While it is common to see scientific studies on how health can be improved by using certain, particular supplements of vitamins and minerals it is not the same for the real McCoy. How true? Ask yourself and do a goggle search (or a PUB Med or any advanced search of scientific articles) about how many times you see a study--any study--on a particular fruit or vegetable that comes out proving some health improvement. Not a group, but a particular fruit or vegetable. And proof of health, not disease (this is an important distinction).
We are talking about real science here not just made up stuff from some science nut or health nut. And we are talking about real fruits and vegetables like a particular apple or broccoli as opposed to a group of fruits or vegetables. In other words we are talking about something very concrete and not at all abstract--this is where real scientific study comes in very handy: such study is not abstract or it is not science. And, importantly, if I can prove it and you cannot, it is not scientifically provable. Period.
How many? Which vegetable? Which fruit?
There are plenty of promoters of eating fresh fruits and vegetables and many of them provide solid credentials like the Harvard, Tufts, Eat 5 a day, and so on (for a really good goggle search try vegetables and health or fruits and health).
For example, the Harvard site cites the latest dietary guidelines that, "call for five to thirteen servings of fruits and vegetables a day, depending on one's caloric intake. For a person who needs 2,000 calories a day to maintain weight and health, this translates into nine servings, or 4½ cups per day." The citation for this is The USDA, the U.S. Department of Agriculture. It is a helpful abstraction but not a particular guide to particular fruits and vegetables and how they can promote your health.
But most of what these prestigious institutions promote is air--no scientific studies demonstrating the health effects of a single fruit or vegetable could be found on the Harvard site, not one. True, it's nice air, but air nevertheless.
Now we are not talking about the genuine research on fruits and vegetables like this one listed in Pub Med, "Electron beam and gamma irradiation effectively reduce Listeria monocytogenes populations on chopped romaine lettuce", (J Food Prot. 2006 Mar;69(3):570-4, for those who need to know) . This kind of research is not after the health promoting effects of eating, in this case, romaine lettuce. And it does not pretend to be anything other than what it is.
Of course sites promoting the health benefits of eating of fruits and vegetables could be hiding the scientific studies and don't want to bother their visitors with all those numbers and scientific names for turnips or plums. Or farmers who grow the really good stuff and how to buy them.
I remember a study concerning folate and green leafy vegetables and some kids on an island in the South Pacific. The study, a genuine scientific study, had to be halted because the scientists found that the children in the study could not get enough folate for their diets from the fresh vegetables because the vegetables themselves were deficient. So the study stopped because, ethically, depriving the children's diet of this essential ingredient could hurt them--especially when the science proved the children would be deficient on a natural diet. So much for the health promoting benefits of this entire group of vegetables--and I have not seen another study to refute this single isolated, particular controlled scientific study on green leafy vegetable and exactly how they promote health in humans.
So how do you know if the fruits or vegetables you eat can really promote better health? Simple answer is you don't. But then again, if you stopped eating fruits and vegetables what would happen? Could be all those diseases they write about in Pub Med and cited by the Tufts nutritionists and become the cover story about our fat nation for Time Magazine: eat your fruits and veggies and stay healthy or until we know, for sure, something different.
