How plant-based food helps fight cancer

Eating more fruits and veggies may help prevent a third of cancer cases. Here's what we know.

By Mayo Clinic Staff

Cancer is the second-leading cause of death in the U.S. But estimates suggest that as many as a third of cases could be prevented with diet and nutrition alone.

The recipe? Many experts recommend filling your plate with foods that grow from the ground. Decades of research suggests that the best diet for cancer prevention is all about plants. That means lots of fruits, vegetables and legumes, and little to no meat or other animal products.

Yet a recent series of articles in the Annals of Internal medicine calls that into question, claiming that there isn't enough evidence that less meat improves health. The backlash from the nutrition community has been swift, calling the studies flawed, and even requesting that the journal retract them.

While the new studies have grabbed headlines, the bulk of the research still supports eating less meat, says Mayo Clinic Healthy Living Program dietitian Angie Murad, RDN, LD. "There is a lot more evidence to move towards a plant based diet," she says.

Here's how a plant-based diet can help fight cancer — and what one looks like.

Thinking beyond meat

For many Americans, meals center around the meat. After all the Department of Agriculture reports that 222 pounds of meat are sold per person per year in the U.S.

But when researchers asked nearly 70,000 volunteers about their diets, then tracked them over time, they found lower cancer rates among people who didn't eat meat at all.

In fact, vegans — those who don't eat any animal products including fish, dairy or eggs — appeared to have the lowest rates of cancer of any diet. Next in line were vegetarians, who avoid meat but may eat fish or foods that come from animals, such as milk or eggs.

But it's important to note that eating meat — or not — wasn't the only difference between people who did or didn't get cancer. People diagnosed with cancer also had a higher body mass index, were less active and were more likely to have smoked.

Plant-based cancer prevention

The natural question: Are vegetarians more resistant to cancer because they don't eat meat? Or is it because of what they eat instead?

It's true plant-based foods, such as fruits, vegetables, legumes, nuts and whole grains, are packed with nutrition. And research has also shown that eating lots of them is linked with lower cancer rates.

An explanation: Plants produce many phytochemicals (literally, plant chemicals) that may protect cells from damage. Phytochemicals have many beneficial effects, including that they are anti-inflammatory, says Murad.

Another way plant-based foods may prevent cancer is by boosting fiber consumption. Young women who ate the most fiber-rich diets were 25% less likely to get breast cancer later in life, a study found. Other research finds that each 10 grams of daily fiber could lower the risk of colorectal cancer by 10%.

Or it could be even simpler still, suggests Murad. "When people eat a more plant-based diet, they naturally consume fewer calories, which helps to maintain a healthy weight." Vegetarians are less likely to be overweight, a known risk factor for some types of cancers.

The impact of meat on cancer rates

If it's all about loading up on phytochemicals and fiber, meat lovers may be tempted to have their steak, and a salad too. But research also suggests a link between meat and cancer.

In one review each additional 3.5 ounces of red meat a day raised the relative risk of colorectal polyps by 2%. Just half as much daily processed meat — such as deli meats or hot dogs — raised the risk by 29%.

So what's the problem with meat?

Eating more of it has been shown to increase the risk of dying from all causes. A key reason: Chemical compounds created when red meat is cooked are thought to be cancer causing. Compounds in processed meat also seem to contribute.

The less red and processed meat you eat, the better your health. If you don't want to go cold turkey, Murad says a good guideline is to eat no more than 12 to 18 ounces of red meat or processed meat a week. Three ounces is about the size of your palm.

Finding a balance

To shift to a more plant-based diet that you'll want to stick with, Murad suggests making gradual changes. Some ways to do it:

  • Experiment with meatless meals. Set a goal of trying one new meat-free recipe a week. And there's more to "Meatless Monday" than alliteration, according to Murad. You may be more likely to stick with a new healthy habit at the beginning of the week.
  • Use beans for bulk. Decrease the overall amount of meat in some recipes by increasing the amount of beans, lentils or vegetables. A bonus: "Those types of foods fill more space on your plate, and we often eat with our eyes, so you don't feel like you're being deprived," says Murad.
  • Treat meat like a condiment. Instead of using meat as a main dish, use just a little bit for flavor. "At our Mayo cooking classes, Chef Jen Welper has guests cut turkey bacon into very small pieces and sprinkle them over a pita pizza," says Murad. You get the flavor in every bite without using much.

Eating a plant-based diet doesn't have to be all or nothing. "Small changes can have a big impact," Murad says.

Oct. 30, 2019 See more In-depth