Put it this way - if grains were cars, whole grains would be a deluxe model Mercedes with all the bells and whistles while refined grains would be a basic model car. Both get you from A to B, but the Mercedes is just that cut above.
The “bells and whistles” in whole grains are the many nutrients, including phytochemicals and antioxidants, that are missing from refined grains. These nutrients help to fight a number of diseases including:
Studies show that people who regularly eat whole grains reduce their risk for all of these diseases. Research also suggests that whole grains may be even better than fruits and vegetables as a source of key nutrients for fighting disease.
In contrast, refined grains lack many of the nutrients found in their whole grain cousins. That’s because refining normally removes the grain’s healthy bran and germ, leaving only the endosperm. This results in a loss of many key nutrients including much of the fiber. Some manufacturers of products which contain refined grains, such as white bread, try to compensate for this by enriching their products with vitamins. Whilst choosing these products is better than choosing unenriched products, it’s still far better to choose the whole grain product if you’re after the maximum amount of nutrient “bang for your buck”.
Next time you're at the grocery store choosing between white rice and brown rice or white bread and whole-grain bread, take the Mercedes.