Excess energy from food is stored as fat in the body inadipose tissue. The amount of this body tissue varies more from person to person than any other type (such as muscle, bone or blood). The size and location of these fat stores also vary considerably between populations, people, and over the course of a person’s life.
Fat is not distributed equally around the body. It accumulates subcutaneously (beneath the skin) around the muscles of the upper arm, buttocks, belly, hips, and thighs. It also accumulates intra-abdominally or viscerally (around the organs). Increases in body weight during adulthood depend mostly on accumulation of fat rather than lean tissue, and therefore any change may better reflect fatness than adult attained weight itself, which is more dependent on lean mass.
The evidence that greater body fatness is a cause ofadenocarcinomaof the oesophagus, and cancers of the pancreas, colon, breast, endometrium, and kidney is convincing. Some of the mechanisms by which body fatness increases the risk of cancer are well understood.
Obesityinfluences the levels of a number of hormones and growth factors.Insulin-like growth factor1 (IGF-1), insulin, andleptinare all elevated in obese people, and can promote the growth of cancer cells. In addition, insulin resistance is increased, in particular by abdominal fatness, and the pancreas compensates by increasing insulin production. This hyperinsulinaemia increases the risk of cancers of the colon andendometrium, and possibly of the pancreas and kidney. Increased circulating leptin levels in obese individuals are associated with colorectal and prostate cancers.
Sex steroid hormones, including oestrogens, androgens, and progesterone are likely to play a role in obesity and cancer. Adipose tissue is the main site of oestrogen synthesis in men and postmenopausal women. The increased insulin and IGF-1 levels that accompany body fatness result in increased oestradiol in men and women, and may also result in higher testosterone levels in women. Increased levels of sex steroids are strongly associated with risk of endometrial and postmenopausal breast cancers, and may impact on colon and other cancers.
Obesity is characterized by a low-grade chronic inflammatory state, with up to 40 per cent of fat tissue comprising macrophages. The adipocyte (fat cell) produces pro-inflammatory factors, and obese individuals have elevated concentrations of circulating tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and C-reactive protein, compared with lean people, as well as of leptin, which also functions as an inflammatory cytokine. Such chronic inflammation can promote cancer development.
-aadautech, a cancer drug discovery and therapeutics blog