Knowing that cancer risk is influenced by lifestyle empowers consumers to make healthful decisions like quitting smoking and protecting themselves from the sun. Likewise, the concept of an “anticancer diet” is deeply attractive to many people. Unfortunately, the connection between diet and cancer risk largely is shrouded in mystery.

Writing for Nutrition Today, Donato Romagnolo, PhD, and Ornella Selmin, PhD, of the University of Arizona Cancer Center and College of Agriculture and Life Sciences, delved into the current research to examine the Mediterranean diet’s association with the prevention of several chronic diseases, including colorectal cancer and breast cancer.

“The traditional Mediterranean diet is rich in fruits and vegetables, fish, olive oil and nuts,” said Dr. Romagnolo. “Compared with Western dietary patterns, it favors local and seasonal food production to a greater degree.”

Dr. Romagnolo contrasts the   Mediterranean diet with a standard “Western” diet, the pattern that dominates dinner tables across the United States.

“A Western diet tends to be higher in carbohydrates. There’s a lot more meat and protein,” Dr. Romagnolo explained. “Oils tend to be predominantly of vegetable origin, mostly soybean oil and corn oil — not olive oil.”

In the popular imagination, olive oil is a salient feature of the Mediterranean diet. Olive oil might reduce breast cancer risk, possibly by interfering with HER-2, a gene that can go “haywire” to fuel the growth of breast cancer cells.

Other compounds in olive oil, called phenols, might help reduce the proliferation of cancer cells while protecting genes that suppress tumors. Phenols also could be protective against chronic inflammation, which can cause tissue damage and raise risk for cancer.

Fiber, Red Meat and Colorectal Cancer

Fiber intake is associated with risk for colorectal cancer — high-fiber diets are protective, while low-fiber diets increase risk. One review calculated that colorectal cancer incidence might be reduced by up to 11 percent if people in Western countries shifted to a Mediterranean diet.

“There are two aspects to the fiber story,” explained Dr. Romagnolo. First, “fiber encourages the speed at which food moves through the intestine. The mechanical effect of the fiber helps to eliminate other carcinogens.”

Second, fiber from fruits, vegetables and whole grains helps cultivate a healthy microbiome — the community of microbes that live in your gut. High-fiber foods support “good” bacteria, such as Bifidobacteria and Labtobacilli, which help reduce inflammation.

“Fiber favors the growth of bacteria that produce byproducts that are completely different from those that grow on starches,” Dr. Romagnolo said. “The byproducts of fermentation of fiber are two fatty acids: acetate and butyrate. Butyrate has been suggested as a cancer preventative.”

On the flipside, meat contains no fiber, and when it overshadows the rest of a diet it can push fiber-rich foods off the plate. Beyond the fiber issue, Dr. Romagnolo particularly is interested in the way red meat is processed and cooked, which may have negative health effects. When it is cooked, the iron in red meat interacts with nitrogen additives to modify them into forms that can damage DNA, hastening cancerous mutations.

“The cooking is producing these carcinogens,” said Dr. Romagnolo. “You have a combination of nitrates that are added to the meats to preserve them, and the iron coming from the hemoglobin component [of red meat]. The two of them make a perfect storm.”

The Mediterranean Diet and Breast Cancer

The same review pointing to the Mediterranean diet’s role in reducing colorectal cancer risk also shows that about 25 percent of breast cancer diagnoses could be prevented by switching from a standard Western diet to a Mediterranean diet.

“Studies show that individuals who adopt the Mediterranean diet, women in particular, had reduced circulating estrogen,” said Dr. Romagnolo. Estrogen is a hormone that stimulates the growth of breast cells, and exposure to estrogen is a risk factor for breast cancer.

Another idea is that carotenoids in the Mediterranean diet reduce risk for chronic inflammation, thereby reducing cancer risk. Carotenoids are the pigments that give foods like carrots, red bell peppers and kale their bright colors.

The bad news is that alcohol is a known risk factor for breast cancer — and that includes red wine, which many people associate with the Mediterranean diet.

“Estimates suggest a 30 to 50 percent increase in breast cancer risk from 15 to 30 grams per day of [pure] alcohol,” said Dr. Romagnolo. “Wine consumption should be controlled — no more than one glass a day. People may think, ‘Oh, wine is good for you.’ Well, not for breast cancer.”

Diet and Cancer: Exploring the Connection

Although the link between diet and cancer risk is unclear, the current body of evidence suggests that certain dietary patterns, like the Mediterranean diet, can be protective.

“To get on the ball, we need randomized controlled trials,” said Dr. Romagnolo. “We can test the effect of diet in a controlled environment. You need to have a large number of subjects. Until we do those, I’m afraid we won’t know the answer for sure.”

But finding these answers will be an important step forward in disease prevention.

“It will be another tool to reduce cancer incidence,” Dr. Romagnolo explained. “If you don’t smoke, if you don’t drink heavily, if you aren’t exposed to some environmental chemicals, diet is the most significant exposure.”

And, just as people have a large degree of control over exposures like smoking and drinking, so too can they exercise some control over their diets. Learning more about the connection between diet and cancer risk provides the information necessary to make informed decisions about what we put on our plates.