First, let's look at the item itself.
Condensed.
Therefore,
-20% eating time.
No healing from the Sandvich. (I'll change it if you don't like it.)
However, it's got upsides, too.
+10% recharge time.
The effects are active for half a minute. (30 seconds.)
Let's take a stat jab.

Level (1-100) Condensed Food Item.
MINICRITS ARE DEALT BY THE PLAYER WHO CONSUMES!
-20% eating time.
+10% recharge time.
No healing from the Sandvich. (I'll change it if you don't like it.)
Effects of the item last 30 seconds.
Overheal effect varys, and happens if the player picks up medpack(s) while effects are active.
Small adds 10% overheal. (it's small.)
Medium adds 25% overheal. (Medium.)
Large (very rare on some maps) adds 50% overheal.
Resupply doesn't count, neither does other kinds of healing. (mad milk, medics, etc.)

If an enemy picks it up, he deals 5% more damage to your team.
If an ally picks it up, he deals 5% more damage to the enemy team.
To sum it up:

Level (1-100) Condensed Food Item.
-20% eating time.
+10% recharge time.
No healing from the Sandvich. (I'll change it if at least 10 people complain.)
Overheal effect is added if the player picks up a medkit while effects are active.
Enemy picks up: 5% more damage is dealt by that player.
Ally picks up: Ally deals 5% more damage, as well as the overheal effect.
Anyone eats: Minicrits are dealt by the player who consumed.

(Description Idea: Help Vladmir Bananas defeat Poopy Joe!)