In the news: Can a keto diet prevent and treat cancer?

Last Updated : 31 May 2022

Recent news stories reported that a ketogenic diet – a dietary pattern high in fat and protein while low in carbohydrates – can prevent and treat cancer. While the study behind these news stories adds important insights to the wider scientific effort to cancer prevention and treatment, there are a few things to keep in mind when reading the headlines.

The study behind the headlines

The study behind the news was carried out by researchers from the University of Pennsylvania in the United States with the aim to investigate whether different dietary patterns could help to prevent the development or growth of bowel cancer, also known as colorectal cancer.¹ Colorectal cancer is one of the most common types of cancer in the Western world and has one of the highest mortality rates of all cancers. At the same time, many cases could potentially be prevented by adopting a healthier dietary pattern and lifestyle.

The study involved six groups of mice in a laboratory who were given a treatment to initiate the development of bowel cancer. The mice were then fed on diets containing the same amounts of protein but different fat-to-carbohydrate ratios. Two of the diets were described as ketogenic, containing 90% fat and zero carbohydrates. The researchers observed that increasing fat intake was associated with a smaller number and size of bowel cancers, and longer survival duration. The cancer-suppressive effect of the ketogenic diet appeared the same regardless of whether the diet was started before or after the researchers gave the mice the cancer-causing treatment. This suggests that the ketogenic diet might be effective for both the prevention and treatment of bowel cancer.

The explanation for this appeared to be so-called ketones, which are produced by the liver as an alternative energy source when the body is low on glucose, as may be seen during starvation or when following a low carbohydrate diet. Specifically, a ketone called β-Hydroxybutyrate (BHB) was found to decrease cell turnover (i.e., the replacement of old cells with newly generated ones) in the bowel, and so also decreased the growth of cancer cells.

The researchers explored this further using human bowel cells donated from people with and without colorectal cancer. When the cells were grown with BHB, the ketone likewise suppressed the growth of both healthy and cancerous human cells. The researchers, therefore, suggest that a ketogenic, but high fibre, diet might provide the best protection against the development of bowel cancer.

What to keep in mind when reading the study’s conclusions?

• This is early-stage laboratory research.

Overall, only a very small fraction of laboratory studies eventually become recommended treatments by themselves. In this case, the research was performed in animals and in vitro human cells and current results can’t be directly applicable to humans. Further research may be needed to validate the effects on cancer development and the underlying biological mechanism. If confirmed, there is still a substantial process ahead before findings can become a recommended treatment as they need to be proven effective, feasible, safe and ethical when used in people.

• A ketogenic diet could have harmful effects.

When the body is breaking down fat to generate ketones, this is in effect an emergency reserve state because the body is short on its normal fuel supply of glucose, and not the ideal condition to be maintained in the long term. This study has demonstrated that a high level of the ketone BHB suppressed the growth not only of cancer cells but also of the normal healthy cells that line the bowel. The extent of this effect – for example, if it would also affect the turnover of healthy cells in other parts of the body - is an important point to consider, though it has not been addressed in this study. Ultimately, it’s important to note that following a restrictive high-fat, low-carbohydrate diet can have harmful effects if it deprives people from important food groups like fruit, vegetables and whole grains that provide a wide range of nutrients essential to keep good health. A ketogenic diet can also be high in saturated fats and red and processed meats (which have been linked to bowel cancer) which are recommended to be limited in the diet. This altogether may counter any potential protective benefit from increased BHB.

• Cancer patients should not change their diet without medical supervision.

If considering a ketogenic diet, alongside the above potential effects, people with existing bowel cancer may already have lost weight, be receiving intensive or debilitating treatment, or have increased psychological vulnerability among other effects of their illness. Undergoing dietary restrictions and inducing low glucose may be further detrimental to their health and wellbeing. Alternatively, if a treatment based on BHB were to be developed and trialled, its role alongside established cancer treatments would need to be carefully considered.

• The overall combination of modifiable risk factors may have a greater influence on the risk of bowel cancer development and progression.

Hereditary, biological, lifestyle and environmental factors usually have a combined influence on a person’s overall cancer risk. While some risk factors such as age and genetics cannot be changed, following a healthy diet and lifestyle, in general, could have a greater effect on reducing bowel cancer risk than a single dietary strategy. For example, maintaining a healthy weight, avoiding smoking, limiting alcohol, exercising in line with recommendations, and eating a diet high in fibre, fruit, and vegetables and low in salt, sugar and saturated fats, including limiting red and processed meats.

What do authorities say on this topic?

• The World Health Organization advises that a healthy diet protects against malnutrition and many chronic diseases including cancer. This includes eating at least five portions of fruit and vegetables daily, whole grains, nuts, and legumes. WHO advise reduced-fat dairy foods and lean meats, with less than 30% of daily energy coming from fats, less than 10% from saturated fat, and trans fats eliminated where possible.²
• The World Cancer Research Fund (WCRF) advises limiting red meat intake to about three portions a week, equivalent to about 350-500 g cooked weight (525-750 g raw weight) a week, and eating very little or, ideally, no processed meat. Both have been linked to a higher risk of bowel cancer, with the evidence being particularly strong for processed meats.³
• WCRF also advises that obesity and a poor overall diet can have a strong influence on your risk of developing cancer, while diets high in fibre from vegetables, fruit, whole grains, and legumes, can protect against bowel cancer.⁴
• The European Commission presents the position of different European and international organisations on the modifiable risk factors for bowel cancer. The specific statements differ, but overall the organisations support the likely reduction in risk from increased intake of fibre, whole grains, fruit, vegetables and milk/dairy, that red meat probably causes bowel cancer and that processed meat is a definite cause.⁵

Sources

1. Dmitrieva-Posocco, O., Wong, A. C., Lundgren, P., Golos, A. M., Descamps, H. C., Dohnalová, L., ... & Levy, M. (2022). β-Hydroxybutyrate suppresses colorectal cancer. Nature, 1-6.
2. World Health Organization. (2020). Healthy diet. Retrieved from https://www.who.int/news-room/fact-sheets/detail/healthy-diet
3. World Cancer Research Fund. (n.d.). Red and processed meat and cancer risk. Retrieved from https://www.wcrf-uk.org/preventing-cancer/what-can-increase-your-risk-of-cancer/red-and-processed-meat-and-cancer-risk/
4. World Cancer Research Fund. (n.d.). Poor diet and cancer risk. Retrieved from https://www.wcrf-uk.org/preventing-cancer/what-can-increase-your-risk-of-cancer/poor-diet-and-cancer-risk/
5. European Commissions. (n.d.). Knowledge for policy: Health Promotion and Disease Prevention Knowledge Gateway. Retrieved from https://knowledge4policy.ec.europa.eu/health-promotion-knowledge-gateway/colorectal-cancer-table-2_en