Cancer: The Carbohydrate Connection

We’ve known about this for a hundred years. Time to act.

In 1924, German medical doctor and scientist Otto Heinrich Warburg made a discovery that was to potentially revolutionise our understanding of cancer. His astonishing breakthrough, that was to later earn him a Nobel Prize in physiology, could have — should have — changed the course of cancer prevention and treatment. But it didn’t. It wasn’t about drugs.

When Warburg studied the way tumours use fuel as energy, he discovered that most cancer cells burn glucose to drive their growth and multiplication.

Normal, healthy cells generate energy (adenosine triphosphate, or ATP) anaerobically, that is, without the presence of oxygen. Cancer cells, on the other hand, generate their energy by fermenting dietary glucose to lactate, in the presence of oxygen. Fermentation of glucose to lactate plays an important role in the development of cancer, as Warburg demonstrated. This is called “aerobic glycolysis”, although it is now often referred to as the “Warburg effect”.

Aerobic glycolysis is a method that cancer cells appear to favour: they just love sugar. Warburg demonstrated how glucose uptake in tumour cells is 47%-70% compared to 2%-18% in normal cells.

“Due to the Warburg effect, glucose in dietary carbohydrates acts as a primary metabolic fuel for many tumors.”

This consumption of large quantities of glucose allows cancer cells to grow and divide in an uncontrolled manner.

In a 1966 lecture to the meeting of Nobel Laureates at Lindau, Bavaria, Otto Warburg commented:

“Cancer, above all other diseases, has countless secondary causes. But, even for cancer, there is only one prime cause. Summarized in a few words, the prime cause of cancer is the replacement of the respiration of oxygen in normal body cells by a fermentation of sugar.”

The Diet Connection

Glucose is a sugar that comes from carbohydrate in the diet.

If carbohydrates — sugars — provide the fuel that tumours need to grow, does that mean that carbohydrates cause cancer? Not necessarily, though clearly there is a strong case, and surely plenty of motivation, for more in-depth research.

Or so you’d expect: astonishingly, there isn’t a great deal. Having said that, there are two dietary strategies that have been subjected to some scrutiny, and that are loaded with potential. These are calorie restriction and/or fasting, and ketogenic diets.

Calorie restriction and fasting

Calorie restriction (CR) lowers circulating glucose and insulin levels. It is a potential cancer suppression method, first introduced in 1914 and used in studies of brain, prostate and breast tumours. Because CR “shuts off” the energy supply to the tumour, it is believed to have “great potential as a cancer therapy”.

CR is not an alternative therapy; it is considered an adjunct therapy, to be used alongside traditional chemotherapy or radiation.

Fasting also leads to glucose deprivation, meaning that cancer cells are cut off from their source of fuel. Compared to calorie restriction, fasting results in a more profound decrease in insulin and blood glucose (50% compared to 25%). Clinical studies suggest that fasting, as an adjunct therapy to chemotherapy, may “mitigate the toxicity of chemotherapy”.

Keto and cancer

Another potential dietary adjunct is the high-fat, low-carbohydrate ketogenic diet. Like fasting and calorie restriction, the ketogenic diet reduces glucose in the blood, lowering insulin. Instead of burning glucose, the body switches to burning ketone bodies, depriving the cancer cells of their energy source. Ketogenic diets “are therefore attractive for long-term application during cancer treatment”.

Limiting sugar intake, as much as possible, may be a good way to protect against developing cancer in the first place, because high dietary sugar intake is associated with greater risk. The sugar intake of 101,279 participants from the French NutriNet-Santé prospective cohort study (2009–2019) found that “Total sugar intake was associated with higher overall cancer risk”, in particular risk of breast cancer.

Fructose — fruit sugar — has been the subject of particular scrutiny, having been identified as a significant factor in the development of obesity and metabolic syndrome. Like glucose, fructose metabolism produces lactate. It promotes the Warburg effect, increasing aerobic glycolysis and leading researchers to suggest that “Blocking fructose metabolism may be a novel approach for the prevention and treatment of cancer.”

Indeed, fructose and glucose have been shown, in cultured cancer cells, to have the same effect on cell proliferation.

Meanwhile…

As the evidence for the case against sugar continues to mount, so too does the vast quantity of sugar consumed today.

In 2015, the World Health Organization issued guidelines that sugar should make up no more than 10% of total daily calorie intake. The WHO added that better still, aim for no more than 5%, or around 25 grams (6 teaspoons) maximum per day.

By 2016, the US had the highest per capita consumption of sugar in the world, at roughly 126 grams a day. We do comparatively well in the UK, with an average per capita consumption of “only” 93.2 grams a day.

Just one can of soda may contain around 10 teaspoons — 40 grams — of added sugar. The sugar now most favoured by the food industry is super-sweet, high-fructose corn syrup (HFCS). HFCS is corn syrup that has undergone a process to convert some of its glucose into fructose. The result is an exceptionally and intensely sweet product.

HFCS is now the most common sweetener in soft drinks in the US, where it has come to replace ordinary sugar in all processed food, mainly because it is much more cost-effective to do so. It is ubiquitous in drinks, bread, cereals, cereal bars, and just about anything where ordinary table sugar might once have made an appearance.

Despite the knowledge so far accumulated, since the early 1940s there has been only “sporadic interest” in using dietary approaches such as the ketogenic diet as a cancer treatment. Case reports with favourable results are occasionally published. But there is hope: in 2020 there were 62 ongoing trials evaluating the value of low carbohydrate diets, including the ketogenic diet, as potential adjuvant cancer therapies. It’s looking promising, because:

“Preliminary reports indicate that these patients were able to continue the KD therapy for over 3 months and showed improvement, including stable physical condition, tumor shrinkage, and/or slowed tumor growth”

It’s taken almost a hundred years since Otto Warburg’s breakthrough discovery for scientists to acknowledge that “it is reasonable to hypothesize that higher sugar intake may increase cancer risk.”

But you can reduce your risk right now.

Readers of my articles will know I’m not exactly a fan of sugar. For information of other ways that it is so detrimental to your health, see:

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