Together, the American Institute for Cancer Research and the World Cancer Research Fund have reviewed the data available on the diet, weight, and lifestyle of 29 million people in a bid to discover the most effective ways to prevent colorectal cancer.
The report is part of the Continuous Update Project, which is an initiative that gathers data on cancer prevention through nutrition and lifestyle and whose findings inform official guidelines and policies for cancer prevention.
"Colorectal cancer is one of the most common cancers, yet this report demonstrates there is a lot people can do to dramatically lower their risk," says lead report author Dr. Edward L. Giovannucci, a professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health in Boston, MA.
Colorectal cancer ranks as the fourth most common type of cancer across the globe, as well as the fourth deadliest form of cancer.
In 2012, approximately 1.4 million new cases were diagnosed. Furthermore, 700,000 cancer deaths are thought to have been caused by colorectal cancer.
However, the report shows that there is a lot that can be done to prevent this killer. "The findings from this comprehensive report are robust and clear: diet and lifestyle have a major role in colorectal cancer," says Dr. Giovannucci.
Whole grains and physical activity lower risk
The report looked at 99 studies from all over the world, summing up data on 29 million adults of whom 247,000 developed colorectal cancer.
The studies that the researchers examined included only randomized controlled trials, cohort studies, and so-called nested case-control studies.
After conducting meta-analyses of these studies, the researchers found that eating whole grains every day significantly reduces the risk of colorectal cancer, while the intake of processed meats raises the risk.
More specifically, eating more than 500 grams of cooked red meat (such as pork, beef, or lamb) every week raises the odds of developing colorectal cancer, with every 100 grams per day further increasing the risk by 12 percent.
The report also found that consuming more than two alcoholic drinks every day - or the equivalent of 30 grams of alcohol - as well as being overweight or obese further increases the risk.
By contrast, around three daily servings, or 90 grams, of whole grains (including brown rice and whole-wheat bread) can lower the risk of colorectal cancer by 17 percent.
Fruits and vegetables containing vitamin C, as well as fish, also seemed to lower the risk of colorectal cancer, although the evidence was not as clear and more data are needed.
Oranges, grapefruits, strawberries, kiwis, broccoli, spinach, and sweet red pepper are all good sources of vitamin C.
At least 30 minutes of physical activity every day was also found to lower the risk. The review found that the highest levels of physical activity decreased the risk by 20 percent.
Colorectal cancer could be prevented
"Many of the ways to help prevent colorectal cancer are important for overall health," says Dr. Giovannucci.
"Factors such as maintaining a lean body weight, proper exercise, limiting red and processed meat, and eating more whole grains and fiber would lower risk substantially. Moreover, limiting alcohol to at most two drinks per day and avoidance or cessation of smoking also lower risk."
Dr. Edward L. Giovannucci
Alice Bender, Director of Nutrition Programs at the American Institute for Cancer Research (AICR), also weighs in on the findings. She says, "Replacing some of your refined grains with whole grains and eating mostly plant foods, such as fruits, vegetables, and beans, will give you a diet packed with cancer-protective compounds and help you manage your weight, which is so important to lower risk."
"When it comes to cancer there are no guarantees, but it's clear now there are choices you can make and steps you can take to lower your risk of colorectal and other cancers," says Bender.
In fact, the AICR suggest that 47 percent of colorectal cancer cases in the United States could be prevented by changing our lifestyle.