Writing in the New England Journal of Medicine, oncology experts found sufficient evidence linking overweight individuals with a higher risk of cancer of the gastric cardia (stomach), liver, gallbladder, pancreas, ovary, thyroid, meningioma (brain) and multiple myeloma (blood).
The experts, assembled by the International Agency for Research on Cancer (IARC), also presented more limited evidence that excess body fat increases the risk of male prostate and breast cancer as well as diffuse of large B-cell lymphoma (cancer of the white blood cell).
Figures outlining the scale of obesity worldwide make for grim reading. In 2014, more than 640 million adults (an increase by a factor of six since 1975) and 110 million children and adolescents in 2013 (an increase by a factor of two since 1980) were considered obese.
The working group of 21 independent researchers evaluated more than 1,000 studies, including intervention trials, cohort and case–control studies, animal studies and studies on the mechanisms linking excess body fat and cancer.
As a result, the findings were based on increased risks linked with excess weight rather than interventions that could reduce the risks.
The majority of the studies provided risk estimates for adult body mass index (BMI). Some studies provided estimates for BMI or body shape in childhood or adolescence, BMI changes over time or other indicators of fat content such as waist circumference.
Fat chance of improvement?
“This evaluation shows that the number of cancers due to overweight and obesity is higher than previously estimated,” said Dr Beatrice Lauby-Secretan, lead study author and a scientist in charge of IARC’s Handbooks of Cancer Prevention Series.
“With the increasing prevalence of obesity worldwide, the overall burden of disease linked to the obesity epidemic will still increase in the coming years.”
The findings follow earlier conclusions outlined in the IARC Handbooks (Volume 6, published in 2002) that excess weight carried by an individual could increase the risk of cancers of the colon and rectum, oesophagus, kidney, breast in postmenopausal women and of the uterus.
“Studies in experimental animals clearly show the beneficial effect of losing weight in reducing the risk of cancer. However, there are only few intervention studies (in humans) on the beneficial effect of losing weight in reducing cancer risks,” said Lauby-Secretan.
“More such studies are necessary in order to be able to establish a firm link. Of interest, a few studies in cancer patients have suggested that weight loss for overweight or obese cancer patients may increase their survival and reduce cancer recurrence,” she added.
Obesity can be avoided
Obesity is caused by excess energy intake and physical inactivity - two modifiable risk factors that contribute to the unprecedented obesity rates seen across the globe.
“Obesity has become an epidemic and should be tackled at all possible levels,” said Lauby-Secretan. “It has been shown that overweight and obesity in childhood and adolescent also increase the risk of cancer in adults.”
“Keeping a healthy body weight from the earliest age is the most efficient way to avoid being overweight or obese later in life.”
Source: New England Journal of Medicine
Published online ahead of print, DOI: 10.1056/NEJMsr1606602
“Body Fatness and Cancer — Viewpoint of the IARC Working Group.”
Authors: Béatrice Lauby-Secretan et al.