No Sugar, No Cancer? A Look at the Evidence

photo of sugary foods like candy, donuts, and cupcakes

Sugary foods are plentiful in the modern Western diet. Do they increase one's cancer risk?


Memorial Sloan Kettering President and CEO Craig Thompson is an expert on cancer metabolism. We spoke to him about common misconceptions regarding sugar and cancer.

  • Obesity — having too much body fat — is a clear risk factor for cancer.
  • Obesity is caused by consuming more calories than are expended over time.
  • Eating lots of refined carbohydrates, including foods with added sugar, can lead to obesity.
  • Body fat promotes inflammation, which can damage DNA and lead to cancer.

There’s a lot of confusing and misleading information on the Internet about the relationship between sugar and cancer. The notion that refined sugar causes cancer or that cutting sugar from the diet is a good way to treat cancer are two common — and incorrect — claims that turn up in a Google search.

That’s unfortunate, because there is important, real science to understand about diet and cancer. To help sort out fact from fiction, we spoke with MSK President and CEO Craig Thompson, who studies the relationship between metabolism and cancer.

There is no question that obesity is associated with an increased risk of cancer, and that the abundance of carbohydrates in our diet is one of the major foundations on which the worldwide epidemic of obesity is built.

The fundamental basis of obesity is eating more calories than you can burn over a period of time. Many people assume that if a person has a lot of body fat, it’s because they ate too much fat. That makes intuitive sense, but it isn’t the truth. Pretty much all you do with fats that you eat is burn them for energy.

The fats you put into your fat cells are by and large made from carbohydrates. But it took us 25 years to figure that out. And as we learned recently, some groups tried to discourage or prevent that research.

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How did we get into this obesity trouble?

As we emerged as a major agricultural nation after World War II, the United States was able to produce a tremendous amount of grains. And the caloric value of grains is not in their protein or in their fats primarily, but in their carbohydrates.

We also learned that we could refine those carbohydrates into things that were pleasurable to eat — sugar. So that was exploited, for good and for bad, to give us the soft drinks that we have today, to give us the kinds of high-caloric meals that allow people not to be malnourished. Because the first necessity in nutrition is not to have a balanced diet, but just to get enough calories to support us with the energy to live. Carbohydrates are the most immediate source of our ability to produce the energy needed to maintain our bodies.

But then the USDA developed the nutritional food pyramid and put carbohydrates at the base of it. The food pyramid wasn’t based on science. It was just what we could produce as a nation. That’s gotten us into trouble.

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Why is having too much stored-away fat dangerous?

We’ve learned that fat cells themselves are signaling cells. We used to think they were just storage depots, like the garage where you put your car, but we now know that’s not true. Fat cells, through the hormones they produce, are a major regulator of inflammation in the body.

Inflammation is a natural response to infection or injury. But inflammation also makes it more likely that you’ll damage the DNA of cells that survive, and this increases the chances that a cell might turn cancerous. More and more we’ve come to understand that cancer grows out of areas of regeneration and repair, places where there’s likely to be inflammation.

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Carbohydrates raise insulin levels. Could abnormal levels of insulin lead to cancer?

Insulin’s job is to tell the cells in our body, “Hey! There’s a lot of glucose. We should use it.” Therefore, if we could get people to produce less insulin, they might do better. But the real root problem of the worldwide obesity epidemic — and cancer as a result of obesity — has to do with too much caloric intake. It has little to do with abnormal insulin signaling.

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Where does the idea that cancer is “addicted” to sugar come from?

About 90 years ago, a German scientist named Otto Warburg noticed that tumor cells in a dish tended to consume more glucose than non-dividing normal tissues. He also noticed that although the cancer cells were consuming massive amounts of glucose, they weren’t taking advantage of the most efficient method of harvesting energy from that glucose, which is to essentially burn it using oxygen in the mitochondria. Instead, they converted the glucose to lactate, leaving much of the energy untapped. This has come to be known as the Warburg effect or Warburg metabolism.    

Pictured: A cell structure called mitochondrion imaged by transmission electron microscopy. Within mitochondria, sugars and fats are oxidized to produce energy needed for diverse cell functions.
Cancer Metabolism
Learn about the work Memorial Sloan Kettering scientists are doing in the area of cancer metabolism.
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Warburg assumed that cancer cells must have a defect in their mitochondria, because why else would they resort to this inefficient method of obtaining energy? But we now know that Warburg was wrong. Tumor cells possess functional mitochondria and rely on them for energy in some situations.

