Refined carbohydrates and excess fats may drive the insulin gene in colon cells to promote cancer

Colon cancer is the third most common cancer type, and the second leading cause of cancer death in the U.S.1 These cancers are the ones most closely linked to lifestyle; the good news is, that means that colon and rectal cancers are also highly preventable by following healthful lifestyle habits – including avoiding disease-causing foods.

Scientists believe that elevated insulin levels contribute to cancer development; insulin in high concentrations may promote growth and division of cancer cells, and cancerous cells often have elevated levels of insulin receptors.2 Foods with a high glycemic load (GL) such as white bread, white rice, sugar, and white potatoes, produce dangerous spikes in blood glucose, and consequently insulin levels. Diets including large quantities of high GL foods increase the risk of several chronic diseases, and a meta-analysis of several studies found a 26% increase in colorectal cancer risk in people who consumed the most high glycemic load foods in their diets.3,4

Examples of high, medium and low GL carbohydrate sources:5,6

High GL (20 or higher)  
White potato (1 medium baked) 29
White rice (1 cup cooked) 26
Medium GL (11-19)  

Black rice (1 cup cooked)

Low GL (1-10)  
Butternut squash (1 cup cooked) 8
Kidney beans (1 cup cooked) 7

According to the American Institute for Cancer Research, there is suggestive evidence that cheese and foods containing animal fats increase the risk of colon and rectal cancers. Cheese, the fattiest food in the American diet, is particularly high in saturated fat, which is known to impair insulin sensitivity.7,8

Research suggests that over time, these dietary factors – excess, low-nutrient carbohydrate and fat – may disturb carbohydrate and fat metabolism in the colon by altering DNA methylation in colon cells.

DNA methylation acts essentially as an on/off switch for a gene, usually decreasing (but sometimes increasing) the amount of protein made from that genetic code. Dietary factors are known to affect DNA methylation, and too much or too little methylation can contribute to the development of cancer.9

A study compared methylation patterns of thousands of genes in the colon mucosa of control subjects without colon cancer to normal mucosa of colon cancer patients; the researchers found hundreds of genes whose methylation patterns differed in the two sets of subjects. When they looked at those genes with the greatest differences in methylation, they made an interesting observation: a common theme among many of these genes was that they are involved in carbohydrate and lipid metabolism – one of these was the insulin gene. In short, “normal” colon cells in colon cancer patients were making more insulin than normal colon cells from healthy subjects – and we know that excess insulin promotes cancer.

The authors hypothesize that an unhealthy diet full of refined carbohydrate and excess fat may cause this metabolic change – and once excess insulin is being produced by colon cells, it then feeds the growth of cancerous cells.10

Though the research may be complex, the message is simple: refined foods like sugar and white bread, and low-nutrient fats like oils and cheeses are harmful to the health of your colon. Colon cancer is a preventable disease – whole, natural foods provide the fiber, resistant starch, and phytochemicals that will keep the cells of the colon healthy and expressing the proper genes in the proper amounts.



1. American Cancer Society. What are the key statistics about colorectal cancer? [ ]
2. Vigneri P, Frasca F, Sciacca L, et al: Diabetes and cancer. Endocr Relat Cancer 2009;16:1103-1123.
3. Gnagnarella P, Gandini S, La Vecchia C, et al: Glycemic index, glycemic load, and cancer risk: a meta-analysis. Am J Clin Nutr 2008;87:1793-1801.
4. Barclay AW, Petocz P, McMillan-Price J, et al: Glycemic index, glycemic load, and chronic disease risk--a meta-analysis of observational studies. Am J Clin Nutr 2008;87:627-637.
5. Carbohydrates and the Glycemic Load. Harvard School of Public Health: The Nutrition Source. 
6. Atkinson FS, Foster-Powell K, Brand-Miller JC: International tables of glycemic index and glycemic load values: 2008. Diabetes Care 2008;31:2281-2283.
7. WCRF/AICR Expert Report, Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective.: World Cancer Research Fund; 2007.
8. Vessby B, Uusitupa M, Hermansen K, et al: Substituting dietary saturated for monounsaturated fat impairs insulin sensitivity in healthy men and women: The KANWU Study. Diab tologia 2001;44:312-319.
9. Kulis M, Esteller M: DNA methylation and cancer. Adv Genet 2010;70:27-56.
10. Study shows how high-fat diets increase colon cancer risk. 2012. EurekAlert! Accessed March 28, 2012.