Cancer and diet: What’s the connection?
Your dietary habits can promote cancer or protect against it.
The link between cancer and diet is just as mysterious as the disease itself. Much research has pointed toward certain foods and nutrients that may help prevent—or, conversely, contribute to—certain types of cancer.
While there are many factors you can't change that increase your cancer risk, such as genetics and environment, there are others you can control. In fact, estimates suggest that less than 30% of a person's lifetime risk of getting cancer results from uncontrollable factors. The rest you have the power to change, including your diet.
Keep in mind that most research only points to associations between diet and cancer, and not necessarily a cause-and-effect relationship. "It not 100% certain that consuming more or less of certain foods or nutrients will guarantee cancer protection," says Dr. Edward Giovannucci of Harvard's T.H. Chan School of Public Health. "But science has found that certain dietary habits tend to have a greater influence." Here is a look at four areas that stand out.
Processed and red meat
Processed meat is any meat that has been smoked or fermented or includes added salt and nitrites to enhance flavor. The connection between processed meat and cancer is consistent, says Dr. Giovannucci. For instance, about 30 prospective studies of colorectal cancer—the third most diagnosed cancer in men—found that eating around 50 grams a day of processed meat (about 2 ounces) is associated with about a 20% increase in colorectal cancer risk. The risk factors are similar for red meat, too. "The exact mechanism is unclear, but it may be related to the added nitrates in processed meat and the heme iron inherently found in red meat," says Dr. Giovannucci.
Antioxidants
Antioxidants no doubt are important for cancer prevention, as they help neutralize free radicals that can damage cells. But the larger question is whether taking more through your diet or supplements further reduces your risk.
So far the research to support the more-is-better approach has not been impressive, says Dr. Walter Willett of the T.H. Chan School of Public Health. "We don't yet know how long you would need to take extra antioxidants for a benefit to be seen," he says. "Some cancers develop over many decades, and you may need to increase dietary antioxidants in your early years to see a benefit."
Still, it's important to consume foods high in antioxidants, since they offer other benefits, too, like improved cardiovascular health. Dr. Willett's suggestion: do not target individual antioxidants, but instead aim for a diet that includes a variety of high-antioxidant foods. "Focus on bright colors, such as dark green, orange, purple, and red fruits and vegetables—for instance, spinach, carrots, and tomatoes."
Glycemic index
Carbohydrates have a Jekyll-and-Hyde role with cancer: they can be good or bad depending on the source. Glycemic index (GI), a measure of how fast carbohydrates turn into sugar in the blood, helps us tell the good from the bad.
A study of 3,100 people, presented at the 2016 Experimental Biology forum, found that consuming foods with a high GI (70 or higher on the 100-point GI scale) was associated with an 88% greater risk for prostate cancer. High-GI items include sugar-sweetened soft drinks, fruit juices, and processed foods like pizza.
On the flip side, eating lower-GI foods like legumes (beans, lentils, and peas) was linked with a 32% lower risk of both prostate and colorectal cancers. Another study, published March 2015 in Cancer Epidemiology, Biomarkers & Prevention, linked a high-GI diet with lung cancer, the second most common cancer among men. The study showed an almost 50% increase in risk among people with the highest GI diet compared with those with the lowest.
Low- and medium-GI foods rank from zero to 69 on the GI scale. For a list of common foods and their GI values, visit www.health.harvard.edu/glycemic.
Calcium
Some evidence suggests higher calcium intake can lower the risk for cancer, especially colorectal cancer. Researchers believe calcium binds to bile acids and fatty acids in the gastrointestinal tract. This acts as a shield to protect cells from the damaging stomach acids.
However, other research has shown that extra calcium—2,000 milligrams (mg) or more per day—may be linked to a higher risk of prostate cancer.
"We do not know for certain why calcium has such a wide influence on cancer," says Dr. Giovannucci. "Your best bet is to keep your daily calcium intake to 500 mg to 1,000 mg per day, either from food like dairy products or supplements."
Weight gain and cancer
Another way to look at diet's role in cancer prevention is in terms of weight management. Modifying your diet can keep your weight under control, which offers even more protection.
A 2014 study in The Lancet found that a higher body mass index increases the risk of developing some of the most common cancers. Scientists discovered that among five million people studied, gain of 34 pounds was linked with a 10% or higher risk for colon, gallbladder, kidney, and liver cancers. The connection? Experts say body fat produces hormones and inflammatory proteins that can promote tumor cell growth.
Cancer prevention is often a matter of lifestyle
While diet and weight loss are central for cancer prevention, combining a good diet with other healthy habits can further lower your risk, according to a study in the May 2016 issue of JAMA Oncology.
Harvard researchers examined four main lifestyle areas that are associated with health status: smoking, drinking, weight, and exercise. They looked at 46,000 men over 26 years and classified about 12,000 as a low-risk group because they engaged in defined healthy behavior in all four areas—they did not smoke, drank moderate amounts of alcohol (no more than two servings per day), had a body mass index of 18.5 to 27.5, and engaged in 150 minutes of moderate-intensity exercise per week.
When they compared these men with others who did not meet these standards, the researchers discovered that men could avert or delay 67% of cancer deaths and prevent 63% of new malignancies each year. In terms of specific cancers, men could reduce incidence of bladder cancer by 62%, prostate cancer by 40%, and kidney cancer by 36%.
Article Published by Harvard Health Publishing
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