Tom pushing through dumbell burpees (thanks to CrossFit Verve for this fun exercise)
It can be tough to define "fitness". Is it the ability to do long-duration cardio? Is it the ability to bench press 500 pounds? There are many definitions. Once defined, it can also be pretty tough to figure out how to be fit. Check this out. This "World Class Fitness in 100 Words" is from Gregg Glassman, founder of CrossFit:
Eat meat and vegetables, nuts and seeds, some fruit, little starch and no sugar. Keep intake to levels that will support exercise but not body fat. Practice and train major lifts: Deadlift, clean, squat, presses, C&J, and snatch. Similarly, master the basics of gymnastics: pull-ups, dips, rope climb, push-ups, sit-ups, presses to handstand, pirouettes, flips, splits, and holds. Bike, run, swim, row, etc, hard and fast. Five or six days per week mix these elements in as many combinations and patterns as creativity will allow. Routine is the enemy. Keep workouts short and intense. Regularly learn and play new sports.
Does your diet and workout look anything like this?