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Home » Does sugar cause cancer? Another dumb myth to be debunked

Does sugar cause cancer? Another dumb myth to be debunked

There is a lot of misinformation about sugar, but one is that it might be linked to cancer. Although there is some early research that may show a link between sugar and cancer, there is not robust clinical evidence supporting a link.

A 2017 paper in Nature Communications seemed to encourage the people who are pushing an association between sugar and cancer. Of course, our usual suspects of pseudoscience and false healthcare jumped on board with their clickbait headlines trying to scare everyone about sugar and cancer.

But what are the facts about sugar and cancer? Should you avoid eating a diet high in sugar and carbohydrates? Well, probably, but not because of cancer.

That’s why we are here. We need to look at this more carefully to separate science from pseudoscience. What we’re going to see is that you’re not going to get cancer from putting a couple of teaspoons of it in your coffee. And you’re not going to cure cancer by avoiding sugar. Sugar and cancer are much more complicated than that.

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The quick cancer primer

Cancer is a group of diseases characterized by abnormal cell growth which can invade or metastasize to other tissues and organs. Although people use tumors and cancer interchangeably, not all tumors are cancer. There are benign tumors that do not metastasize and are not cancers.

Cancer usually requires numerous, up to 10, independent genetic mutations in a population of cells before it can become a growing, metastatic cancer. Each mutation is selected for, like natural selection, because it provides some benefit to the cancer cell, such as causing blood vessels to supply the cells with nutrition and oxygen, or the ability to divide rapidly, and many more features that are necessary for a cancer cell to survive.

These mutations aren’t “naturally” a part of the cell’s physiology. Moreover, these mutations can have a lot of different causes – environmental (like smoking or UV radiation), viral (hepatitis B and human papillomavirus are the most famous), heredity, and maybe other things. These mutations are more or less random, and they can’t be prevented by anything special – if only it were that easy.

There are a few things you can do to prevent cancer, such as quitting smoking, staying out of the sun, getting your hepatitis B and HPV vaccinations, not drinking alcohol, keeping a low body weight, and eating a balanced diet. But even if you are a paragon of healthy living, a random mutation in some cells in your body can lead to cancer. Your blueberry kale smoothie is not going to do anything to prevent this. And it doesn’t sound very appetizing.

Moreover, despite the claims across the internet, cancer is not one disease.

The National Cancer Institute claims that there are over 100 types of cancer.  Cancer Research UK states that there are over 200 types of cancer.  The American Cancer Society lists over 70 types of cancer (although some are more classes of cancer rather than a single type).  Wikipedia lists over 180 different cancers. The variances in numbers are a result of how cancers are grouped (like liver cancer, which may be several different cancers) or how they are characterized. The consensus is that there are over 200 cancers, maybe a lot more since some cancers have subtypes.

Importantly, each of these cancers has different etiologies (causes), pathophysiologies (development), treatments, and prognoses. When someone is called a “cancer researcher,” they are rarely studying all cancers, but they’re studying one small part of the story of one of the 200 or so cancers.

One last thing. A lot of our ideas about what may or may not cure cancer are based on preclinical research — the vast majority of which never make it to human clinical trials. There seems to be a lot of evidence that it is difficult, if not impossible, to repeat the preclinical studies, so it makes it difficult, if not impossible, to accept their results. Simply, a lot of research that is publicly touted often ends up meaning nothing.

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Sugar and cancer – the Warburg effect

I’ve written about the Warburg effect before, but it bears repeating. Essentially, the effect describes how most cancer cells predominantly produce energy by a high rate of glucose metabolism as opposed to normal cells’ low use of glucose.

This whole area of cancer research can be laid at the feet of Nobel laureate Otto Warburg, a controversial Nazi sympathizer who discovered one of the critical cellular processes, respiration.

