There is no better writer than Michael Pollan (The Omnivore’s Dilemma) at keeping the big picture in focus when trying to determine what it is we should be eating. The cover of his New York Times bestseller, In Defense of Food sums it up nicely:
AN EATER’S MANIFESTO:
EAT FOOD, NOT TOO MUCH, MOSTLY PLANTS

Pollan states that we are in an age of ever-increasing focus on nutrition and exercise, yet we are more nutrient-deprived and overweight than prior generations. His guidelines are straightforward: don’t eat anything your great-grandmother wouldn’t recognize as food; don’t eat food that contains ingredients whose names you do not recognize; and don’t eat food that makes health claims on its packaging. Get out of the supermarket when options like farmers’ markets exist. Cook if you can, eat meals (preferably not alone), and focus on better quality rather than greater quantity. Eat like you are Greek, French, Japanese, Indian, or Italian. Don’t skip eating the leaves from the plants.  Remember to think of what your dinner dined upon (corn-fed or corn-finished diets are designed to fatten many animals). And try not to look for the magic “bullet” or single food that will promote longevity or weight loss–nutrition and health, according to Pollan, are more the product of whole dietary patterns working together over time.