Food and diet

5:2 diet style an 'immune booster,' study finds

“Fasting for at least two days regenerates immune systems damaged by ageing or cancer treatment, research has shown,” the Daily Express reports. However, the study that is being reported on only involved mice, not humans.

Prolonged or intermittent fasting has become an increasingly popular strategy to achieve weight loss. This has been demonstrated through the incredibly popular 5:2 diet, where participants eat normally for five days a week and then fast for the remaining two.

There have been reports that the 5:2 diet can lead to weight loss for some people, with others claiming that fasting can boost immune function and prevent chronic diseases.

In this study, which used only mice, the researchers aimed to see whether prolonged fasting could reverse the toxic effects of chemotherapy – specifically, damage to white blood cells and bone marrow activity, which leaves the body weakened and vulnerable to infection.

Researchers found that mice fasting for two to five days before being given chemotherapy showed a faster recovery in terms of their white blood cell count. A later-stage clinical trial in humans is reported to be underway.

It is extremely important to stress that if you are undergoing chemotherapy treatment, you should not make any kind of radical changes to your diet unless advised to by your doctor. Doing so could make you vulnerable to complications.

Where did the story come from?

The study was carried out by researchers from the University of Southern California, Ohio University and the University of Palermo, in Italy. The study was supported by the National Institutes of Health and Aging and was published in the peer-reviewed science journal Cell. It has been published on an open-access basis, so it is free to read online.

The Daily Telegraph’s reporting of the study was accurate and included discussion from experts, who said that while the findings may have relevance for people receiving cancer treatment, further study is needed, and prolonged fasting should only be considered under the guidance of a doctor. As the Professor of Regenerative Medicine at UCL, Chris Mason, suggests: “The most sensible way forward would be to synthesise this effect with drugs. I am not sure fasting is the best idea. People are better eating on a regular basis.”

The Daily Express’s coverage, while not inaccurate, was not as clear as it should be. It is not until the last part of the article that you realise the study involved mice, not humans.

What kind of research was this?

This was a scientific study using mice, which aimed to look at the effect prolonged fasting might have on reversing the toxic effects of chemotherapy.

This included how it affected bone marrow regeneration and circulating white blood cells – key components of the body’s immune system.

The researchers explain how immune system defects are central to the ageing process and are associated with a range of diseases. One of the effects of chemotherapy is DNA damage and cell death, to both circulating blood cells and to stem cells of the bone marrow, which are responsible for producing new blood cells.

This leads to reduced numbers of red blood cells (which carry oxygen), platelets (which help blood to clot) and white blood cells (which make up the body’s immune system), leaving the body weakened and vulnerable to infection.

All of this can result in a wide range of side effects for people undergoing chemotherapy.

The authors state that prolonged fasting for two to five days activates cellular pathways in mice and humans, which enhance the resistance of cells to toxins, such as chemotherapy. Previous studies in mice have found that prolonged fasting leads to this protective effect, by reducing levels of insulin-like growth factor-1 (IGF-1) – a protein involved in growth and development, with a similar function to insulin.

The theory is that the reduction of IGF-1 resulting from prolonged fasting may allow regeneration of stem cells in the bone marrow, and so help to reverse the toxic effects of chemotherapy.

What did the research involve?

Mice were divided into two groups who were either fed or fasted prior to being injected with chemotherapy drugs for two weeks. The researchers looked at white blood cell counts during and after chemotherapy treatment, and also assessed DNA damage in circulating blood cells and bone marrow cells.

As their previous study had shown that prolonged fasting leads to a reduction in IGF-1 levels, and they believed that this was responsible for the protection against chemotherapy, they also looked at what would happen when mice genetically engineered to have IGF-1 deficiency were given chemotherapy without having fasted.

What were the basic results?

The researchers found that multiple cycles of prolonged fasting protected mice from some of the toxic effects of chemotherapy, reducing DNA damage to both circulating white blood cells and bone marrow stem cells. It also led to the regeneration of bone marrow stem cells. Mice who were given chemotherapy but fed as normal showed prolonged white blood cell depletion, while mice who had fasted beforehand saw their white blood cell count return to normal levels at a faster rate.

As expected, they found that using mice genetically engineered to have IGF-1 deficiency – replicating the effects of prolonged fasting – also showed faster recovery of their bone marrow stem cells. This confirmed that the effect on bone marrow stem cells was probably being mediated by a reduction in IGF-1 levels. Reduction of IGF-1 signalling seemed to promote the renewal of bone marrow stem cells.

How did the researchers interpret the results?

The study authors concluded that their results “indicate that cycles of an extreme dietary intervention represent a powerful mean[s] to modulate key regulators of cellular protection and tissue regeneration, but also provide a potential therapy to reverse or alleviate the immunosuppression caused by chemotherapy treatment and ageing”.


This scientific study suggests that multiple cycles of prolonged fasting may be able to reverse some of the toxic effects of chemotherapy in mice, by causing the regeneration of stem cells in bone marrow.

This allowed white blood cell counts to return to normal much faster after chemotherapy, compared to mice that were allowed to eat normally.

The study researchers indicated very early-stage study in humans (not appraised here), which found that fasting for 72 hours, rather than 24 hours, in combination with chemotherapy reduced some of the toxic effects of chemotherapy, in line with the findings in mice.

However, the study’s authors acknowledge that these results are very tentative and will need to be confirmed in larger, more robust, human studies.

phase 2 randomised control trial is said to be underway. 

Based on this study alone, it can be stated that people receiving cancer treatment, including chemotherapy, should not fast for extended periods of time without fully consulting a health professional, as this could be damaging to their health in other ways. Appropriate nutrition is very important for people with cancer, during treatment and when recovering from treatment. You should not make any significant changes to your diet without first seeking the advice and guidance of the health professionals treating you.

NHS Attribution