Sugar doesn't cause - or feed - cancer.
This pervasive myth is propagated by wellness influencers who don't understand cancer biology to exploit health anxiety and sell pseudoscience.
If you’re sensing a theme, you’re not wrong! Health misinformation frequently gains legs because someone misrepresents basic science principles, scientific data, or wildly extrapolates a phenomenon that exists, but not in the context it is misapplied.
Cancer misinformation always sits in that space. I’m excited to start to dig into more cancer myths, and I look forward to hearing the feedback on these topics.
I’m sure everyone has heard at least once, that sugar feeds (or even causes) cancer. Just like all pseudoscience and misinformation, there are nuggets of truth. Unfortunately, when people who aren’t qualified to discuss these topics get ahold of those nuggets, they mischaracterize them. In this case, it is the fact that cancer cells use sugar in metabolic pathways. But that’s pretty much where it ends.
This myth is born from misinterpretation (possibly intentional manipulation) of a phenomenon called the Warburg effect, named after the scientist, Otto Warburg, who characterized it in the 1920s. Before we get into it, let’s clarify:
Sugar does not cause or feed cancer.
All cells utilize sugar as a preferred energy source.
When people think about “sugar” they often think of the white granulated stuff that is in everyone’s pantry. That sugar is sucrose.
But sugar, chemically, refers to carbohydrates with the general formula Cn(H2O)n. Simple sugars are a single unit with formula C₆H₁₂O₆ - this would include glucose and fructose. Sucrose is one fructose and one glucose attached to each other, a disaccharide, C₁₂H₂₂O₁₁. Lactose is also a disaccharide, C₁₂H₂₂O₁₁, consisting of one glucose and one galactose.
Then you have your longer carbohydrate chains, polysaccharides, like starches. While people don’t think of these as “sugars” in the traditional sense, they are repeating units of monosaccharides.
All cells utilize these to produce cellular energy through cellular respiration. Cellular respiration is a series of chemical reactions where glucose is broken down to create the universal cellular energy molecule, ATP (adenosine triphosphate). ATP drives the processes in our body.
The glucose that enters cellular respiration is obtained through digestion of foods we eat, including larger carbohydrates.
Cellular respiration is separated into 2 phases: phase 1 is glycolysis, which breaks glucose into pyruvate and yields 2 units of ATP. Phase 2 includes the citric acid cycle (TCA), followed by oxidative phosphorylation.
Humans need oxygen for survival - we are aerobic organisms. But our cells can produce energy, at least for a limited time, without oxygen - in an anaerobic environment. It’s just not nearly as efficient.
In an anaerobic environment, glycolysis can still occur, but you only get 2 net ATP per glucose molecule. In contrast, in an aerobic environment, pyruvate will enter TCA and oxidative phosphorylation, leading to the synthesis of 30 ATP per glucose molecule.
As you can tell, it is beneficial for cells to complete the full respiration pathway to maximize usable energy: 2 ATP units versus 30 ATP units is a big difference!
So, you’re probably asking, what does this have to do with cancer?
Otto Warburg determined that cancer cells often used glycolysis even when oxygen WAS available.
This is the Warburg effect.
This was counterintuitive. Glycolysis is not efficient for ATP synthesis, and usually only occurs in isolation when oxygen isn’t available for oxidative phosphorylation.
Why would cancer cells use a less efficient process for ATP synthesis?
Cancer cells no longer behave normally and continue to reproduce, even when they have serious errors. Normal cells would be triggered to die when they are defective, but cancer cells ignore those signals. But what this means is that cancer cells are undergoing rapid cell division, which eventually leads to the formation of tumors.
Rapidly dividing cancer cells need to make cellular materials if they want to continue to reproduce.
In order to continue to grow, cancer cells need raw materials (like nucleotides, amino acids, and lipids) needed for rapid growth and proliferation. These materials make up cell walls, proteins, DNA, all of the components of a cell. These materials are created using biosynthesis: taking smaller subunits and stringing them together.
For example, protein synthesis occurs when mRNA is converted into amino acids. Amino acids are linked in specific orders based on the mRNA sequence, and then fold into different shapes based on how the amino acids interact with each other.
Cancer cells preferentially use glucose for biosynthesis instead of ATP synthesis.
As a result, cancer cells may consume glucose more quickly compared to some other cells, so that they can produce those raw materials (like nucleotides, amino acids, and lipids) needed for rapid growth and proliferation.
We will save more of this story for another day!
PET scans aren’t "proof" that sugar feeds cancer.
This Warburg effect - the unique metabolic feature of cancer cells, is utilized for a screening tool called PET scan (Positron Emission Tomography). PET is an imaging test that aids in cancer detection.
PET scans use a radioactive tracer, a glucose analog called fluorodeoxyglucose (FDG) that is injected into the bloodstream. FDG is glucose with a hydroxyl (-OH) replaced with radioactive fluorine (F-18). FDG will be taken up by cells in the body in the same way blood glucose would be.
But the radioactive fluorine decays into oxygen-18 and releases a positron in the process. The positron will bounce around and hit an electron in your body (all atoms, molecules, compounds, have electrons), which causes a reaction called electron-positron annihilation. This annihilation releases energy, specifically in the form of a gamma ray (a high energy photon).
That energy is detected by the PET scanner and the radiation measurements are used to create a composite image of the body. Brighter regions indicate areas that have taken up more of the FDG because those areas are consuming glucose at a faster rate. The more FDG that is taken up, the more has decayed in that area and generated those photons. FDG is used in oncology PET scans because many cancer cells do consume glucose at a faster rate compared to other healthy cell types.
