Abstract

Prospective epidemiological observations consistently show a positive association between increasing Body Mass Index (BMI) and several cancers.  This is interpreted by the World Cancer Research Fund (WCRF) Continuous Update Project (CUP)independent expert panel as reflecting an effect of inceasing adiposity. Though curvilinear the relation is seen throughout the range of BMI reflecting a healthy weight, and beyond to overweight and obesity.  The WCRF CUP has concluded that there is strong evidence that increasing adiposity is a contributory cause to 10 different cancers (postmenopausal breast, colorectum, advanced prostate, kidney, endometrium, gallbladder, oesophageal adenocarcinoma, pancreas, liver and ovary).  Increasing physical activity reduces the likelihood of excess adiposity, and so contributes indirectly to reducing risk of these cancers. There is mounting evidence that physical activity also has a direct protective effect in additon to its impact on adiposity against cancers of the breast (postmenopause), endometrium and colon.  There is evidence that obesity promotes insulin resistance and increases exposure to growth factors, as well as generating a low grade systemic inflammatory response, both of which have tumour promoting potential. In addition postmenopausal obesity promotes oestrogen production through the action of aromatase, which fosters tumour growth in hormone-sensitive tissues.  Increasing physical activity also reduces inflammation and modulates metabolism of growth factors and their binding proteins to reduce cancer risk.  In patients already diagnosed with breast cancer, obesity and low levels of physical activity are markers of adverse outcome, though it  remains unclear whether or not these are causal factors in this context . Within England NIHR has established a Cancer and Nutrition infrastructure collaboration to help promote a coherent approach to translational research in nutritonal aspects of cancer, from prevention through to management and palliation.