Keto diet may slow cancer tumour growth in mice – but not without potentially deadly consequences

The ketogenic (keto) diet has been popular in recent years among people looking to lose weight and keep fit. But what many people don’t realise is that this low carb, high-fat diet has actually been used for centuries in the treatment of medical maladies, such as epilepsy. More recently, researchers have been investigating its use alongside chemotherapy to improve remission and survival in patients with advanced metastatic cancers.

A recently published study in mice has now shown that the keto diet may also have use in treating tumours. But while the diet appeared to slow the tumour growth in mice with colorectal and pancreatic cancers, it was also shown to accelerate the onset of cachexia – a severe wasting disease thought to cause 30% of all cancer-related deaths.

To conduct their study, the authors selected two types of mice that were predisposed to cachexia. They then transplanted half of them with colorectal cancer and induced pancreatic cancer in the other half. The mice were then allocated into two groups: one group was fed a standard diet while the other group was fed a high-fat, low carb keto diet.

Over the course of the next month, the investigators found that mice on the keto diet showed slower tumour growth than the mice fed a standard diet. However, it also appeared that the keto diet was associated with shorter survival times due to the faster onset of cachexia.

Keto and cancer

The reason the ketogenic diet works to slow the growth of tumours is down to the way in which cancer cells metabolise their “food” compared to normal, healthy cells.

All the cells in our bodies get their energy from glucose (sugar) first and foremost, and then from fats. Since cancer cells grow quickly, they have much higher energy needs – so they rely solely on glucose for energy.

Glucose is released from the carbohydrates we’ve eaten as they’re broken down in our bodies. But since the keto diet has a very low carbohydrate intake, it’s thought that this “starves” the cancer cells of the energy they need to grow. This is what the authors were able to demonstrate in their study.

Keto also kick-starts a process called lipid peroxidation, which causes the body to use fats for the energy it needs instead. However, this process also creates a number of highly reactive molecules as a by-product which need to be cleared from the body before they cause further cell damage.

A digital illustration of a cancer cell.
Cancer cells have higher energy needs.
Crevis/ Shutterstock

Since the mice’s cells lacked an adequate energy supply to quickly remove these highly reactive molecules, this led to an increase of a molecule called GDF-15 which suppressed their appetite and contributed to their weight loss.

The researchers also found that the keto diet impaired the production of corticosteroids – naturally-occurring hormones which help reduce inflammation and regulate the immune system. This accelerated the onset of cachexia in the mice, shortening their overall survival.

Interestingly, when the researchers treated the mice with an injection of dexamethasone – a corticosteroid drug that counteracts the stress hormone cortisol and is often used to treat various cancer-related conditions, such as anemia – they were able to delay the onset of cachexia and improve their overall survival.

Cancer treatment

Although it’s tempting to draw conclusions from this research, it’s also important to bear a few things in mind.

First, this study was performed in mice – and of course, we aren’t mice. It’s imperative that further research be carried out to see whether the keto diet has a similar effect in humans – and crucially, whether treatment with dexamethasone delays the onset of cachexia in humans, too. At the moment, there are a number of ongoing trials and some emerging evidence suggesting the keto diet has beneficial effects on many types of cancer.

Second, patients who follow a keto diet will experience different benefits depending on the stage of their cancer. For example, studies in cells have shown fasting or following the keto diet while undergoing chemotherapy may improve how responsive the cancer is to chemotherapy – while also reducing damage to nearby healthy tissues.

This is because fasting (and keto) act like a “magic shield”, protecting healthy cells from chemotherapy-induced damage.

Fasting shuts down all non-essential processes, including metabolism. However, cancer cells ignore this message and continue growing. Chemotherapy targets rapidly growing cells – and so in a fasted state, it will target the cancer cells instead, leaving healthy cells safe.

Although this latest study demonstrates that the keto diet may also have the harmful effect of accelerating cachexia in mice, several studies looking at the effect of a keto diet on pancreatic cancer actually find keto protects against muscle loss.

These differing results may be down to the methods used in each of these studies, with some experiments being conducted in cells, and others in mice. But given these contradictory findings, it will be important for more detailed investigations to be done.

While evidence suggests keto may have benefits for slowing cancer growth, less is known about any adverse effects it may have (such as accelerating cachexia). Given there’s still so much we don’t know, it’s advised that patients undergoing cancer treatment speak with their medical practitioner about any diet changes they may be planning to make.

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