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Can Sugar Feed Cancer Cells? We Investigate

Sugar makes cancer cells grow faster - studies suggest. But is that really true?

ketogenic diet - Should breast cancer patients avoid sugar?


Sugar allows some cancer cells to grow more quickly – according to certain studies at least. Some doctors, therefore, advise their patients to eliminate foods and drinks that contain sugar from their diets. But is it really beneficial?

In April 2016, doctors diagnosed Mathilda Berger* with breast cancer – more specifically, a “left invasive-ductal carcinoma with at least two tumour centres,” as the 39-year-old writes in her German-language blog, “Living with Breast Cancer.” It was a shock for Berger. But instead of dwelling on the question of “Why?” for a long time, she started to research: Berger wanted to know what she could do to positively influence her breast cancer.

She came across a report online, of a 2013 experiment by Harvard scientist Lewis Cantley. With his team, he was able to prove that breast cancer cells stop growing when they are deprived of sugar – at least in the petri dish.


"Cancer Cells Are Dependent On Sugar"


It has been known for a long time in the world of medicine that tumour cells react to sugar. Perhaps the dependence of cancer cells on glucose (sugar) is related to mitochondria; with their help, health cells absorb fats, proteins and sugar from food, which they then burn to produce energy. However, in cancer cells, the function of the mitochondria often appears to be disrupted. Fats, as well as many proteins, are useless to them.

Cancer cells don’t burn the sugar but ferment it instead. This results in lactic acid, which makes it easier for them to penetrate the surrounding tissue. What’s more, the activity of the immune cells is inhibited. “Cancer cells are dependent on sugar,” concludes Cantley in an interview with the ARD broadcasting service in Germany. “Without it, they die.” 

Which is why Berger asked herself: Would it be best for me to cut sweet food and drinks out of my diet? The aim of one such diet – the ketogenic diet – is so-called “ketosis:” Long-term deprivation of sugar should bring about a change to the body’s metabolism. From then on, the cells should only gain their energy from fats and proteins, instead of sugar. The result: a tumour “starves” – at least in theory.

But dietitians at the Tumour Centre in Munich (Tumorzentrums München, or TZM) are not convinced by this approach. So far, there isn’t sufficient proof of the positive effects of the ketogenic diet, according to the TZM. Shutting down human cell cultures is “dubious” in their view. As such, the ketogenic diet is not to be recommended to people with cancer.

Professor Jutta Hübner, scientist and member of the Cancer Prevention Centre workgroup of the German Cancer Society, agrees: “At this point in time there is no scientific study that proves such a diet can prevent or reduce the growth and metastasis of tumours in people". 

(Editor’s note: this refers to the use of a low-carbohydrate or ketogenic diet.)

Cancer cells and sugar - starving cancer cells with a ketogenic diet

From Hübner’s point of view, the theory is fundamentally questionable: “In fact, cancer patients shouldn’t allow their blood sugar level to sink too low – only as low as that of people in good health.”

Why is that? “If the body doesn’t receive carbohydrates for a long period, it produces glucagon and other stress hormones,” explains the researcher. “This initiates the regeneration of sugar, especially in the liver.” 

Therefore, even when fasting, the body is never completely free of sugar. 

Hübner points out another fact as well: “If you deprive cancer cells of sugar,” she explains, “many cancer cells actually change their metabolism and grow more slowly.” However, over time they learn to metabolise proteins and fats and then grow even faster. Some cancer cells even mutate into malignant stem cells.

However, she does agree with the proponents of the ketogenic diet on one point: Rapidly available carbohydrates that cause the blood sugar level to shoot up can, in fact, encourage the growth of tumours. She, therefore, recommends that cancer patients eat a balanced diet and consume refined sugar in moderation. 

Adjust Your Diet Before Chemotherapy But Enjoy Your Food

That’s how Mathilda Berger sees it. Inspired by her research and on the recommendation of her doctors, she adjusted her diet before her chemotherapy started – also to avoid (severe) nausea during treatment.

She gave up food with added sugar and removed fast-acting carbohydrates, such as pasta and chocolate, from her meal plan. 

Her nutrition, therefore, conformed somewhat to the ketogenic diet. But only partly. Because the blogger knows: “Complex carbohydrates and fibre belong in a healthy diet.” She discussed this in detail with a dietitian at the University Hospital in Germany. Besides, Berger is a food lover.

When she wants some ice cream or cake, she goes for it – and then goes for a walk or exercises, because moving our bodies also lowers blood sugar levels.

*Mathilda Berger” is a pseudonym.



Amoena Claudia Kaltenecker

Claudia Kaltenecker

Illustrations: Yulia She/Shutterstock/ Sandy Braun