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Diet myths and cancer

No. 42 | 12/10/2016 | by jg / Koh

Fasting starves tumors, foregoing sugar slows down cancer growth, alkaline foods protect from cancer: Many special diets and dietary patterns supposedly have the potential to prevent cancer or an existing disease from spreading in the body. Do these theories withstand scientific scrutiny? An interview with Dr. Susanne Weg-Remers, head of DKFZ's Cancer Information Service (KID), on World Food Day on October 16.

Susanne Weg-Remers
© DKFZ/Tobias Schwerdt

Dr. Weg-Remers, many people who have been diagnosed with cancer are concerned about their diet. In most cases, this is because they hope that certain foods – or avoiding them – can prevent the disease from recurring or spreading. A multitude of recommendations of this kind are floating around on the Internet and many callers at the Cancer Information Service have questions about this topic.

Yes, that's right. For example, people frequently ask whether eating sugar increases tumor growth. There are in fact observations indicating that the energy metabolism of cancer cells differs from normal cells. But it has also become clear that this does not hold true for all cells, nor for all types of cancer or disease situations. Therefore, it is not necessary to completely abstain from sugar. Current dietary guidelines for cancer patients even clearly state that the health benefits of a diet that entirely foregoes sugar and possibly also other carbohydrates have not been proven to date.

Is it possible to "starve" cancer?

Foregoing carbohydrates altogether or fasting is usually not beneficial for cancer patients. Most of them cannot afford losing a lot of weight. However, cancer patients who are overweight despite their disease may consider eating a diet that is lower in carbohydrates, but they should do so only under medical guidance.

Coffee has also often been suspected to promote cancer.

Coffee appears to be better than its reputation, though. At least, no harmful effect has been proven so far. On the contrary, studies have revealed first indications of a protective effect, because coffee contains many important substances that are also found in fruit and vegetables. However, people who are being treated for cancer may be well advised to ask their doctors whether they would expect interactions between coffee and the medications there are taking.

De-acidifying with alkaline foods, detoxifying with detox smoothies, body cleansing with juices or teas – these are other key words often heard after cancer treatment.

Up until now, there is no scientific proof that cancer patients need detoxifying, de-acidifying or "removing" toxins. Even after stressful treatments such as chemotherapy, the body is able to detoxify itself without any help from outside. Most chemotherapy drugs are excreted within a few hours or days by the intestine and the kidneys. And as to "body cleansing": Many hypotheses behind this idea are no longer tenable today. The theories, many of which are centuries old, no longer agree with what we know now about human metabolism and the course of diseases such as cancer. I am afraid many of these offers that cancer patients come across, for example, on the Internet are purely commercial.

Are there any special diets that can be recommended in good conscience for cancer patients?

There are no studies that clearly prove the effectiveness of special cancer diets. What we basically know today is that any diet that lacks in variety is rather more harmful than healthful. This also holds true for so-called superfoods; these are foods that are supposed to have a special positive effect on health – such as chia seeds, matcha tea or beets.

When assessing special dietary concepts I recommend applying a differentiated perspective that neither demonizes nor idealizes. Instead of betting on a special diet or superfoods, it is more recommendable to eat a diet that is as varied and well-balanced as possible. If there is a danger of malnutrition caused by the disease, cancer patients may need a medically supervised dietary treatment.

The Cancer Information Service (KID) is available daily from 8 a.m. to 8 p.m. at 0800 420 30 40 (toll-free within Germany).

With more than 3,000 employees, the German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) is Germany’s largest biomedical research institute. DKFZ scientists identify cancer risk factors, investigate how cancer progresses and develop new cancer prevention strategies. They are also developing new methods to diagnose tumors more precisely and treat cancer patients more successfully. The DKFZ's Cancer Information Service (KID) provides patients, interested citizens and experts with individual answers to questions relating to cancer.

To transfer promising approaches from cancer research to the clinic and thus improve the prognosis of cancer patients, the DKFZ cooperates with excellent research institutions and university hospitals throughout Germany:

  • National Center for Tumor Diseases (NCT, 6 sites)
  • German Cancer Consortium (DKTK, 8 sites)
  • Hopp Children's Cancer Center (KiTZ) Heidelberg
  • Helmholtz Institute for Translational Oncology (HI-TRON Mainz) - A Helmholtz Institute of the DKFZ
  • DKFZ-Hector Cancer Institute at the University Medical Center Mannheim
  • National Cancer Prevention Center (jointly with German Cancer Aid)
The DKFZ is 90 percent financed by the Federal Ministry of Education and Research and 10 percent by the state of Baden-Württemberg. The DKFZ is a member of the Helmholtz Association of German Research Centers.


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