Ketogenic Diet and Cancer

The ketogenic diet, often just called "keto," is now under study for its potential role in both cancer prevention and treatment. Whether or not it offers real benefits, however, is a complicated question.

First, cancer is not a single disease. It is a broad collection of diseases. It's possible that a keto diet may be helpful for one type of cancer but harmful for another. It's also important to consider how a keto diet would work alongside other treatments, like chemotherapy and radiation. That's an essential conversion to have with your doctor if you have cancer and are looking at diet changes.

This article looks at what the keto diet is, and how it might work to prevent or help fight cancer. It also gives a brief summary of what the relatively new research says about the possible benefits of keto, as well as side effects and risks.

Defining the Ketogenic Diet

The keto diet is high in fat (55% to 60%), low in carbohydrates (5% to 10%), and is protein "neutral." At 30% to 35% of all calories, it does often have a slightly higher amount of protein than the typical Western diet.

It is important to note that these nutritional ratios are not aligned with the 2020-2025 Dietary Guidelines for Americans. These guidelines are jointly published by the U.S. Department of Agriculture and the U.S. Department of Health and Human Services.

The general U.S. guidelines call for more carbs and far less fats and proteins. Even though keto restricts carbs, it differs from many low-carbohydrate diets that are made up of 20% to 30% carbs.

Keto-Adaptation

The goal of the keto diet is to burn fat instead of sugar as the body's energy source. When carb intake is significantly reduced, the body switches to burning fat, a process that produces ketone bodies. This is called keto-adaptation.

This diet-based ketosis differs from the diabetic ketoacidosis, a dangerous condition.

The Keto Diet and Disease

Keto has been found to lead to weight loss, at least over the short term. It also has proven helpful in limiting seizures in people with medication-resistant epilepsy, and is under study for a possible role in conditions that range from Parkinson's disease to autism.

Possible Mechanisms in Cancer

The research on using the keto diet in cancer is new, and findings are not well established. So it's helpful to look at how the diet may affect cancer cells and normal cells in the body.

Keto may have benefits, for at least some cancers, in a few different ways. Some have to do with how keto might help suppress growth in cancer cells. Others are focused on cancer prevention.

Effects on Cancer Cells

One possibility for how keto might work is based on what feeds cancer cells, and how keto might slow their growth by essentially "starving" them. This part of the science isn't new at all: Scientist Otto Warburg first described the Warburg effect, which led to his 1931 Nobel Prize in Physiology and Medicine. Basically, his theory was that glucose (sugar) feeds cancer cells.

As a result, sugar often has been blamed as the cause of cancer growth. With keto, though, the diet actually exploits the cancer's dependence on glucose. From lab studies, it appears that at least some cancer cells have difficulty using ketones as a source of energy. These cancer cells are less likely to go through keto-adaptation because of biochemical changes linked with their ability to use ketones.

The theory is that by causing ketosis, on purpose, the keto diet gives healthy cells an advantage over cancer cells. That's because cancer cells may not adapt as well to using ketones for growth.

It's possible that keto, in theory, might play a role in cancer because it leads to lower insulin levels in the body. It's known from research that both insulin and insulin-like growth factors can stimulate the growth of cancers.

In order for cancers to grow, they also need to develop new blood vessels to support the tumor. This process is called angiogenesis. In a mouse model of the brain cancer glioma, keto was found to reduce angiogenesis.

Finally, it's thought that ketone bodies might actually have a direct toxic effect on cancers themselves. One study looked at the effect of added ketone on cancer cells grown in the lab, and on mice with metastatic cancer. In the lab, ketone supplements limited both the health and growth of the cancer cells. In the mice with cancer, additional ketone was linked to longer survival: 50% to 68% longer, depending on the specific ketone body used.

Possible Mechanisms in Prevention

In theory, the keto diet also may work in ways that could reduce the risk of at least some cancers.

Cancer begins when a series of mutations occur in a normal cell. There may be inherited genes at work, but most mutations are acquired over time via oxidative stress. This refers to an imbalance of free radicals and antioxidants, such that free radicals outnumber the antioxidants.

Free radicals are unstable molecules that can be produced by cancer-causing agents or by normal processes in the body. The theory behind eating a diet rich in antioxidant foods is that they work chemically to "neutralize" free radicals. They help to keep them in check and restore the balance. In one study, the ketone body B-hyroxybutyrate has been shown to suppress oxidative stress.

Ketone bodies offer two potentially positive actions here. First, they reduce the production of free radicals. At the same time, they boost antioxidant capacity in the body. This may be important for people who are living with cancer, because cancer cells develop new mutations. These changes can make the chemotherapy and targeted drugs that were working become ineffective.

That said, and as will be discussed below, there are still questions about whether such benefits might be lost because a keto diet limits fruits and vegetables that also may have positive effects.

Potential Benefits in Cancer Prevention or Treatment

The research into how a keto diet may work in both cancer prevention and treatment is in its infancy. There are relatively few human studies to date, but animal and lab studies exist looking at how ketosis may play a role in cancer.

Preclinical Studies (Lab and Animal)

Animal studies, along with human cancer cells grown in the lab, don't directly show what will happen in humans but they do shed light on a potential role for keto in cancer.

Overall, animal studies suggest that keto may have anticancer effects with most cancers. A 2017 review of existing studies found that 72% of them showed a keto diet had an anti-tumor effect on cancer in animals. In this review, a pro-cancer effect (worsening of a tumor because of a keto diet) was not seen.

Other pre-clinical studies have found that different types of cancer, or their subtypes, may respond differently to keto. For example, the diet had an anticancer effect on some cancer cells but seemed to have a pro-cancer effect in kidney cancer and BRAF-positive melanoma.

