Sugar and cancer – examining the science behind the claims

As you probably would guess, when I read articles in science, I tend to emphasize research on vaccines, cancer, and a few other related issues. There’s so much information out there, one has to focus or there will  not be enough time to watch college football games on Saturday. For years, one of the more popular questions I have seen is about sugar and cancer – does eating sugar cause or promote cancer?

A recent 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. To separate the science from the pseudoscience, we need to look at this more carefully. 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 avoid sugar. Sugar and cancer is much more complicated than that.

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 tumor 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, as in natural selection, because it provides some benefit to the cancer cell, such as causing blood vessels to supply the cells for nutrition and oxygen, or the ability to divide rapidly, whatever the feature is.

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 cell in your body can lead to cancer. Your blueberry kale shake 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 is a result of how cancers are grouped together (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.

Importantly, each of these cancers have 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 is based on preclinical research, that very rarely is brought into clinical trials or is successful in clinical trials. In fact, 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 the results of them. Simply, a lot of research that is publicly touted often ends up meaning nothing.

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.

Prior to 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. This hypothesis was eventually replaced by modern science – mutations in oncogenes and tumor suppressor genes (caused by viruses, environmental hazards, and random DNA errors) are responsible for malignant transformation. Warburg’s observations result from the mutations, and they are not the cause of cancer.

In his later years, Warburg doubled down on his “belief” that the driver of tumorigenesis is an 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.” In fact, 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, there are quacks and woomeisters who have grabbed onto Warburg’s hypothesis and 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 “cause” of all of these cancers.

Sugar and cancer – the new paper

A recent paper, published in Nature Communications by Peeters et al., 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.

Now 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 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.

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 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 to 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 have an effect on cancer development, at least with respect to sugar. There are reasons why a healthy adult should minimize 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 the cancer.

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 sun, HPV infections, obesity, and a handful of others. Sugar will not have a 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 needs to be fed with glucose in the blood.


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 some panacea for cancer.

What it does show us is a new strategy to attack cancer. If the Warburg hypothesis is shown to actually be a critical factor in cancer development, 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 cell (because it could have a bad effect on normal cells). This will take time (decades probably) before we can use this information to cure some types of cancer.

But for now, avoid sugar because of important health reasons that have nothing to do with cancer. However, just remember, the amount of sugar in your diet, unless you have uncontrolled blood sugar, will have little or no impact on cancer.


  • Peeters K, Van Leemputte F, Fischer B, Bonini BM, Quezada H, Tsytlonok M, Haesen D, Vanthienen W, Bernardes N, Gonzalez-Blas CB, Janssens V, Tompa P, Versées W, Thevelein JM. Fructose-1,6-bisphosphate couples glycolytic flux to activation of Ras.Nat Commun. 2017 Oct 13;8(1):922. doi: 10.1038/s41467-017-01019-z. PubMed PMID: 29030545; PubMed Central PMCID: PMC5640605.

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The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor
Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!