Refraining from eating during chemotherapy: This sounds completely crazy, but it is currently being intensively investigated. The first very positive effects are emerging.
For decades it was a no-go: cancer patients should under no circumstances fast in order not to weaken themselves further. However, recent study results could partially shake this belief. We spoke to the doctor Daniela Koppold, founding member and lecturer of the Academy for Integrative Fasting, about the effect of not eating around chemotherapy on its effects, how the new perspective came about and why it is not an option to start fasting on your own.
Miss Dr. Koppold, how did researchers like you come to investigate the effects of fasting during chemotherapy?
First of all, the idea itself is not new. As early as the beginning of the 20th century, fasting clinics were set up in which, among other things, cancer patients were treated. However, the drug therapies back then were nowhere near as effective as they are today, patients had poorer prognoses and often had a very low body weight during the course of the disease. The risk of death increased with low food intake. That is why fasting was considered taboo, one has for the time being said goodbye to the topic and concentrated on the further development of diagnostics and clinical therapies. Fortunately, there has been tremendous progress.
Today we see those affected in much earlier stages of the disease, thanks to early detection programs and imaging methods, we take a closer look and can start effective therapies early on. Weight loss is usually only a problem in the late stages of cancer, when the tumor consumes many resources. In the case of common tumor diseases such as breast cancer, however, patients are often overweight at the time of diagnosis.
How did the accompanying fasting therapy regain consciousness?
Around 15 years ago, researchers in the USA discovered that in many cases – not all – tumor growth is related to metabolic processes and, above all, the release of the hormone insulin. This hormone is produced to keep blood sugar levels constant. But it also promotes the production of growth hormones, such as IGF-1. This is important for development in childhood and adolescence. In later years, however, excess amounts can promote tumor growth. In our largely overfed society, many people have levels of IGF-1 that are too high.
So the idea of fasting is: eating less, less insulin secretion – and therefore lower growth hormone levels?
In principle yes. In animal experiments, it was found that mice that fasted during chemotherapy not only had significantly lower levels of IGF-1. The tumor could also be fought much faster and better. The effects of chemotherapy increased while side effects decreased. Apparently, the metabolic processes in the healthy cells changed in the nutrient-poor period in such a way that internal recycling programs were initiated. However, during these repair phases, healthy cells do not interact as much with the outside world, so they suffer less damage from chemotherapy. Tumor cells, on the other hand, are usually not particularly adaptable, but absorb even more chemotherapeutic agents during the fasting period.
Really impressive. But animal experiments cannot be extrapolated directly to humans.
That’s right. There was great concern about starting human trials. Data collection in this area is fundamentally difficult. In addition, not all chemotherapy regimens are suitable for concomitant fasting, for example if the drugs have to be administered for several weeks at a time, as is often the case with brain tumors. That would lead to critical weight loss. In fact, there were enough brave people with cancer, whose treatment regimen and physical condition suited them, who decided to try this supportive measure during their chemotherapy. They received chemotherapy on one or more days and then had a treatment break of several weeks. During the chemo, they agreed to try supportive fasting under professional supervision.
Wasn’t there a big risk of harming patients?
First of all, of course, after detailed examinations and discussions, it had to be determined whether the person concerned had the appropriate constitution for fasting, i.e. a sufficient body weight and stable cardiovascular conditions. If you are already in the phase of muscle breakdown, you should never fast. Appropriate fasting programs around the time of chemotherapy have been developed for those who are interested in a stable condition.
Cancer progression depends on many factors. Which effects can specifically be attributed to fasting?
Just the biochemical markers like lower insulin and IGF-1 levels and the reduced extent of toxic cell damage in healthy cells. Additionally, in our own pilot study, in which we examined 34 breast cancer patients, participants reported reduced nausea, less tiredness and fatigue as positive side effects of fasting. The effect on a psychological level should not be underestimated either. The thought “I can contribute something by fasting myself, I’m not at the mercy of helplessness” makes a tremendous difference to many and provides at least some sense of control in this dangerous, frightening situation in life.
There were only 34 patients – could the effects be coincidence?
Of course, we are still at the beginning and need to verify the observations. A study with 120 participants has been running since 2020, in which we use two groups to compare whether short-term fasting during chemotherapy is more effective than a short-term plant-based diet with a reduction in refined carbohydrates. Unfortunately, financing large studies with thousands of patients is very difficult because there is not much money to be made from the topic of fasting.
Does fasting for cancer patients during chemotherapy really mean giving up solid food completely?
There are different approaches. In our study, the breast cancer patients abstained from solid food for about 36 hours before the start of chemotherapy in each treatment cycle, and only drank vegetable juices or boiled oat and flaxseed broth after a previous day of relief. Fruit juices are not suitable because the sugar content is often very high. The participants maintained this juice and juice fasting for about 24 hours after the end of the treatment. The total duration was around 60 hours.
In other model projects, some of the test subjects also eat small amounts of solid food such as kale chips, olives or nuts. The daily amount of energy ranges between 150 and 500 kilocalories, with a lower nutritional value appearing to be associated with better effects. However, I can only strongly advise those affected not to start fasting on their own, no matter in what form. What is best for this one person should definitely be discussed and accompanied by a doctor.
Fasting does not appear in the so-called guidelines, the recognized recommendations for complementary medicine in cancer. Why not?
On the one hand, because large-scale studies and thus sufficient evidence are lacking. On the other hand, because many connections are still unclear, for example when exactly the right time for fasting has come in the course of therapy. In addition, in the field of drug treatment, there is a tendency to move away from toxic chemotherapeutic agents, towards immune-stimulating drugs such as immune checkpoint inhibitors, or to develop small-molecule therapies that attack cancer cells in a targeted manner. How fasting interacts with this has not yet been studied.
First hyped, then condemned – that was already the case with the ketogenic diet for cancer. Will this happen again?
I don’t assume so. With the ketogenic diet, which is quite complicated to implement, the body should be offered as little sugar as possible, but a lot of fat. The liver can then not burn glucose and instead has to break down fats and convert them into so-called ketone bodies. In my opinion, however, the high fat content is hardly manageable, especially in cancer therapy, which is often accompanied by nausea. When fasting, on the other hand, patients tell me that by briefly abstaining from solid food, they do not mentally associate certain foods with nausea and thus do not develop disgust.
Your prognosis for the future?
Fasting is certainly not a panacea against cancer and is not an option for everyone affected. There are also types of tumors that get along well with fasting and adapt, so you can’t do anything about it. I think further basic research, such as cell analyzes of individual types of cancer, will show which tumor cells respond to fasting. In addition, we should continue to look for alternative nutritional methods that reduce growth factors for people whose life situation does not permit fasting. This could be a targeted reduction in refined sugar, white flour and animal fats. Ideally, such nutritional concepts could prevent many types of cancer altogether. This still requires a lot of effort – and financial support for large studies, for example from sponsors who are interested in the topic.
dr Daniela Koppoldspecialist in general medicine, researches at the Immanuel Hospital Berlin in the department of naturopathy and at the Charité, among other things on the effects of fasting during cancer therapy.