Oh, and as for what I eat...
I probably don't tend to pick the healthiest possible foods available, a lot of times I'll just pick better than average foods. I drink mostly diet soda and water (sometimes OJ too). I snack a lot and that is usually low salt nuts or sunflower seeds, pretzels, baby carrots, grapes, and random fruit/vegatables. Sometimes I'll have some baked potato chips for a snack too. For breakfast I eat dry cereal a lot (usually cheerios, not the heathiest, but not the worst either), sometimes I add blueberries for extra nutrition. If I feel like it I'll make a bacon/egg/cheese sandwich using low fat turkey bacon, 2% cheese, and whole wheat bread. I have a small frozen lean cuisine type meal for lunch usually. Then for supper I cook something that includes a healthy meat, some good veggies, lots of protein, and not too much fat.
When considering how healthy a food is I mostly look at calories (per serving, and serving size), protein, fiber, fat, carbs. I pay more attention to fiber than most I think. I also look at sodium and vitamins and minerals, but don't worry too much about those usually. I try to take a multi-vitamin too.