The lifetime risk of developing colorectal cancer, which is higher in developed countries, appears to be 4.6% for men and 3.2% for women (Chu et al. 1994).
Obesity, particularly abdominal obesity, is associated with an increased risk (Martinez et al. 1999; Russo et al. 1998) whereas physical activity is associated with a decreased risk of colorectal cancer (Giovanucci et al. 1996). There is also an association between diabetes mellitus and colorectal cancer risk; the risk is increased with a high fasting glucose level, high insulin levels, and obesity (Ma et al. 1999; Schoen et al. 1999).
Insulin plays an active role in promoting tumor growth via angiogenesis. Insulin is a growth factor that stimulates glycolysis and the proliferation of many cancer cell lines. Insulin is thought to facilitate angiogenesis by increasing lactic acid production in hypoxic tumor cells and by stimulating the proliferation of vascular cells. In cancer patients, elevated levels of insulin are common in cancerous tissue and blood plasma. It is therefore suggested that both a low sugar and a low saturated fat diet be followed.
Natural compounds have been reported to inhibit cancer-promoting effects of insulin. For example, vitamin C has been reported to increase oxygen consumption and reduce lactic acid production in tumor cells. In addition, some natural compounds may help reduce insulin production by reducing insulin resistance. Insulin resistance occurs when cells are no longer sensitive to insulin and thus more insulin is produced in an effort to reduce glucose levels.
Insulin resistance has been implicated as a risk factor for cancer, and diets high in saturated fats and omega-6 fatty acids promote insulin resistance. Although the exact pathway is unknown, it is thought that the mechanism of action is via chronic activation of protein kinase C (PKC). Some of the known natural compounds that can reduce insulin resistance include omega-3 fatty acids, curcumin, flavonoids, selenium, and vitamin E.