When CJ is hungry, a message will appear onscreen alerting you to his need for some chow. If you choose to ignore this missive, his energy level will start to decrease, and a host of other bad things will begin to happen.
As with the previous GTA games, you can expect the food service establishments in San Andreas to mirror real-life locales--but with satirical twists.
To wit, three of the franchise restaurants in the game are Cluckin' Bell, Well Stacked Pizza, and Burger Shot.
you will become fatter and fatter, resulting in the unpleasant sight of CJ bulging out of his clothes. Your tough saunter will become a waddle, and you won't be able to put your arms by your side.
If you let CJ reach obese proportions, expect the extra pounds to impact everything he does that involves physical exertion, such as lifting, climbing, swimming, cycling, running, and so on
plan on being taunted and not having much success with the ladies if you're too tubby
The key thing to note is that skinny doesn't necessarily mean fit. You'll have to manage CJ's development of fat and muscle to have him be in optimal physical condition.