Fruits and vegetables contain a variety of vitamins, minerals, antioxidants, and phytochemicals that protect the body. Building a plant-based (or vegan) diet from fruits, vegetables, beans, and whole grains can help prevent some cancers and improve the survival rates of people who have cancer.

Eighty percent of cancers are due to factors that have been identified and can potentially be controlled, according to the National Cancer Institute, and at least one-third of annual cancer deaths in the United States are due to dietary factors, according to the American Cancer Society. Much of our risk for colon, breast, and prostate cancer, among other types, is nutrition-related.

While vegan diets can help fight cancer and other diseases, consuming animal products—meat, eggs, dairy products—and other fatty foods can contribute to cancer risk.

Numerous research studies have since shown that cancer is much more common in populations consuming diets rich in fatty foods, particularly meat, and much less common in countries with diets rich in grains, vegetables, and fruits. The reason? Food affects the action of hormones in the body and the strength of the immune system.

Plant-based diets can be helpful in preventing cancer and cancer recurrence because they are generally low in fat and high in fiber. Fat has many effects within the body. It increases hormone production (and may raise breast cancer risks) and it stimulates the production of bile acids which have been linked to colon cancer.

The average diet in the United States is about 37 percent fat from calories. The National Cancer Institute suggests that people lower that number to 30 percent; however, studies have shown that fat intake should be well below 30 percent to have an anti-cancer affect. Ten percent or less is the most effective.

Fiber is essential for preventing disease and staying healthy. Animal products contain no fiber, but diets based on fiber-rich, plant-based foods provide plenty of this important nutrient. Fiber helps move food more quickly through the intestines, helping to eliminate carcinogens and potentially harmful hormones.

In the United States, the average daily fiber intake is 10 to 20 grams per day. Experts recommend 30 to 40 grams per day for cancer prevention and survival. The best sources of fiber are whole grains, beans, peas, lentils, vegetables, and fruits. Foods that are closest to their natural state, unrefined and unpeeled, are highest in fiber.

The United States and other Western nations whose diets are based upon animal products have the highest rates of colon cancer.

Eating a variety of vegetables is important because vegetables contain so many cancer-fighting substances. Carotenoids, the pigment that gives fruits and vegetables their dark colors, have been shown to help prevent cancer. Beta-carotene, present in dark green and yellow vegetables, helps protect against lung cancer and may help prevent cancers of the bladder, mouth, larynx, esophagus, breast, and other sites.

Vegetables such as cabbage, broccoli, kale, turnips, cauliflower, and Brussels sprouts contain flavones and indoles, which are thought to have anti-cancer effects. Vitamin C, found in citrus fruits and many vegetables, may lower risks for cancers of the esophagus and stomach.

Studies of vegetarians show that death rates from cancer are only about one-half to three-quarters of those of the general population. Breast cancer rates are dramatically lower in countries such as China and Japan, where diets are typically based on rice, vegetables, and bean products, with very little use of meat, dairy products, or oily foods. When people from those countries adopt a Western, meat-based diet, their breast cancer rates soar.

By Jennifer K. Reilly, R.D.
The Cancer Project