22 April 2014

There is practically no link between nutrition and cancer

An apple a day and other myths

Dmitry Tselikov, CompulentaIf you look through popular literature and especially the Internet, you may get the impression that cancer prevention is primarily related to nutrition.

One source after another glorifies the qualities of "superfoods" rich in antioxidants and other phytochemical compounds, and also advises readers to imitate the diet of Chinese peasants or Paleolithic cavemen.

As George Johnson writes in the New York Times, there is a giant gap between this folklore and science. And you could find out what science says about this in San Diego at the recent conference of the American Association for Cancer Research, which brought together more than 18,500 scientists and other specialists who are not indifferent to the topic. The link between nutrition and cancer has been actively studied for decades, and this time a separate session was devoted to it, as well as several presentations. It turned out that coffee slightly reduces the risk of certain types of cancer, and vitamin D is also useful in this regard. That's all.

At the opening plenary session of the conference, Harvard epidemiologist Walter Willett, who has been studying the link between cancer and food for many years, looked depressed. No matter what they say about other diseases, there is no reason to believe that fruits and vegetables protect against cancer, and fatty foods contribute to it.

We can only say with certainty that cancer has a link with obesity, as well as cardiovascular diseases, type II diabetes, hypertension, stroke and other threats to life. What else? Try not to get carried away with alcohol. Make sure that the nutrition is correct. But in general, the impact of certain products on the risk of cancer is so small that it sinks into a sea of statistical noise.

Scientists did not always adhere to this opinion. In 1997, the World Cancer Research Foundation and the American Institute of Cancer Research published a report as thick as a phone book, claiming that diets rich in fruits and vegetables reduce the risk by more than 20%.

Having studied over four thousand studies, the authors were convinced that green vegetables help prevent lung and stomach cancer. Malignant neoplasms of the colon and rectum, as well as thyroid cancer can be avoided with broccoli, cabbage and Brussels sprouts. Onions, tomatoes, garlic, carrots and citrus fruits also seemed to play an important role.

However, the next report, published in 2007, contained very different conclusions. Some types of products are slightly useful in cancer prevention, but it would be an exaggeration to consider them reliable protection.

The reason for the revision was a more thorough epidemiology. Previous studies were usually "retrospective", that is, they relied on respondents' memories of how they ate in the distant past. The results obtained in this way were often refuted by prospective studies that tracked the health status of large populations in real time.

Simultaneously with the collapse of the hypothesis that the consumption of plant fibers allows you not to be afraid of cancer, the assumption about the danger of fatty foods collapsed. The information that red meat causes colon and rectal cancer is hopelessly outdated. Two meta-analyses published in 2011 came to different conclusions: one found a small effect, and the other found nothing.

Even if hamburgers are really carcinogenic, it's almost not noticeable. One study showed that a 50-year-old man who eats an average of about 130 grams of red meat a day (which is a lot), the chances of acquiring colon and rectal cancer over the next decade increase to 1.71% from 1.28%. In a large population of millions of people, this effect will be noticeable. From the point of view of an individual, there is nothing to worry about.

Attempts to find at least some correlation in the interweaving of variables inevitably lead to the appearance of a mass of contradictory articles. When San Diego had already wrapped up, a paper appeared claiming that there was a link between a high-fat diet and breast cancer.

But even with the most thorough research, it is difficult to take into account all the factors that can distort the result. It is obvious that people who are faithful to fruits and vegetables, as a rule, weigh less, exercise more often and take better care of their health in general. It makes sense to conduct a randomized controlled trial involving two large groups that would adhere to different diets. However, such work is expensive and, in fact, impossible, because it is very difficult to force a person to strictly adhere to a certain diet for at least some time, and it takes years and years to identify the connection of nutrition with cancer.

The conference participants were interested in other things: new types of immunotherapy, the role of chronic inflammation and the endless evasions of cancer cells. Mr. Willett, with his interest in nutrition, seemed like a black sheep. At the banquet organized by the M. D. Anderson Cancer Center, thick slices of roast beef, a rich selection of cheeses and wine were served. Then there was a sumptuous dessert. There were also coffee breaks.

So for today, only two correlations can be considered firmly established: cancer and smoking, cancer and obesity. It is dangerous not to eat fat, but to be fat.

Based on the materials of The New York Times: An Apple a Day, and Other Myths.

For references to the scientific research mentioned here, see the original article – VM.

Portal "Eternal youth" http://vechnayamolodost.ru22.04.2014

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