Study shows how high-fat diets increase colon cancer risk

Epidemiologists have long warned that, in addition to causing obesity, eating too much fat and sugar puts a person at greater risk for colon cancer. Now, researchers at Temple University have established a link that may explain why.

The findings, “Epigenetic Differences in Normal Colon Mucosa of Cancer Patients Suggest Altered Dietary Metabolic Pathways,” were published in the March issue of the American Association for Cancer Research’s journal, Cancer Prevention Research.

“There have always been questions about why things like diet and obesity are independent risk factors for colon cancer,” said Carmen Sapienza, professor of pathology in Temple’s Fels Institute for Cancer Research and Molecular Biology, the study’s lead author. “This study suggests how and why high fat diets are linked to colon cancer.”

The researchers compared colon tissue in non-colon cancer patients with normal colon tissue in patients with the disease. In the normal tissue from patients with colon cancer, they found that epigenetic marks on genes involved in breaking down carbohydrates, lipids and amino acids - abundant in the fatty Western diet - appeared to have been retrained. Epigenetic marks are chemical modifications that serve as on/off switches for many genes.

“These foods are changing the methylation patterns on a person’s insulin genes so that they express differently, pumping out more insulin than the body requires,” said Sapienza. “In people that have colon cancer, their glucose metabolic pathways and insulin signaling pathways are running at completely different levels than people who don’t have colon cancer.”

Sapienza said that cancer cells love insulin and studies have shown that tumors feed off of insulin. “Insulin is only supposed to be expressed in your pancreas, so having this extra insulin is bad,” he said.

Colorectal cancer is a disease in which cells in the colon or rectum become abnormal and divide without control, forming a mass called a tumor. (The colon and rectum are parts of the body’s digestive system, which takes up nutrients from food and water, and stores solid waste until it passes out of the body.)

Colorectal cancer cells may also invade and destroy the tissue around them. In addition, they may break away from the tumor and spread to form new tumors in other parts of the body.

Colorectal cancer is the third most common type of non-skin cancer in men (after prostate cancer and lung cancer) and in women (after breast cancer and lung cancer). It is the second leading cause of cancer death in the United States after lung cancer. Although the rate of new colorectal cancer cases and deaths is decreasing in this country, an estimated 141,210 new cases of colorectal cancer and 49,380 deaths from this disease are expected to occur in 2011.

Sapienza pointed out that people don’t usually get colon cancer until the age of 50 or older, so it is unclear when the epigenetic modification of the genes begins.