Not to be confused with respiration through the lungs, cellular respiration is the metabolic reactions and processes within cells that convert biochemical energy (like glucose) from nutrients into adenosine triphosphate (ATP, the basic energy source for the cell) and waste products. This fundamental understanding of the biochemistry of the cell is taught to biology students all over the world. His discovery of cellular respiration is certainly a critical one to our understanding of cellular physiology.

Before working for the Nazis, Warburg observed that most cancer cells produced energy by a high rate of glycolysis — glucose metabolism — in the absence of oxygen. Normal cells have a low rate of glycolysis while consuming oxygen. In general, rapidly growing tumor cells have glycolysis rates that are 200X higher than normal cells, even if oxygen is present, where the normal metabolic process, oxidative phosphorylation, could be supported.

In oncology, the “Warburg hypothesis” states that this change in metabolism is the fundamental cause of cancer. Modern science eventually replaced this hypothesis – mutations in oncogenes and tumor suppressor genes (caused by viruses, environmental hazards, and random DNA errors) are responsible for malignant transformation. Warburg’s observations of cancer did not result from sugar (or glucose) but from random mutations.

In his later years, Warburg doubled down on his “belief” that the driver of tumorigenesis is insufficient cellular respiration caused by damage to mitochondria. There is simply no evidence that ever supported his belief that this caused cancer.

As he grew ever more defensive about his hypothesis, he even invented a quote from Max Planck, a Nobel laureate in physics, that said “Science progresses not because scientists change their minds, but rather because scientists attached to erroneous views die, and are replaced.” Science progresses through evidence derived from the scientific method, not because someone whines that their unsupported ideas are not being accepted.

Despite my rather negative opinions of Warburg, his essential observations are the foundation of some areas of research in cancer treatment. No, the Warburg hypothesis has been roundly debunked, but only when looking at it as a “cause” of cancer. However, his data have been repeated many times, and there are bodies of research that use his fundamental research to develop drugs that can attack some cancer cells.

As the estimable Orac once wrote,

…it is now fairly clear that abnormalities in cancer cell metabolism are very important in driving cancer growth and could well represent targets for cancer therapy. AS a result of these new data, studying the metabolism of cancer cells has become a much hotter topic of research than it has been in the past. Everything old is new again, it seems. Why cancer cells might have an advantage due to the Warburg effect is a matter of debate, although, given how tumors frequently outgrow their blood supply, being able to maintain themselves in low oxygen situations would be advantageous.

Unfortunately, some quacks and woomeisters have grabbed onto Warburg’s hypothesis about cancer and sugar, then they have taken it in some illogical and pseudoscientific directions. The Warburg hypothesis may be an important direction for research into the treatment of some of the 200 different cancers – but it probably is not the underlying “cause” of all of these different cancers.

Sugar and cancer research

In a paper published on 13 October 2017 in Nature Communications, Johan M. Thevelein, Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU Leuven, Flanders, Belgium, and colleagues suggested that the Warburg effect creates a “vicious cycle” which stimulates oncogenic potency. In other words, glycolysis, by grabbing glucose from the bloodstream to fuel the cell without oxygen, may be an important factor in the growth of some cancer cells. According to the authors, this discovery might provide evidence for a positive correlation between sugar and cancer.

Before we all head into our kitchen and throw out everything that contains sugar, I need to mention a couple of points about the study.

First, this research was done on yeast cells that contain Ras proteins which arise from mutations in cells that lead to cancer. The researchers used yeast as a model organism to examine the connection between this protein’s activity and high sugar metabolism in yeast. So, yeast was used as a surrogate for cancer cells.

Yeast loves sugar. It turns it into alcohol, without oxygen – this is the basis of nearly all fermentation for spirits, beer, and wine.

Second, this result is way early in the research pathway to clinical utility. We would need to see if these results can be applied to cancer cells, and then to the development of drugs that stop glycolysis in cancer cells.

However, this study does raise some serious concerns about how sugar may stimulate cancer cells. Simply, some cancer cells may use excess sugar in the blood as a form of fuel to survive and grow.

