Does the hunger meter decrease at a constant rate?

Question

In Minecraft 1.8 there is a new hunger meter that decreases over time.

Does this meter decrease at a fixed rate, or do certain activities like mining or sprinting cause it to decrease faster?

Answer 1

Minecraft now basically counts your calories. Each action takes a toll on your body; for example:

• 1 meat icon = 800 meters walked (i.e. walking 1 meter costs 1/800th of a meat icon)
• 1 meat icon = 320 blocks broken
• 1 meat icon = 80 meters sprinted
• 1 meat icon = 40 jumps
• 1 meat icon = 20 sprint jumps

However, meat icons only tell half the story. Eating food does not only replenish the visible health bar, but also an hidden 'food saturation' bar, and both max out at 20 points (a meat icon being worth two points). Actions drain "saturation points" before "food points."

Eating adds to both, but any saturation point in excess of your food points will be discarded. For example, a golden apple will give you 10 food points and 20 saturation points, but eat that with an empty stomach and you'll only reap two thirds of the benefit (0|0 + 10|20 = 10|10).

This is why the food bar does not go immediately down as you start playing: you're consuming your saturation points.

Foods that will give you full benefits every time (because they add more food points than they add saturation points) are raw meat, watermelons, apples, cookies and cake. More processed food, such as mushroom stew, cooked meat and golden apples will need at least a few meat icons to give you the full effect.

An additional note on rotten flesh. Food poisoning takes 15 points slowly; rotten flesh gives you 4|0.8 immediately. If you want to get any benefit at all, you'll want to eat 4+ pieces in quick succession.

More information here.

Answer 2

Mining blocks and sprinting both augment the speed at which the hunger meter depletes. The variable in Minecraft's code that controls how quickly your hunger decreases is foodExhaustionLevel. Every time you do a certain action, foodExhaustionLevel increases by a certain amount, and if it hits 40.0, 1 point will be subtracted from foodLevel (the visible hunger bar) if foodSaturationLevel is 0. (foodSaturation is a hidden variable that gets increased by different amounts when eating food, causing it to take a while before your hunger meter actually decreases.) Breaking a block increases exhaustion by 0.025, and sprinting increases it by 0.1 for every meter you run. (source)