The gold standard treatment for cancer in the last few decades has been a combination of surgery – to remove tumours – and chemotherapy and radiotherapy – to kill cancer cells. With the progress of personalised medicine, where identifying specific mutations in the tumour guides treatment selection, there has been increasing success in survival rates.
But there has been little improvement in reducing side effects on healthy cells caused by chemotherapy, which also limit the dosage that can be administered.
Over the last two decades, research in animals has shown restricting calories – with alternating periods of fasting and feeding – promotes protection mechanisms for healthy cells, while increasing white blood cells that kill cancer cells.
A 2008 study showed mice with neuroblastoma, a common childhood cancer, that had only water for two days before receiving a large dose of chemotherapy, experienced less or no side effects compared to mice fed normally. In another study, tumour cells were killed more efficiently in mice who weren’t fed than in those that were.
Since then, further animal studies and early trials in humans confirmed short-term fasting prior to, and after, chemotherapy treatment reduced side effects. It also protected healthy cells from the toxicity of the drug, while killing cancerous ones.
So does this mean we can use fasting to help with cancer treatment?
Glucose and cancer
Cancerous cells are known to rely on glucose, a type of sugar, for their energy metabolism, rapid growth, and resistance to chemotherapy.
That cancer cells thrive on glucose was first shown by German physiologist Otto Warburg in the 1950s. He also showed they were unable to use fatty acids as efficiently for energy, or at all. This idea of cancer being a disease reliant on rapid glucose metabolism, has reemerged recently.
Under total fasting conditions, where someone only has water, the body initially uses carbohydrate stores, called glycogen, to maintain blood glucose levels, and for cellular energy production. When these stores are depleted, protein from muscle is used to produce new glucose, and fat stores start to be used for energy production.
Body cells that would normally use glucose as their main energy source have the ability to gradually switch to a different fuel: a product of fat metabolism called ketone bodies. This is to spare muscle mass so it is not used too much to make new glucose.