But still, it’s not a reason to throw out all of the sugar in your pantry, avoid a chocolate chip cookie, or never touch ice cream. There are no claims here that sugar causes cancer. There may be other reasons to throw out the sugar, but not cancer.

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Sugar and cancer – what we can say

For most healthy adults, control of blood sugar is highly efficient, so sugar consumption is not going to have a material impact on cancer pathophysiology. A non-diabetic adult should have a fasting blood glucose level upon awakening which should be under 100 mg/dl. A couple of hours after a meal, the blood glucose should be less than 140 mg/dl.

This is a highly regulated system, where the body releases insulin after a meal causing glucose to be absorbed by various cells in the body. Another hormone, glucagon, is released by the body when the blood glucose gets low, causing more glucose to enter the blood. In normal adults, blood sugars are kept in a very narrow range by the feedback loops for insulin and glucagon.

So if you’re worried about sugar and cancer, and you have healthy blood glucose regulation, there isn’t much you can do to affect cancer development, at least for sugar. There are reasons why a healthy adult should minimize the consumption of sugars that contain glucose (like table sugar or sucrose). A diet high in sugar is a significant risk factor for developing type 2 diabetes, which has complications that could be subjectively worse than cancer.

It’s important to note that diet is just one factor in cancer. Many cancers do not exhibit the Warburg effect, and, thus, sugar has little or no effect on the growth and development of these cancer cells.

Smoking cigarettes is still the number one cause of cancer. If you continue to smoke, but reduce your sugar consumption, I doubt that you’re going to have a significant effect in reducing your risk of cancer. The same with other causal factors for cancer – exposure to the sun, HPV infections, obesity, and a handful of others. Sugar will not have an effect in changing your risk of cancer under those conditions.

Reducing sugar will also not cure any cancer – remember, there is no way to remove glucose from your blood. Well, I guess if there were a way, you’d die. Your brain, heart, and nearly every single cell in your body need to be fed with glucose from the blood. If you were able to eliminate every µg of glucose from your diet, your body still can produce glucose in an attempt to keep blood levels of sugar high enough to survive.

All that being said, there are proposals for clinical trials that compare the standard of care treatment of cancer with a group that receives the same care but a diet to reduce sugar consumption. They are not proposing that reducing or eliminating sugar will “cure” cancer, but they hypothesize that it might improve outcomes.

There are thousands of articles published on glycolysis and cancer, so it is a field of study where a drug may be discovered that could inhibit glycolysis in the cancer cell, thereby killing it. There are dozens of areas of research, from kidney cancer to prostate cancer to many others where the metabolism of sugar is a critical research strategy.


The important take-home point, at least from my analysis, is that avoiding sugar has more important health benefits, like avoiding type 2 diabetes. But avoiding sugar as a strategy to prevent, treat, or cure cancer? I don’t think this research has shown us that sugar avoidance is a panacea for cancer treatment or prevention.

What it does show us is a new strategy to attack cancer. Suppose the Warburg hypothesis is shown to be a critical factor in the pathophysiology of some of the 200 or so cancers. In that case, we can tailor-make medications that could block glycolysis in cancer cells. Of course, we also need to target these new drugs to the cancer cells (because it could have a deleterious effect on normal cells). This will take time (decades probably) before we can use this information to cure some types of cancer.

You are not going to prevent or cure cancer by going on a carbohydrate-free diet today. You simply cannot remove all of the glucose from your blood, or you will die. However, I think that sugar and cancer are interesting areas of research that may lead to effective treatments, but only at the biochemical level of cancer cells, not by changing your diet.

Importantly, I could find no research that followed up on the findings of the research I mentioned above. A recent review of the research on sugar and cancer stated that “current evidence for cancer incidence and mortality is not conclusive.”

Sugar does not cause cancer, although obesity is linked to a higher risk of cancer, so consuming too much sugar could indirectly cause cancer. But obesity is caused by much more than sugar.


Michael Simpson

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