Eat them, already! - Scientists are zeroing in on just which fruits and vegetables fight cancer -- and which ones don't.

Fruits and vegetables are packed with vitamins, minerals, antioxidants, fiber and scores of phytochemicals that scientists are just beginning to understand, and studies have shown that people who eat more fruits and vegetables have a lower risk of heart disease, stroke, diabetes -- and some kinds of cancer.

Since its inception in 1991, the 5 A Day campaign, led by the National Cancer Institute and Produce for Better Health Foundation, has upped its daily recommendation to as many as 13 servings under a new campaign name.

And in bestselling health books and the popular press, the talk of fruits and vegetables is sometimes breathless. Pomegranate juice is a "miracle medicine"! Blueberries are "the super berry"! Kale can keep you alive! Tomatoes for life everlasting!

Eat or drink this produce, we are told, and the powerful clout of super-antioxidants and tumor-fighting chemicals they contain will bash that cancer before it gets going.

In fact, the anti-cancer clout of fruits and vegetables is nuanced and complex, and a story still evolving in labs across the country. At times the science has proven to be murky. Small studies that rely on what people remember of their diets from years past often find a strong preventive effect of eating lots of fresh produce.

But recently, some large population studies -- which follow tens of thousands or hundreds of thousands of people for years -- have reported weak or nonexistent connections between produce and cancer. Scientists are still trying to understand these seeming contradictions.

This much seems to be true: When it comes to fighting cancer, the power of produce will depend on who -- genetically -- you are, the variety of vegetables or fruits you select and even whether you cook them or not.

You also have to eat the whole thing. Sorry, no shortcuts with pills containing lycopene, beta carotene or vitamin C.

Not all fruit and vegetables, it seems, are equal when it comes to their cancer-fighting capacity. Some of the strongest evidence is for cruciferous vegetables, such as broccoli, cauliflower and kale. Dark, leafy greens such as spinach and chard, cooked tomatoes, apples, pears and citrus all show cancer-protective effects in some large studies.