In the past, strong evidence had linked five cancers to excess body weight:
- Breast cancer in postmenopausal women
- Colorectal cancer
- Uterine cancer
- Kidney cancer
- Esophageal cancer (adenocarcinoma type)
In April this year, the International Agency for Research on Cancer, funded by the American Cancer Society, convened a working group to reassess the preventative role of weight control in cancer. An expert panel reviewed, overall, some 1,000 studies. They established the term “body fatness” and used body mass index as their measure for it. The review found that the evidence was compelling enough to add eight additional cancers to the list of those linked to excess weight:
- Ovarian cancer
- Pancreatic cancer
- Stomach cancer (specifically, gastric cardia)
- Gallbladder cancer
- Liver cancer
- Thyroid cancer
- Multiple myeloma
- Meningioma (cancer of the tissue that surrounds the brain and spinal cord)
Together, these 13 cancers account for 42 percent of all new cancer cases, according to the chairman of the scientific panel, Graham Colditz of Washington University in St. Louis.
Why are there more cancers being connected to excess weight?
ACS noted that when the previous expert panel was convened for their 2002 report, there were smaller and far fewer studies, especially for some less commonly diagnosed cancers. Now there is a much larger body of evidence, primarily from much larger studies, including those where data are pulled from many individual studies. These studies allow better understanding of the associations of excess body weight with risk of less commonly diagnosed cancers.
There are many ways it contributes, and these are different for different types of cancer. For example, in postmenopausal women, fat cells are an important contributor to sex hormones, such as estrogen, that play a role in the development of endometrial and breast cancers, as well as some other cancers. But there are also other mechanisms that are thought to be important for different types of cancer. These include mechanisms related to abnormal glucose metabolism and excess insulin, altered immune responses, and obesity-related inflammation.
The expert panel also noted there is a body of preliminary evidence that intentional weight loss may also have a role in cancer prevention. The IARC working group reaffirmed that eating a diet too high in calories and not moving enough are important contributors to excess body fat, but they noted that the most important factor is an excess amount of calories.
Unfortunately, only about half of Americans know that body weight can increase the risk of developing cancer, according to a recent survey.