Study: Diet & Lifestyle, Not Chemicals, Are The Largest Cause of Cancer

Dallas – More than half the natural chemicals in fruits and vegetables that have been tested cause cancer in laboratory rats and mice at very high doses. But according to a new study, people are far more likely to get cancer if they don't eat these foods.

The reason: apples, plums, carrots, celery and most other fruits and vegetables contain chemicals that help fight cancer, while naturally occurring carcinogens are present in such small amounts they are not likely to be significant causes of cancer, according to Bruce Ames and Lois Gold, co-authors of the study. Ames is a University of California at Berkeley professor who developed the "Ames test," used by scientists to determine whether a chemical causes mutations and is therefore likely to cause cancer in laboratory tests. Gold is the director of the Carcinogenic Potency Project at the National Institute of Environmental Health Sciences Center.

"Unbalanced diets, diets that are too low in fruits and vegetables for example, cause about a third of all cancer deaths," Gold said. "That's about the same number as die from cancer caused by smoking."

The study was published by the National Center for Policy Analysis. An earlier version appeared in the FASEB Journal.

According to the study, half of all chemicals scientists have tested – whether natural or man-made – have been shown to cause cancer when given to rodents at very high doses. Although only a few thousand have been tested, Ames suspects the ratio would also hold for the thousands of chemicals that have not been tested.

The study says naturally occurring rodent carcinogens have been identified in a long list of ordinary food and drinks including lettuce and tomatoes; potatoes and corn; broccoli, cabbage and peas; hamburgers; orange juice and chocolate milk; black pepper; wine and beer; and common tap water. Carcinogens have even been found in 49 percent of the prescription drugs that have been tested.

Although Ames developed a test for potential carcinogens, he's now concerned that the animal cancer test results are misleading, with cancer scare stories causing people to avoid items ranging from apples to soft drinks. In fact Ames isn't even sure that it's the chemical itself that actually causes cancer in laboratory experiments. "Evidence suggest that it is the high doses themselves, not the chemicals tested, that cause cancer," he said.

Our biggest risks of cancer come not from pesticides and food additives, but from ordinary lifestyle choices. The study says:

  • Smoking contributes to 35 percent of U.S. cancer cases.
  • Unbalanced diets account for about one-third.
  • Reproductive hormones contribute to as much as 20 percent of all cancer, and lack of exercise, obesity and alcohol intake influence hormone levels and increase risk.
  • Chronic infections cause about nine percent of cancer cases.
  • Cancer is also due in part to normal aging.

The study rebuts some common misconceptions about cancer. For example, human exposure to carcinogenic pesticides is minuscule compared to the background of exposure to carcinogens produced by nature. 99.9 percent of all pesticides humans eat are naturally produced by plants to defend themselves against fungi, insects and other animal predators. Americans eat about 10,000 times more natural pesticides per person, per day (measured by weight) than they consume of synthetic pesticide residues.

Not only are fears about man-made pesticides normally not justified, reducing their use may do more harm than good. The reason: organic fruits and vegetables are more expensive. And if higher prices cause people to buy less of the produce, there will be health consequences. The study reports that the quarter of the population with the lowest dietary intake of fruits and vegetables has roughly twice the cancer rate as the quarter with the highest intake. Abandoning the use of synthetic pesticides for organically grown crops, therefore, would likely cause cancer rates to rise.

As an example of what else can go wrong, consider the following case: In order to avoid man-made pesticides, plant breeders developed a new breed of insect-repelling celery. Yet this new "all natural" celery contained eight times the amount of natural carcinogens present in common celery.

The study also says that regulation of low level exposure to carcinogens does little to advance public health. The Environmental Protection Agency estimates the cost to society of environmental regulations at about $140 billion a year, more than $1,000 for every household in America. Much of this regulation is designed to protect people from low-level exposure to synthetic chemicals that cause cancer in rodents. It is not money well spent. Citing another study, Ames said the U.S. could prevent 60,000 deaths per year by directing the same dollars to more cost-effective programs.