here\'s the low down
Most protein bars will have about 300kcal, and 25-30g of protein. The protein won\'t give you energy (well it can, but only when you have a depletion of carbs and cortisol coverts the protein to glycogen, but I won\'t get into that) What will give you energy is the simple carbs in most protein bars, there\'s usually about 20-30g of simple sugars in them, and that\'ll give you quick energy.
As for the protein, I use them as a MRP (meal replacment) when I can\'t get ahold of some good whole food. If you already have a diet where you get adequete amino acids to support cellular synthesis and cell replacement (muscle building and the replacment of dead cells) then the extra protein will be converted into glycogen (the energy for muscles) and if not used it like carbs will be stored in adipose tissue as fat. So the readers digest version is if you already take in around 1.5-2g of protein per kg of LBM you probably don\'t need much more, thus a protein bar won\'t help you much.....EXCEPT, directly after working out because the simple carbs will stop catabolism (eating of muscle by the body) and will start anabolism. The protein will help because your body will be in protein synthesis and will be hungry for the amino acids.