There is free body armour available at the police station but to get it you need to go in unarmed. If you try and enter the police station armed you will automatically get a 'Wanted' star which will make getting it difficult.
You can easily raise your Wanted level by getting into trouble. If you need to decrease it, especially when it reaches the higher ratings you need to try and get to a safe house. Changing your appearance will remove the Wanted Level entirely.
Keep eating at any of the restaurants which can be found scattered around the city to get fat or if you want to gain some muscle do workouts at the different gyms or at the Muscle Beach location in Santa Maria.
Stop at any of the fast food restaurants that are scattered about the game when you need to regain lost strength, you can also regain lost strength by getting arrested but if this happens you will lose some cash.