn lowers insulin. This is one mechanism by which the ketogenic diet gained popularity among the cancer population, as cancer cells primarily utilize blood glucose as their energy supply. Further, it is well established that individuals with higher insulin levels have more aggressive tumours and higher relapse rates.
Other applications for the KD are type II diabetes and weight loss. Diabetes is characterized by poor glycemic control, and therefore a low carbohydrate diet is appropriately indicated. Diabetes is often associated with an overweight body type, and the KD is used as a popular dietary strategy for weight loss. The exact mechanisms as to why the KD diet achieves greater weight loss than other types of diets remains to be fully elucidated, but one hypothesis is that the KD diet influences appetite controlling hormones, leading to a decreased appetite. The presence of both diabetes and obesity confers poorer outcomes in those with, or with a history of, cancer, and therefore the KD could be a valuable tool to improve both of these conditions as well.
Ketogenic Diet and Cancer
A 2023 study of advanced cancer patients is the longest trial published to date that looked at the use of a ketogenic diet and overall survival. A total of 53 patents with stage IV disease (primarily non-small lung cancer, colorectal cancer and breast cancer) were instructed to follow a KD for either less than 12 months (average followed was 3 months) or more than 12 months (average followed was 37 months). There were 32 patients in the group that adhered to the diet for less than 12 months, and 21 patients that adhered to the diet for longer than 12 months. Follow up time ranged from 19 to 44 months, and at follow up, 31/32 patients had died in the short KD group, and 10/21 patients had died in the long KD group. These data suggest that a longer adherence to the KD diet in an advanced metastatic setting improves long term survival.(1)
A KD has also been shown to reduce tumour size. A study of 80 women with locally advanced breast cancer received chemotherapy plus a 12 week KD protocol, or chemotherapy alone. After the completion of treatment, surgery was performed. The women in the KD group had a greater reduction in tumour volume (27 versus 6 mm), as well as lower insulin levels and lower inflammatory markers. Therefore, a KD may assist with tumour size reduction in a neoadjuvant setting.(2)
Other studies have found that a KD may improve side effects. Patients with colorectal cancer undergoing radiotherapy were randomized into a KD group (n=18) or standard diet group (n=23). Patients in the KD group reported less pain and fatigue during treatment. Interestingly, body composition improved as well, resulting in less fat mass in the patients in the KD group.(3) Improved body composition has also been found in studies of head and neck cancer and pancreatic cancer, both cancers that often result in poor nutritional status.(4)(5)
Most studies studying the role of the KD in cancer treatment support that it is safe, and generally results in the lowering of insulin, blood sugar and body fat, which are all beneficial for those battling cancer. Less long term studies have been able to report effects on survival and tumour responses. A KD should be used on a case by case basis under the supervision of a qualified and experienced health care practitioner.
Risks of the Ketogenic Diet
I do not indiscriminately recommend the ketogenic diet for all of my patients. For those who attempt to adhere to the strict version encompassing 90% fat, extreme weight loss may occur, and while this may be beneficial for overweight individuals, weight loss can still be problematic and put someone at risk of cancer cachexia. Nutritional and electrolyte imbalances may occur, as well as halitosis and constipation. A low carbohydrate diet may result in hypoglycemia, and because a low carbohydrate diet often compromises fruits and vegetables, patients often consume less food with crucial antioxidants and fibre. While generally safe, do carefully consider whether a KD is right for you, and discuss the safe implementation of such a diet with an experienced integrative cancer specialist such as myself.
1 Egashira et al. Long term effects of a ketogenic diet for cancer. Nutrients, 2023;15(10):2334.
2 Khodabakhshi et al. Effects of Ketogenic metabolic therapy on patients with breast cancer: A randomized controlled clinical trial. Clin Nutr, 2021;40(3):751.
3 Klement et al. Eur J Nutr, 2022;61(1):69.
4 Klement at el. Strahlenther Onkol, 2022;198(11):981.
5 Ok et al. Anticancer Res, 2018;148(8):1253.
