Body Fatness and Cancer

17 August 2016

Guest Blog: Professor Annie S. Anderson

For decades cancer has been associated with weight loss and under nutrition. Cancer survivors still report health care staff being concerned if they report a decreased body weight – even if this is due to intentional weight loss.

Today's paper from the International Agency for Research on Cancer (IARC) provides a timely reminder about why we need to take the growing evidence on excess body fat and the opportunity for cancer risk reduction seriously.

Avoiding Weight Gain
The last cancer prevention handbook from IARC was published in 2002 when it was reported that avoidance of weight gain was associated with cancer–preventive effects in 5 cancers (colon, oesophagus, kidney, breast (postmenopausal) and uterus). As the years roll by, the world gets heavier and cancer occurence increases.

In this latest paper (a summary for the forthcoming handbook) IARC now reports a further 8 cancers (stomach (cardia), liver, gall bladder, pancreas, ovary, thyroid, multiple myeloma and meningioma) that could be reduced by the absence of excess body fat. New analysis including Mendelian randomisation approaches in colon and oesophageal cancers show consistent results with those obtained from cohort and case-control studies.

For female cancers, the findings provide lots of reasons why women should be supported for weight management. For cancer risk reduction of post–menopausal breast cancer avoiding excess weight and avoiding body-weight gain in adulthood are key features. Ovarian cancer has a similar profile. The potential reduction for endometrial cancer was estimated to be exceedingly high (RR 7.14 (6.33-8.06) highest versus normal BMI) especially in women who had never used HRT.

Whilst excess body fat in adults increases risk, the paper also reported an association between BMI in childhood, adolescence and early adulthood. This is surely a reminder of the importance of lifetime exposures and about the opportunity to reduce cancer incidence by strong and robust child and adult obesity policies. A focus on childhood is important but will never be enough.

Sceptics (like the women we interviewed in routine breast screening clinics in Scotland) of the links between obesity and cancer might be interested to know that there are now several plausible mechanisms for how excess body fat impacts on cancer risk. These include sex hormone metabolism and chronic inflammation pathways as well as a role for insulin and insulin like growth factor and even more encouraging is the evidence that intentional weight loss affects these bioactive pathways.

Cancer incidence predictions in Scotland do not bode well – but these aren’t all related to an ageing population. There are opportunities to reduce our cancer rates well beyond tobacco control and a strong obesity policy is one of them.

Professor Annie S. Anderson 
Member, IARC working group on Body Fatness and Obesity
Co-Director, Scottish Cancer Prevention Network 
Professor of Public Health Nutrition, University of Dundee