Food works on 2 levels, there is the Hunger Bar and Saturation bar. The saturation bar isnt visible in game, but think of it as a 2nd hunger bar above your normal hunger bar, thats exactly what it is.

Now then, eating food you add both Hunger and Saturation points.
Now for every full point of hunger you see actually equals 2 points of hunger. (20 points per bar)

Now doing specific actions adds to a 3rd variable called Exhaustion Level. Depending on what actions you do you add points to the exhaustion level. When the exhaustion level equals 4 points, your saturation or hunger level goes down 1 point and it starts all over again.

Now you may wonder well how many blocks can I travel on 1 hunger point? With my awesome math capabilities here are the results:
Walk/Sneak/Survival Fly: 400 Blocks
Sprinting: 40 Blocks
Swimming: 266.666 Blocks
Jumping (no walking): 20 Blocks
Sprinting + Jumping: 5 Blocks
Numbers Of Blocks You Can Break: 160 Blocks
Number Of Times You Attack A Mob: 13.333 Swings
Number Of Times You Take ANY Kind Of Damage: 13.333 Hearts

You may wonder well what if I had both food bars full? Well thats just 40 Times the previous results. Just for simplicity sake here are the answers:
Walk/Sneak/Survival Fly: 16,000
Sprinting: 1,600
Swimming: 10,666.666
Jumping: 800
Sprinting + Jumping: 200
Block Breaks: 6,400
Mob Attacks: 533.333
Any Kind Of Damage Received: 533.333

Basically the math formula is (1 / Action Taken) x 4 = Results
So for walking its (1 / .01) x 4 = 400