So if that's the case, why is it important to eat such whole foods?
Before I give you an answer, I want to point out the trap that you may have fallen into by even considering this question. If you've been reading this blog for some time, then at this point you should realize that when it comes to your health, X usually does not cause or prevent Y.
Yes, there are some notable exceptions like cigarette smoking causing lung cancer, trans-fats causing heart disease, etc. but it's almost never so simple. True, we also know that sufficient levels of Vitamin A prevent night blindness, of niacin prevent pellagra, of Vitamin C prevent scurvy, etc. In other words, there are known cause and effects for certain diseases, but it's usually not one thing alone that causes the major killers such as heart disease, cancer, etc.
Why? The human body is a very complicated machine that is usually able to handle many imperfections (like autoimmune diseases, etc.) and environmental assaults (unhealthy foods, etc.) before it breaks down and stops working completely. It has many built-in mechanisms such as the immune system, the complement system, etc. that fight to fix problems before they wreak havoc.
Even in the case of really harmful things like smoking, not everyone develops lung cancer, one of the known consequences. Sometimes smokers die from the heart damage that smoking does and sometimes they die from something completely unrelated. (Many smokers who don't develop cancer from smoking do develop other lung diseases like emphysema and Chronic Obstructive Pulmonary Disease (COPD), the fourth highest killer of Americans.)
The point here is that it would be a mistake to think that anything, including fruits and vegetables, considered in isolation would prevent major diseases such as heart disease, the leading killer of Americans, and cancer, the second leading cause of death.
It is the sum of the parts that ultimately make a difference. If one eats lots of fruits and vegetables but simultaneously eats lots of processed sugar and other known carcinogens, the fruits and vegetables are unlikely to yield a high preventive effect.
So now let's come back to my question of why it is important to eat fruits and vegetables in regards to cancer.
The answer is that while no study has distinctly proven a cause and effect relationship between the amounts of fruits and vegetables one consumes (once above the deficiency threshold and below the toxicity level) and the development of cancer, there are certain factors that have proven to be strong risk factors for cancer development. One is weight. Overweight and obese people appear to have a markedly increased risk for development of a variety of types of cancer affecting both men and women. It is also a strong risk factor for cancer recurrence. For most people, their weight is a direct result of the types of foods they eat. People who typically eat more fruits and vegetables usually eat less processed foods like breads, crackers, pasta, etc. and weigh less. (See my previous posts 'Why You Get Fat?' and the two part 'Why You Stay Fat?' for a more exhaustive discussion.)
As I previously wrote about a close relative that was recently diagnosed with cancer, I have taken a keen and deeper interest in the subjects of cancer prevention and survivability so that I may offer this relative the best guidance.
After review of hundreds of cancer prevention studies, I have reached some very tentative conclusions.
Fruits and vegetables alone (and clearly supplements including vitamins, minerals, antioxidants, etc. naturally found or synthetically produced to mirror such chemicals) do not alone prevent cancer.
However, as part of an otherwise healthy lifestyle that includes avoidance of known carcinogens such as smoking, drinking lots of alcohol, being overweight, exposure to environmental hazards such as asbestos and numerous other substances and chemicals such as acrylamide that develops on the surface of french fries during the frying process, nitrites used to preserve cured meats, certain food dyes, pesticides, and other chemical additives, etc., eating fruits and vegetables is likely to cut down one's risk of both developing cancer and dying from it. As I previously wrote, the risk of men developing cancer is 1 out of 2 and of dying from it is 1 out of 4. For women, the numbers are slightly better with the risk of developing it being 1 out of 3 and of dying of it being 1 out of 5.
Cancer remains mostly a disease of random mutations instead of genetics. What causes these mutations, why some get it versus others, and why some survive the exact same cancers while others die from them remains an issue of scientific debate. While science continues to try to figure it out, do yourself a favor and shift the odds in your favor. Substitute fruits and vegetables in place of processed foods, in addition to making many other known healthy lifestyle choices such as regular exercise, getting proper sleep, etc. By doing so, you will give your body every opportunity to function at the optimal health level and to continue functioning for many more good years.