The fact that BRAF V600E-positive melanoma in a mouse study showed significant growth on the keto diet. This raises concern that keto may have different effects not only on various cancer types, but the specific molecular changes present that drive tumor growth.

Overall, for good or bad, keto appears to have an effect on the metabolism of cancer cells. In a 2019 study, the keto diet was found to suppress cells in ways that may go beyond its action on the energy supply of the cells. What mechanism may be at work, though, is unknown.

Human Studies

Most of the keto diet studies in people with cancer have been small, and many have focused primarily on safety at this time.

The strongest evidence has been seen in glioblastoma, the most common and aggressive type of brain cancer. There is also good evidence for a potential keto benefit in other cancers, including lung cancer, prostate cancer, colon cancer, and pancreatic cancer.

While animal studies are helpful, the situation in humans may be different. One study discussed earlier showed significant growth of BRAF-positive melanoma in mice on a keto diet. Yet in a small trial with only a few humans who had BRAF-positive melanomas, one appeared to benefit from the keto diet.

A 2018 study of keto's effects on women with ovarian or uterine cancer primarily looked at safety, but it was encouraging in other ways. The diet did not negatively impact quality of life for the women, and may improve physical function, reduce fatigue, and decrease food cravings.

Side Effects, Risks, and Contraindications

With any approach to cancer, the potential benefits must be weighed against risks. The same is true when thinking about adopting a keto diet. Here are some of the more common problems that arise.

Side Effects

When people begin the keto diet, it's common to have symptoms that have been called the "keto flu." This can include fatigue, nausea, vomiting, a lower exercise tolerance, constipation, and other digestive system side effects.

Risks

These side effects as well as the metabolic effects of the keto diet can pose some risks, including:

• Dehydration
• Kidney stones
• Gout
• Hypoglycemia

People should also be aware that keto can cause a false positive alcohol breath test.

Long term side effects may include low protein levels in the blood (hypoproteinemia), fatty liver disease, and low levels of key vitamins and minerals. Since the diet is hard to maintain, and research is relatively new, all of the potential longterm effects are unknown.

Potential Risks Related to Cancer

While few studies have been done, the keto diet presents some possible risks for people with cancer. Here are a few to know, and discuss with a doctor, before making any diet changes.

Dietary Needs and Possible Deficiencies

The keto diet is strict, and it could be hard to get all of the important nutrients needed in a healthy diet. The increase in fat intake could be a problem too. For example, a low-fat diet has been linked to a lower risk of recurrence with some types of breast cancer. On the other hand, keto may help some people lose weight; obesity is linked with a higher risk of breast cancer recurrence.

When you are coping with cancer, or if you have a hereditary disorder of fat metabolism, your body may not function the same way it does in people who are cancer-free. Just as cancer cells may be unable to process the proteins and fats, it's possible that healthy cells may have problems as well.

A significant concern is that of restricting foods such as fruits. There are many studies that have found a lower risk of cancer in people who eat a greater number of fruits and vegetables.

Since dairy products are restricted on some keto diets, a lack of vitamin D also may be a concern. That said, due to the association of low vitamin D levels with poorer outcomes in some cancers, everyone with cancer should have a blood test to determine their vitamin D level, and talk to their oncologist if the level is low (or within the low end of the normal range)

Fiber

Since the ketogenic diet restricts fruits and legumes, it may also reduce fiber intake. Fiber can be thought of as a "prebiotic" or a food that feeds your gut bacteria.

For people with cancer treated with immunotherapy, a diverse gut microbiome is associated with greater effectiveness. Though probiotics did not appear to help, a high fiber diet did. Fiber also helps maintain bowel function. Current USDA guidelines recommend an intake of 23 to 33 grams of fiber daily.

Fatigue

Keto could make fatigue associated with cancer (cancer fatigue) worse at the start, and many people considered this fatigue to be one of the more annoying side effects of cancer treatment.

Cancer Cachexia

While praised as a method to lose weight, weight loss may be detrimental to someone living with cancer. Cancer cachexia, a syndrome of unintentional weight loss and muscle wasting, is thought to be the direct cause of 20% of cancer deaths.

Contraindications

The keto diet should be avoided by women who are pregnant, wish to become pregnant, or are breastfeeding. It should also be used with caution in people with diabetes, and only under the careful guidance of a doctor. There are several medical conditions for which keto should absolutely not be used. These conditions include:

• Liver failure
• Pancreatitis
• Certain hereditary syndromes, such as pyruvate kinase deficiency, and other disorders of fat metabolism.

Diet and Cancer

We know that what we eat is important. Just as higher octane gasoline may lead to better function in cars, our bodies function most efficiently when we give them the right fuel. When it comes down to diet and cancer, however, the research is in its infancy.

A diet high in fruits and vegetables and low in processed meats is linked to a lower risk of many cancers. Less is known about how specific foods and diets affect a cancer already present. Fortunately, there are currently many clinical trials in place designed to answer these questions.

Summary

The keto diet is designed to increase the body's production of ketones, and force the body to burn fat for energy instead of sugar. Because they are familiar with the chemical action of ketones, scientists are asking if the power of these "mechanisms" could be used to prevent cancer. They also are researching how a keto diet might be used in cancer care to deliver better outcomes.

A Word From Verywell

There are ways the keto diet may play a role in cancer prevention or treatment, but how those theories play out in people living with the disease is uncertain. If you are asking about the role of keto in cancer care, you are in a good place. It's a sign that you are being an advocate in your own health care. Talk to your doctor about whether a keto diet may be a good choice.