Cancer Risk and Cancer Survivors

Stopping Colon Cancer Before It Starts

Colon cancer is among our most preventable cancers. Prevention, however, is not likely to come from a single lifestyle choice, but from the combined influence of several choices – from a pattern of healthy living. The question now lies in identifying the key elements of that pattern.

A colon adenoma, or polyp, is a benign growth. Not all polyps turn into cancer, but almost all colon cancers start as polyps. The more polyps we prevent, the more potential colon cancers we stop.

Stopping cancer before it starts is one of the key measures of success in the ongoing Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO). A recent paper published in 2007 in the Journal of Nutrition sought to classify trial participants according to which of three sets of healthy eating guidelines they most closely followed.

In the study, participants in the PLCO trial, which includes more than 37,000 adults aged 55 to 74, were linked to one of three plant-based diets that emphasized vegetables and fruits and limited alcohol consumption. The diet patterns varied in their emphasis on restricting saturated fat and sugar and selecting whole grains over refined grains. Some of the diets focused on getting enough meat and dairy products while others concentrated on avoiding excess.

The results of the analysis showed a clear relationship between diet and colon cancer risk. Among men, those who most closely followed any of the three defined eating patterns were 20 to 25 percent less likely to develop a polyp than those whose diets least resembled the guidelines. Women’s risk of developing polyps was also reduced (by an average of 18 percent), but only among those who most closely followed one particular eating plan, the USDA Food Guide recommendations.

Dietary intervention trials have shown similar success in the past, but the question remains whether these interventions yield long-term benefits. The Polyp Prevention Trial (PPT), which focused on the role of a high-fiber, plant-rich, low fat diet in preventing polyps, was recently revisited. A 2007 eight-year follow-up report showed no difference in polyp development between those participants who were assigned to the intervention diet and those given no dietary instructions.

Researchers suspect that perhaps some of the benefits of following a healthy eating pattern are overwhelmed by the additional risks that overweight subjects incurred. In the PPT study, for example, the diet group began the study mostly overweight and lost less than two pounds.

Studies are increasingly inconsistent in showing the protective effects of a diet focused on vegetable and fruit consumption. One clear message is emerging from the research, however: Eating a Western-style diet (emphasizing meat and refined carbohydrates) can be toxic. Several studies have shown that people who most closely follow a Western diet are 30 to almost 200 percent more likely to develop polyps compared to those whose diet least resembles this pattern. One of these studies also showed a 42 percent increased risk of polyps with high alcohol consumption.

As we get more data from studies like these, our task is to sift through the research and identify the steps that seem most important in lowering risk. A major international report on diet and cancer prevention published by the American Institute for Cancer Research in 2007 identified the most important steps as follows: weight control, regular physical activity, limited consumption of red and processed meat and limited alcohol consumption. Adequate fiber from whole grains, vegetables, fruits and beans and adequate calcium from milk or other sources were also identified as probably protective.