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.



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Comments (10) Read through and enter the discussion with the form at the end
Steve - April 9, 2012 2:12 PM

Interestingly it says, "The authors HYPOTHESIZE that an unhealthy diet full of refined carbohydrate and excess fat may cause this metabolic change"

So now we need the real science to prove that the hypothesis is correct. I rather suspect that the refined carbohydrates are causing the real problem along with the refined or highly processed fats sharing the blame, especially the hydrogenated fats. But let's not blame all fats without conclusive evidence. Although, since you used the word "excessive, then yes, excessive in itself would mean excessive to an unhealthy degree, but what is the definition of "excessive"? What is an unhealthy degree? After all some fats may be innocent bystanders. Remember, decades ago before everyone consumed so much refined sugar and High Fructose Corn Syrup, we didn't have nearly the problems that we do today with cancer, yet folks in those days didn't concern themselves with restricting dietary fats, whereas today all the emphasis is on low-fat or reduced fat. If you remove the fat from foods that naturally contain fat then they are no longer whole foods but if you are going to pasteurize dairy and then homogenize it to boot, it ain't natural anyway, so you may as well do whatever you want to it cause I won't touch it anyway.

Dr. Eric Mitz - April 9, 2012 3:59 PM

I love articles that explain complex ideas in simple terms. So many of our patients have heard the mantra that refined carbs and "bad" fats are harmful, but few of them could be expected to understand why. Shared!

Diane Lassen - April 9, 2012 5:36 PM

I think the most important thing to prevent colon cancer is to keep the wastes moving out of the body instead of hanging out in the colon with the toxins being reabsorbed. I find that my patients and clients think that having a bowel movement once every other day is normal. it is not!! I advocate a plant-based diet, and a green smoothie every day to ensure 2 bowel movements a day!!! I do like small quantities of raw milk, and raw milk cultured cheeses, and I find that they make a good addition to salads and are a good protein source.

mike rubino - April 9, 2012 9:01 PM

Kind of scary that yesterday I just watched my family poison themsleves with white flour , cheeses , potatoes, cookies, pies, pastries , candies, etc. from 93 to a year and a few months they were all eating this stuff like ther eis no tomorrow . I should print this article and save it for the next time around.

RICK - April 10, 2012 10:26 AM

Let's say we are eating a healthy whole foods plant based diet. Is adding a few baked white potatoes topped with salsa really a problem?

Does anyone know the nutritional value of purple potatoes? I love these things. I love cutting them open and seeing the blue/purple color. I am under the assumption that blue/purple color means they are loaded with phytonutrients. Does anyone know if that is true?

Linda - April 11, 2012 8:55 AM

I would like clarification of the following statement:
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.

I thought insulin was only made/secreted from the pancreas, not from colonic cells. Do colon cells actually make insulin, or did you mean that they spur increased insulin release by the pancreas?

Deana Ferreri, Ph.D. - April 11, 2012 3:56 PM

Insulin is only produced and secreted by the pancreas in significant quantities, but all cells have the gene for insulin and other cell types may produce small amounts. In this study, they compared mRNA levels of insulin to confirm that the DNA methylation was actually changing gene transcription. mRNA levels were higher in the colon cancer patients, indicating greater production. The colon cells would not have to secrete insulin for a pro-growth effect - a significant level of intracellular insulin is found in many tumor types and is thought to promote cancerous growth.

Joel Fuhrman, M.D. - April 11, 2012 4:01 PM

Rick, no a few baked potatoes a week are not a problem, I do not even think one a day would be a problem if the diet was overall favorable. The problem is when white potato, white rice, or white flour and maybe other high glycemic foods are all combined daily to make the overall diet glycemically unfavorable or if too many of those high glycemic foods (including white potato) are used in the diet, which also exclude the higher nutrient, lower glycemic vegetables, beans, seeds, nuts, squashes and fruits and then the diet could no longer be considered optimal, and especially metabolically unfavorable with an overweight, diabetic prone individual.

Linda - April 12, 2012 7:54 AM

I would be very interested in perusing a list of glycemic load for many foods common to a Nutritarian diet; could you direct me to a trustworthy site which would have this information available? Thank you. And thank you for the clarification, Dr. Ferreri; looks like what you are saying is that actual body-wide insulin change because of those specific cells is not substantial, but is significant as a flag to what is occurring throughout the body.

Deana Ferreri, Ph.D. - April 12, 2012 8:26 AM

The most comprehensive list of GI and GL values I am aware of can be found in this paper published in Diabetes Care (

The tables are in the online supplement to the paper:

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