Exercise creates microscopic damage to the muscles cells which are made up of proteins. Consuming protein after a workout helps repair muscle damage. The ultimate goal is to create stronger, bigger and fitter muscles.
Currently, the recommended daily allowance of protein is 0.8 grams of daily protein per kilogram of body mass (1 kilo gram equals 2.2 pounds). For example, a 150 pound (68 kilograms) adult that works out requires 55 grams of protein per day. However, some experts recommend, 1.5 to 2 grams of daily protein per kilogram for optimal muscle growth. In the example above, the same 150 pound adult, would require 102 to 136 grams of protein per day.
So how long after your work out should you consume protein for maximum benefit, prevailing school of though is within 1 hour after your workout. However, recent studies suggest benefit up to 2 to 3 hours post workout.