From Dr. Fuhrman's book Eat to Live:
We are on the verge of a revolution. Substances newly discovered in broccoli cabbage sprouts sweep toxins out of cells. Substances found in nuts and beans prevent damage to our cells' DNA. Other compounds in beets, peppers, and tomatoes fight cancerous changes in cells. Oranges and apples protect our blood vessels from damage that could lead to heart disease. Nature's chemoprotective army is alert and ready to remove our enemies and shield us from harm.
Hardly a day goes by when some new study doesn't proclaim the health-giving properties of fruits, vegetables, and beans. Unprocessed plant foods contain thousands of compounds, most of which have not yet been discovered, that are essential for maintaining health and maximizing genetic potential. Welcome to the phytochemical revolution.
Phytochemicals, or plant-derived chemicals, occur naturally in plants (phyto means "plant"). These nutrients, which scientists are just starting to discover and name, have tremendously beneficial effects on human physiology. The effects of our not consuming sufficient amounts of them are even more astounding--premature death from cancer and atherosclerosis.
Eating a wide variety of raw and conservatively cooked plant foods (such as steamed vegetables) is the only way we can ensure that we get sufficient amount of these essential health-supporting elements. Taking vitamin and mineral supplements or adding some vitamins to processed foods will no prevent the diseases associated with eating a diet containing a low percentage of calories from whole natural foods.
Scientists cannot formulate into pills nutrients that have not yet been discovered! If the pills did contain sufficient amounts of all the phytonutrients and other essential substances, we would have to swallow a soup bowl full of pills and powders. To date, researchers have discovered more than ten thousand phytochemicals. No supplement can contain a sufficient amount. Thankfully, you can get all these nutrients today by eating a wide variety of plant-based foods.
Please bear in mind that I am not against nutritional supplements. In fact, I recommend various supplements to many of my patients with various health problems, and a high-quality multivitamin/multi-mineral to almost everyone.
I do not recommend that most people consume supplements containing vitamin A, isolated beta-carotene, or iron, as there are risks associated with excess consumption of these nutrients. The point to be emphasized is that supplements alone cannot offer optimal protection against disease and that you cannot make an unhealthy diet into a healthy one by consuming supplements.