Good nutrition is of course a fundamental for good health, and we are fortunate in Marin to have access to so much excellent food of every kind.
As in most of America, our problem is having too much food, but unlike most areas, we have a great choice of genuinely nutritious foods rather than having to make our diets out of mostly empty calories or worse.
I am a big fan of Michael Pollan, author of "The Omnivore's Dilemma", "In Defense of Food" and "Food Rules". I think he has it right when he boils his dietary advice down to the pithy sentence "Eat food, not too much, mostly plants." By "food" he means something that actually lived and grew rather than something synthesized or processed.
I don't believe you need to be a vegetarian to be healthy, but if vegetables cover half your plate, a grain or legume (beans, lentils, etc.) a quarter and a protein source (fish, organic poultry, beef, pork, tofu) the other quarter you are on the right track to eating for both a healthy and long life. Eating vegetarian or vegan can also be very healthy if you pay attention to protein sources.
Even if you eat well, when we do laboratory testing to look at people's micronutrient needs (vitamins, minerals, antioxidants, and essential fatty acids), we rarely find people who have no additional needs beyond what they get in their diets. Because individual vitamin needs can vary by as much as 50-fold, I believe that biochemical testing is a useful addition to good diet to determine optimal intake levels of these critical nutrients.