Preventing obesity – preventing cancer!

Professor Kaaks, in the 2002 Handbook of Cancer Prevention the IARC experts already revealed that post-menopausal breast cancer, cancers of the colon and rectum, endometrial carcinoma, esophagus cancer and renal cell carcinoma are significantly less common in people with normal body weight than they are in obese people. What new findings have now been included in the current edition?

First, we have been able to fully confirm the results published in 2002. In addition, we have found a statistically proven rise in the risk for a number of other cancers. These include, for example, hepatic and pancreatic cancers, ovarian cancer and multiple myeloma as well as adenocarcinoma in the upper part of the stomach called cardia. On the whole, the data from the studies that we evaluated suggest a link between dose and effect: The more severe obesity is, the higher the chances for cancer get.

Can you indicate a dimension? What is the percentage by which the number of newly diagnosed cancer cases could be reduced if nobody exceeded normal body weight?

According to international estimates, the risk share is slightly more than five percent for economically highly developed countries. However, it should be noted that in some cancer types such as cancers of the endometrium and of the esophagus, almost 50 percent of all cases is caused by obesity. And the number of people who are affected will continue to rise, because people around the world are still gaining weight.*

Does being overweight in childhood also play a role?

There are only very few studies that address the link between being overweight in childhood and cancer risk in later life. Therefore, we do not have sufficient data to answer this question. But: overweight children often grow into overweight adults!

Reports state that belly fat, which is located between organs, is the main culprit that raises the chances for cancer. However, the IARC publication refers to Body Mass Index (BMI)**.

The vast majority of studies that we evaluated are based on BMI. Therefore, we had to use this value for pragmatic reasons, in order to be able to compare the studies among each other. But particularly in men, obesity is almost always identical with belly fat, so we can say: high BMI equals fat belly. Therefore, BMI is quite a useful indicator.

What could be the biological reason why obesity promotes cancer?

We think that the most obvious evidence points towards sexual hormones and inflammatory chemical messengers that are produced by fatty tissue. It is an established fact by now that inflammation accelerates cancer. Sexual hormones act as growth factors promoting cancer growth in many cells. Additionally, obese people have elevated levels of the insulin-like growth factor (IGF), which also drives cellular growth.

Can people reduce their personal risk for cancer by losing weight?

That is what one would expect, but up until now there are no data to prove this! There are simply insufficient numbers of people who manage to reduce their weight substantially and then maintain their weight loss. However, there are small studies that indicate a trend in this direction: For example, extremely overweight women who were able to lose weight by surgically shrinking their stomach have a lower risk of contracting cancers of the breast and endometrium.

It is hard to lose weight permanently. Therefore, my personal advice is: Be careful not to gain pounds in the first place. Be careful also to prevent this in your children. This is a useful contribution to cancer prevention!

Read IARC press release:
http://www.iarc.fr/en/media-centre/iarcnews/2016/handbook16_iarc2016.php

Read article:
Lauby-Secretan B, Scoccianti C, Loomis D, Grosse Y, Bianchini F, Straif K; International Agency for Research on Cancer Handbook Working Group: Body Fatness and Cancer - Viewpoint of the IARC Working Group. New England Journal of Medicine 2016, DOI: 10.1056/NEJMsr1606602

* Source: The Lancet, April 2, 2016, DOI: http://dx.doi.org/10.1016/S0140-6736(16)30054-X

Today, there are considerably more people who are obese than people who are underweight.

In the wealthy, developed countries of the world, the rise in body mass index (BMI) has slowed down since 2000. Around that time, it had become common knowledge that overweight had turned into a serious problem for public health. In many other regions of the world, however, the BMI has continued to rise at an increasing pace since 2000. At the global level, this effect predominates.

Trends in the prevalence of obesity worldwide
Men: from 3.2 percent (1975) to 10.8 percent (2014)
Women: from 6.4 percent (1975) to 14.9 percent (2014)

**Body Mass Index, BMI: body weight in kilograms [kg] divided by the square of the height in meters [m].