Diet Impacts Cancer, But The Magic May Not Be In Your Favorite Superfood

August 01, 2014

We’ve all heard the promises: Certain foods or diet strategies are supposed to have the power to prevent cancer. In some cases, ads for special drinks, supplements or potions are targeted to vulnerable cancer patients.

But as we all recognize, cancer is a pretty formidable opponent. Can what we ingest really have an impact on it?

Absolutely, says surgical oncologist Anton J. Bilchik, MD, PhD. Dr. Bilchik is the chief of medicine, interim chief of science and chief of the gastrointestinal research program at the John Wayne Cancer Institute.

“Emerging science, particularly over the last 10 to 20 years, points to an undeniable link between diet and cancer,” says Dr. Bilchik.

Diet is the cause of some 20% of all cancers, including endometrial, gallbladder, esophageal, renal, leukemia, thyroid, breast, pancreas, multiple myeloma, colon, non-Hodgkin lymphoma, liver and lung, according to a 2008 study in the journal Pharmaceutical Research. For cancers such as endometrial and colon, the link is thought to be even stronger.

Now prepare to be a little, well, underwhelmed. Fighting cancer isn’t about ingesting exotic—and expensive—nutrients or even eating organic magic foods celebrated for their cancer-preventing properties. It’s not about hard-to-follow diets that entirely eliminate, for example, carbohydrates or sugar. It’s not about shakes, teas or enemas.

Studies such as the ones published in the journal The Oncologist in 2010 and the 2008 Pharmaceutical Research paper conclude that being obese or overweight is the most convincing connection between diet and cancer.

“Weight is a very serious issue. It’s just behind cigarette smoking in terms of increasing our risk of so many cancers,” says Dr. Bilchik. “This doesn’t mean that average-weight people don’t get cancer, but it does mean that there is something we can do to decrease our risk.”

A recent study in the journal The Lancet demonstrates that obesity increases the risk of 22 different cancers, he says. It also suggests that different mechanisms are associated with different cancer sites.

Researchers believe that being overweight alters insulin, various other hormones, and the body’s inflammatory responses—all mechanisms that play a role in particular cancers. Furthermore, research suggests that cancer patients who are overweight tend to have worse outcomes than patients who are average weight.

Dr. Bilchik says, though, that he very often hears from patients who are convinced that certain nutritional strategies will help them. “If someone feels better— whether that’s physically or even psychologically—eating a certain way or taking a supplement in moderation, I don’t have a problem with that,” he says. “But I always warn against drastic measures, spending too much money or taking high doses of anything.”

He notes that many supplements or specialized diets haven’t been rigorously studied. He worries that some could even cause the exact opposite effect of what any patient wants.

“People make all kinds of claims. They’ll say that a certain diet works because it starves the cancer cells. But if you’re starving your cancer cells, you’re also starving the healthy cells that contribute to your body’s immune system to help fight the cancer. If you consider some of these claims carefully, they just don’t make much sense,” he says.

Furthermore, he warns that because a product is labeled “natural” or is widely available over the counter or online doesn’t mean it’s safe—particularly at high levels.

“We know that too much of certain supplements, for example, can damage the liver or kidneys. Other supplements can interfere with a patient’s medication,” he says. “So if you’re going to take something, it’s a good idea to clear it with your doctor first.”

There is data that points to the benefit of reducing red meat, fatty foods and alcohol, as well as eating plenty of fruits and vegetables, but Dr. Bilchik says the absolute best advice is even less complicated than focusing on particular foods.

“I recommend exercising and just eating a very balanced diet, including all the food groups, in moderation,” he explains. “That’s it. For right now, that’s what the scientific research concludes is effective because that’s what we know helps control body weight in a healthy way.”

Dr. Bilchik’s research receives generous support from the John Wayne Cancer Institute Auxiliary, the Doornink Family Foundation, Marguerite Perkins Mautner and the Sequoia Foundation.