The International Agency for Research on Cancer (IARC) today released a summary of its report on the likelihood that excess body fat is linked to cancer. IARC is the cancer agency of the World Health Organization.
The summary is published in The New England Journal of Medicine. Led by Dr. Béatrice Lauby-Secretan, the IARC Handbook Working Group evaluated the current research findings linking excess fatness (overweight status and obesity) to various types of cancer.
They primarily included epidemiological data on 1000 human studies and also some animal studies. Most of the human studies were observational and investigated cancer risk as it relates to excess body fat — a few dealt with weight loss or weight control interventions.
Most of the studies provided risk estimates based on adult Body Mass Index (BMI). They sought to find the increase in relative risk of cancer, associated with excess body weight, relative to normal BMIs (18.5 to 24.9). Using data from meta-analyses or pooled analyses, the researchers concluded the following: For cancers of the colon, stomach, liver, gallbladder, pancreas and kidney; they found increased relative risks of 1.2 to 1.5 for those overweight (BMI 25-29.9) and 1.5 to 1.8 for those with obesity (BMI over 30).
For those with extreme obesity (BMI of 40 or more), the relative risk for esophageal adenoarcinoma was 4.8. The evidence for the various types of cancers was not always strong, but there were some for which the working group found sufficient evidence (listed below with their relative risks).
- Esophagus: 4.8
- Gastric cardia: 1.8
- Colon and Rectum: 1.3
- Liver: 1.8
- Gallbladder: 1.3
- Pancreas: 1.5
- Postmenopausal breast: 1.3
- Uterus (not cervical): 7.1
- Ovary: 1.1
- Kidney: renal cell: 1.8
- Meningioma: 1.5
- Thyroid: 1.1
- Multiple Myeloma: 1.5
The authors commented, "On the basis of the available data, we concluded that the absence of excess body fatness lowers the risk of most cancers."
Although many of these increases in relative risk are small, the fact that — according to the report — over 600 million adults are obese worldwide means that even a small increase in risk could have a substantial impact on cancer rate. These data are, of course, derived from secondary analyses of studies.
And, as we have noted on previous reports, BMI has its problems as an index of body fatness (see essay here).
Despite these caveats, such data reviews should lead both healthcare providers and the public to pay more attention to the issue of excess body fat.