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Explain why it’s hard to “starve” cancer of sugar just by changing your diet.

Because your body has this interesting fail-safe system that never lets your blood glucose level drift below a certain number. So eating less sugar will just make the body use its remaining resources to produce the glucose on its own.

Everything about your biology has been naturally selected for at least 600 million years to make sure that no matter what you eat, you keep enough glucose in your system and don’t become deficient. So it’s very hard to affect the system by changing your diet.

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What about ketogenic diets? Can they lower your risk of developing cancer?

A ketogenic diet is when you restrict carbohydrates and eat more fat. On a ketogenic diet, you’re burning fats and your metabolic rate goes up just a little bit. It makes you use more calories from what you eat in just maintaining yourself every day. And you have very little ability to store the extra fats that you eat, so you pee them out as ketones. That’s why it’s called ketogenic. And it’s why people lose weight on a ketogenic diet — they’re getting rid of more of the calories that they consume.

So does a ketogenic diet help you decrease your chances of getting cancer? If you are overweight and it helps you lose weight, then yes, it does. If you can tolerate it, it’s perfectly fine. I was on a ketogenic diet for two and a half to three years back in 2004, 2005. I lost 40 pounds. But I eventually gave it up and I’ve since gained back most of the weight. It’s almost impossible to stay on a ketogenic diet for any significant length of time. Food just doesn’t taste the same. But I still don’t eat a lot of refined sugar in any way, form, or shape.

Now does a ketogenic diet matter once you have cancer? Does it help improve your cancer care? We have no evidence that that’s true, or that you should use a ketogenic diet while you’re receiving cancer treatment. In fact, a person going through cancer treatment might benefit from additional calories and nutritional support to help his or her body recover.

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What’s the bottom line for the average person?

Eat a balanced diet that avoids too many carbohydrates — especially refined carbohydrates that lack fiber and other foods with added sugars — and do your best to keep your weight down. That’s my best advice. 

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Very interesting!

It has been widely shown that sugar can be significantly reduced and maintained at a lower level via calorically restricted diets and therefore, have a therapeutic effect on cancer growth. In addition, there is also a large body of research illustrating the therapeutic effect of calorically restricted ketogenic diets for not only the treatment of cancer, but neurological disorders such as epilepsy. Please check out this recently published "Ketogenic Diet and Metabolic Therapies" edited by Susan A. Masino for a comprehensive summary of the utility of such diets.…;

If sugar doesn't effect cancer the way many new researchers suggest,,,,then why are you suggesting it is not the sugar per say but calories? I find the proof in that you use a radioactive sugar as a means to find cancer on a Pet Scan? I know it is horrible to have cancer (which I do) and feel you can't have that piece of cherry crumb pie yummy,,,because it's going to find and feed you're cancer,,,but after reading Cancer the Metabolic Disease I am convinced it does feed cancer. I wish There was scientific evidence to prove otherwise? If there is please leave a link,,,I wish I could debrief my Brian from believing sugar goes right to the cancer cells? I have even noticed a sensation in my tumor after eating that piece of pie,,,burning tingling?

Dear Patricia,

While it is true that some cancers avidly take up glucose (and thus can be visualized with a PET scan using radioactive glucose), it is not true that changing one’s diet by cutting out sugar will prevent cancer cells from obtaining glucose — for the reasons mentioned in the blog: Our bodies vigilantly monitor and correct the levels of glucose in the blood, maintaining them within a very narrow range, more or less regardless of diet. (The exception is people with diabetes, who have a problem regulating blood sugar.) Cancer cells have mutations that allow them to take up excess nutrients, including glucose, to fuel their growth. They will be able to obtain these nutrients regardless of a person’s diet. For more information on nutrition guidelines for cancer patients, see the following:…
For more information on the link between obesity and cancer risk, see:…

Thank you for your comment.


I had cancer. During my chemo, I could only tolerate vanilla ice cream milk shakes; nothing else. I have been cancer free now for 7 years!

I cut back on sugar when I was diagnosed with CLL. Important to note that I occasionally binged on sugar. I also have Ulcerative Colitis and cutting back on sugar really helped my reactive gut; I sleep better and feel better. It is possible then, that good sleep because of better diet; in my case less sugar, can decrease the progression of cancer, given the effect on sleep patterns.

