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The keto diet and cancer: Why some doctors believe ketosis ‘starves’ tumors

Can changing diet actually reverse the growth of cancer in the body?

Left: Flickr via NIH Image Gallery. Right: Flickr via Marco Verch.

Key Takeaways
  • The keto diet is known to be an effective tool for weight loss, but in recent years some–including some doctors–have claimed the diet has cancer-reversing qualities.
  • Although the theory might someday be proven correct, far more research is needed before scientists know whether the diet can be used as a safe and effective treatment for cancer.
  • A 2018 study did show one promising use for the keto diet in treating cancer, though it was purely used a supplemental tool in conjunction with a conventional approach.

Like any trendy diet worth its balanced portion of salt, the keto diet is said to hold transformative powers. Proponents say it can help people lose weight, improve mood and experience fewer epileptic seizures. For the most part, the science seems to back these claims up — though, to be sure, it’s not completely understood how exactly the keto diet affects mood (particularly depression), despite anecdotal evidence the diet might lead to clearer thinking and fewer symptoms of depression.

The boldest claim about the keto diet, however, is that entering a state of ketosis — which occurs when the body begins burning fat instead of glucose for fuel — can slow or even reverse cancer. It’s an idea that stems from a century-old theory about the primary cause of cancer.

​Cancer and metabolism

In the 1920s, a German biochemist named Otto Warburg observed that most cancers get their fuel differently than normal cells, a phenomenon dubbed the “Warburg effect”. The difference, in simple terms, is that cancer cells consume a lot more glucose than healthy cells. So, because cancer relies heavily on glucose, the idea is that putting your body in a state of ketosis — which lowers blood sugar levels — might effectively “starve” cancer cells because there’s less glucose to consume.

This ‘cancer thrives on sugar’ theory can be summed up like this, as outlined:

  1. Over half of the calories in standard diets come from carbohydrates.
  2. Carbohydrate digestion produces spikes in blood glucose which in turn causes a spike in insulin.
  3. Insulin’s job is to move glucose from the blood into cells.
  4. Cancer cells typically have many more insulin receptors than normal cells.
  5. Limiting carbs restricts the movement of glucose into cancer cells.
  6. When glucose is in short supply, the body will increase its use of fats as fuel.
  7. The liver converts some of this fat to energy molecules called ketones.
  8. Most normal cells (including brain tissue) readily adapt to using ketones.
  9. Tumor cells suffer because they are not as fuel flexible as normal cells.
​A ‘blueprint for the destruction of cancer’?

One of the most vocal proponents of the keto-diet-as-cancer-treatment theory has been Dr. Thomas Seyfried, a cancer researcher and professor at Boston College. Several years ago, Seyfried said that the keto diet actually beats chemotherapy for some types of cancer, a claim founded in his rather controversial belief that cancer is primarily a mitochondrial metabolic disease. In a recent paper, Seyfried outlined a cancer-treatment approach that he thinks could be the “blueprint for the destruction of cancer,” as he toldU.S. News & World Report:

“It’s called ketogenic metabolic therapy,” and he says in this context, “the ketogenic diet shouldn’t be considered a diet like green salads or other such stuff. It’s essentially medicine, and the process primarily tries to remove one of the driving fuels for the disease, which is glucose, and transition the whole body over to ketones, which the tumor cells can’t use as a fuel.”

“It’s a cocktail of drugs and procedures and foods and they all work synergistically to gradually eliminate the tumor while maintaining the health and vitality of our normal organs. The whole goal of this metabolic therapy, which involves the ketogenic diet, is to gradually degrade and eliminate tumor cells without toxicity so the patient emerges from the therapy healthier than when they started.”

Some have argued that Seyfried has “put the cart in front of the horse” in his past claims, and it should be noted that some prior studies which ostensibly show the keto diet’s cancer-reversing properties fail to demonstrate conclusively that it was ketosis, and not another factor, that helped beat cancer.

Ultimately, more research on the keto diet and cancer is required before doctors can responsibly recommend it as a standalone treatment.

“Most of the work in this field is still pre-clinical, meaning it’s been conducted in animal models,” Angela Poff, a research associate in the Department of Molecular Pharmacology and Physiology at the University of South Florida, told U.S. News & World Report. “It’s been done in various cancer types, but most of the work has been done in brain cancer specifically. But there’s very little clinical data all around. There’s some case reports and very small preliminary clinical studies in small groups of patients, usually very late-stage patients with various types of cancers. So in the clinical realm, which is the most important in telling us whether this is going to be useful, we have a long way to go.”

​Another use for the keto diet in cancer treatment

In July 2018, a study published in the journal Nature described how researchers used the keto diet to help a cancer-treating drug become more effective.

Recently, scientists have been experimenting with a new class of cancer drugs that target a cell signaling pathway called phosphatidylinositol-3 kinase. Studies have found mutations in this kinase as cancer develops, so the aim of the new drugs is to block the pathway with the hopes of stopping tumor growth.

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But researchers found that taking these drugs seems to cause spikes in blood sugar, which reactives the pathway and effectively kills the purpose of the drugs. In the 2018 study, researchers decided to use the keto diet as a way to control glucose levels in the body.

“The ketogenic diet turned out to be the perfect approach,” study author Benjamin D. Hopkins, a postdoctoral associate at Weill Cornell Medicine in New York City, NY, Hopkins, told Medical News Today. “It reduced glycogen stores, so the mice couldn’t release glucose in response to PI3K inhibition.”

“This suggests that if you can block spikes in glucose and the subsequent insulin feedback, you can make the drugs much more effective at controlling cancer growth.”

The study authors noted that the promising results don’t suggest that the keto diet on its own has any cancer-reversing effects. What’s more, they noted that a group of mice in the study that was placed on the keto diet but didn’t receive any cancer drugs actually developed cancer at faster rates than the other mice.


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