Eating in the middle of the day (lunch) always makes me sluggish, so I eat a large breakfast, including fruit of juice, cereal, yogurt (on the cereal), and a couple of strong cups of coffee. The carbs and caffein get me running and are enough fuel for the day, and I don't eat again until dinner. Use your lunch hour for whatever else you can get done.
I don't know if that's the only reason, but I'm, 60, 6' 2", about 185 lbs, and healthy, as far as I know.