PET scans don’t ONLY highlight cancer cells.
While people spreading misinformation like to claim that PET scans, and the fact that tumors consume higher levels of FDG, is “proof” that sugar feeds cancer. It isn’t.
Remember how I said that all cells use glucose? That applies here too. PET scans will highlight any cells in the imaging region that are consuming higher levels of glucose relative to the rest of the surroundings. That *can* be cancer cells, but it can also be healthy cells and tissues: the brain consumes extremely high levels of glucose, muscles (especially if you’ve recently exercised), liver, spleen, the GI tract, bone marrow (especially in children), and other areas of the body that have injuries, infection, or inflammatory processes going on.
The increased uptake of glucose (or FDG) by cancer cells is simply due to their metabolic demands, not because they are uniquely fueled by sugar. Which brings me to the final point.
Sugar doesn’t selectively FEED cancer.
This is the main misinterpretation of the Warburg effect, PET scans, and even in vitro studies where cancer cells are provided glucose excess in nutrient media.
Yes, some cancer cells consume glucose at a higher rate which helps support those biosynthetic pathways. But glucose consumption isn’t unique to cancer cells. All of your cells utilize glucose. Many healthy tissues and organs consume glucose at high rates as well, as noted above.
Trying to limit “sugar” intake is not only impossible, but doesn’t do anything to slow the spread of cancer, or prevent you from developing cancer in the first place. This persistent myth is a gross oversimplification of complex processes that this piece doesn’t even scratch the surface of.
Not all cancer types preferentially use glycolysis, either.
Otto Warburg was studying cancer 100 years ago. Like in all fields of science, our knowledge accrues over time. And we know a lot more about cancers today, which are hundreds of diseases. While cancers share some hallmarks, they are not all the same - which is why they are also not all treated the same (and why we will never have a universal cure for cancer, probably).
There are many cancers that utilize aerobic cell respiration like melanoma, lymphomas, prostate, ovarian, and some types of lung and renal cancers.
Cancer cells will adapt to use any nutrients they can access.
Alongside fear-mongering about cancer and sugar is the promotion of “low carb” or keto diets to prevent to cure cancer. Hate to break it to everyone, but whatever you consume, cancer cells will use those nutrients.
If you restrict sugars and consume higher levels of proteins and fats? Cancer cells are going to use those as their energy source. Conveniently, metabolic byproducts of proteins and fats can ALSO be shuttled into cellular respiration pathways. Restricting carbohydrate intake has not been demonstrated to reduce cancer progression, prevent cancer, or improve cancer outcomes.
Wellness influencers promote harmful pseudoscience about cancer.
Complex science is manipulated by wellness influencers or alternative practitioners who claim that avoiding sugar will starve cancer. The wellness industry propagates these harmful messages in books, social media content, and even health professionals who push sugar-free diets as a cure for cancer. Not only does this not have evidence, these “alternative” cancer treatments increase risk of poor outcomes, including death (see here for more).
It also goes hand-in-hand with demonizing “sugar” and claiming that any foods containing sugar are inherently unhealthy. It is part of an overarching theme that uses hyperbole: because in excess, sugar (or anything) can cause weight gain and some adverse health effects, therefore, at normal levels, it must also be bad.
This is not true, of course. But it is a successful fear-mongering tactic, especially as it relates to cancer, because the word cancer itself connotes so much fear.
You didn’t get cancer because you ate sugar. And you’re not going to prevent cancer by trying to avoid sugars.
This myth not only blame cancer patients for something out of their control, it is demonstrably false. These claims erode trust in scientific evidence, especially when paired with other messaging geared toward discrediting evidence-based medicine.
This misleads people and spreads fear and confusion. It can lead to harmful consequences such as malnutrition as a result of rigid diets, health anxiety and food fear, refusal to adhere to evidence-based cancer treatments, and interactions with treatments. All of these can impact cancer prognosis and quality of life.
Cancer misinformation is a threat to public health.
It’s long past the time for “politeness” on these topics. Health misinformation is a tangible danger to society. That’s incredibly evident in the cancer space, a category of diseases that are already poorly understood and incredibly difficult to treat. Endorsing, elevating, and legitimizing falsehoods is harmful. Collective effort is needed to combat it. In the case of cancer, truth is a matter of life and death.
Thank you for supporting evidence-based science communication. With outbreaks of preventable diseases, refusal of evidence-based medical interventions, propagation of pseudoscience by prominent public “personalities”, it’s needed now more than ever.
Stay skeptical,
Andrea
“ImmunoLogic” is written by Dr. Andrea Love, PhD - immunologist and microbiologist. She works full-time in life sciences biotech and has had a lifelong passion for closing the science literacy gap and combating pseudoscience and health misinformation as far back as her childhood. This newsletter and her science communication on her social media pages are born from that passion. Follow on Instagram, Threads, Twitter, and Facebook, or support the newsletter by subscribing below:
Perfect timing. I am an oncology RN and just last week I had 2 diff patients with metastatic cancer resist certain foods on their tray because “sugar feeds cancer”. I tried to encourage them both to eat whatever they felt they could keep down and maybe worry less about the ingredients for the moment, pointing out that the research had not linked sugar and cancer in this kind of direct and menacing way. No luck.
If “ Cancer cells preferentially use glucose for biosynthesis instead of ATP synthesis” and consume sugar at a faster rate than healthy cells, could refraining from sugar slow the growth of cancer cells (not cure),
In that context, then could a low sugar diet SUPPORT conventional treatment (not replace it)?