Ask the expert: does sugar feed cancer?

Cubes of sugar on a spoon: does sugar feed cancer?

Isobel Bandurek, World Cancer Research Fund’s Research Interpretation Manager and registered dietitian, answers this commonly asked question.

What’s the hype and who is Otto Warburg?

All cells need fuel for energy. The primary fuel is a simple sugar, glucose, which is processed by cells to release energy. Usually in cells that have plenty of oxygen, this happens in three stages – glycolysis, the Krebs cycle, and oxidative phosphorylation. In cancer cells, however, that turns out not to be the case.

In the 1920s, a German scientist called Otto Warburg and his team conducted experiments and found that cancer cells tend to preferentially metabolise glucose via glycolysis only, rather than through all three stages. This usually only happens when there isn’t enough oxygen available.

As a consequence, cancer cells use up a lot of glucose and this has since been called the ‘Warburg effect’. In fact, the ‘Warburg effect’ is the basis for imaging many tumours – PET scans detect a specially labelled form of glucose which will be more concentrated in the tumour compared to healthy cells. It isn’t clear exactly why cancer cells do this but it seems likely that it has advantages in ensuring sufficient building blocks are available for rapidly dividing cells.

This research earned Otto Warburg a Nobel prize, and interest in the biochemistry of sugar and cancer continues to this day. More recent avenues of research have looked into using diet therapy to ‘starve’ cancer cells of energy. By removing dietary sources of glucose (either as simple sugars or in the form of carbohydrates) it is suggested that cancer cells would not be able to fuel growth and replication, and so would not survive, even though the body is able to produce glucose for metabolism in the absence of dietary sources.

Is there evidence to back it up?

Most studies in this area have focused on the ketogenic diet. This diet restricts intake of sugar and carbohydrates to very low levels, which leads the body to switch its main form of metabolism.

A recent review which systematically identified and assessed all the available studies on the ketogenic diet and people living with cancer found that overall there was not enough high-quality research.1

Some studies looked into the effect of a ketogenic diet on the tumour itself. The results were mixed, with some reporting remission, some reporting no change and some reporting progression. Mixed results were also reported regarding survival from cancer.

The variability in results may be due to the small sample sizes of the studies, the differences in the exact make-up of the ketogenic diet prescribed, or the level to which participants in the studies adhered to the diet.

Weight loss in patients following the ketogenic diet was also commonly reported. This is potentially a problem as research shows that malnutrition (of which weight loss is a component) is associated with poorer outcomes for cancer patients.2

So what’s the bottom line?

With the currently available research, it is not possible to draw firm conclusions about the potential effects of following a ketogenic diet while you have cancer.

There are also many details yet to be understood. For example, does a ketogenic diet have the same effect on all cancers? Do tumours with different genetic markers respond differently to a ketogenic diet? Is there an optimum make-up of the ketogenic diet?

More high-quality evidence is needed in this area before recommendations can be made.

Anyone living with cancer currently should seek advice and support from their oncology team before making dietary changes. It is also important to continue taking prescribed medication as instructed by your doctor.

Eat well during cancer

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1Sremanakova J et al. A systematic review of the use of ketogenic diets in adult patients with cancer. 2018.

2Arends J et al. ESPEN expert group recommendations for action against cancer-related malnutrition. 2017.

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