Cancer treatment can severely impact the digestive system. I hear occasionally of people with cancer who try so hard to eat "perfect" diets while going through treatment, and end up not getting the nutrients they need, and/or really messing up their digestion. My advice is that eating something is better than eating nothing. Eat as healthily as you can during treatment, but don't beat yourself up if the only thing you can stomach is an Ensure shake or bland, white food. Just eat it!

I’ve had Non Hodgkins large B cell Lymphoma and Hodgkins Lymphoma I’ve done tons of chemo and radiation including experimental chemo along with surgery and two stem cell transplants and as of right now I’m good thanks to Sloan Kettering. I do have a question how do you feel about intermittent fasting?

Dear Joey, we’re glad to hear you’re doing well. We recommend that you discuss any diets you are considering with someone who is familiar with your medical history and is also knowledgeable about nutrition in cancer survivors.

You can go to… to learn about Nutrition Services at MSK, including how to make an appointment. Thank you for your comment and best wishes to you.

I am currently being treated for lung cancer. I need guidance on diet especially the relationship between sugar/carbs on cancer/cancer cells. There is so much confusing and at times contradictory reports about sugar and it's effect on cancer cells from self-proclaimed "experts". I value your research and your reports. Please give me guidance. Thank you.

Dear Jim, we’re sorry to hear about your diagnosis. We recommend that you ask your doctor or nurse for a referral to a nutritionist who specializes in working with people who have cancer. Thank you for your comment, and best wishes to you.

As a Stage IV prostate cancer survivor/ warrior I think we all have to be careful regarding internet claims of dietary claims of cancer cures related to any eating regime until research tells us otherwise . The subject is far more complicated than we can imagine where ALL interventions and outcomes vary as to type of cancer and stage , For example prostate cancer utilizes fatty acids versus glucose resulting in the inability of glucose tracer PET scans to detect cancer cells or the status of metastatic disease . As stated earlier the body has mechanisms to maintain a balance or homeostasis where for example the liver can create glucose through the process of gluconeogenesis from excessive dietary protein . I would only recommend to maintain a normal weight , avoid processed food , get regular exercise , and consult your medical oncologist regarding dietary needs during any treatment including radiation , chemotherapy , or any oral medications prescribed .

I currently have been battling stage 3c lobular and 2b ductal breast cancer. I've had 5 months of ACT, a double mastectomy with 19 positive nodes, and 38 days of radiation. My last two petscans were clear and I had been on Letrozole which packed on the weight, caused two fractured ribs and depression. Question one is who fo I lose weight on estrogen blockers and question two is all estrogen blockers give me depression and make me feel like I'm 100 with no quality of life. Does Sloan have any other therapies for my condition other than blockers...kind of desperate.

Dear Judy, we’re sorry to hear you’ve been through all this. If you are interested in consulting with an expert at MSK about what your options may be, including possible alternatives to estrogen blockers, you can call 800-525-2225 or go to for more information on scheduling an appointment. Thank you for your comment, and best wishes to you.

Thank you for this article. I work as a Clinical Registered Dietitian at a small hospital and cancer outpatient clinic. Encouraging patients to eat healthy and avoiding fad diets is always a challenge. I find the biggest challenge is for patients who are losing weight during treatment that are afraid to drink oral nutrition supplements because they have sugar in them. During cancer treatment my goal is to prevent weight loss in my patients so they can be as successful as possible during chemo and radiation. Again, thank you for this wonderful article.

I am looking for resources for cancer prevention via diet and lifestyle

We recommend that you contact the National Cancer Institute’s Cancer Information Service. They can be reached at 800-4CANCER. Thank you for your comment.

Recent research out of Belgium found that sugar "awakens" cancer cells. "The Warburg effect creates a vicious cycle through Fru1,6bisP activation of Ras, by which enhanced fermentation stimulates oncogenic potency," they write.

I have prostate cancer. I have been following it with psa's and BX for 5 years. My most recent BX showed gleason 3+4 rather than 3+3. right side only. Does this mean the tumor morphed from six to 7 or is there possibly a new tumor, or is it possible the 1st 2 BX were misread as 6 and not 7. My question truly is: does having a gleason 7 now change my game plan and what are my options for treatment, I am 62 years old and otherwise in excellent health. Thanks...Dave

ps I do see a urologic oncologist was just wondering your thoughts

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