Eating your fruits and vegetables is the second most important strategy for preventing cancer after quitting smoking, says the American Cancer Society. Yet the average American consumes only one serving of fruit and one of vegetables, out of the five to nine recommended by USDA dietary guidelines. Many people rely on vitamins to cover the nutritional gaps.

Unfortunately, most supplements don’t match Mother Nature. Researchers at Florida State University have found that few vitamins contain phytochemicals, naturally occurring disease-fighting substances found only in fruits and vegetables. Plus the vitamins and minerals in foods are attached to elements called cofactors, without which they couldn’t be carried into the cells, as 1999 Nobel Prize winner Günthe Blobel, PhD, discovered.

Some experts believe that in addition to eating fruits and vegetables, we should take supplements containing enzymes found naturally in foods, such as protease, lipase, amylase and cellulase. These beneficial substances act as antioxidants, repairing damaged cells and stimulating the immune system, says holistic healer Roni DeLuz, PhD. However, such supplements are more expensive than those without enzymes, and they lack cofactors, so their benefit may be minimal. To get those cofactors, you still have to go to the source: fruits and vegetables.