Julie asked the question the other day about eating after a workout. This is known as the post-workout meal, and yes, it is important. In fact, it should be eaten consistently, within an hour after you workout.
Why is this important? Well lets review a little physiology. With strenuous exercise, the stress hormones, epinephrine and norepinephrine, are released and act on the the whole body, including the skeletal muscles. These hormones stimulate the breakdown of glycogen (linked carbohydrates that are stored in the liver and muscle) to use as energy. They also inhibit the release and breakdown of fatty acids from the fat cells. This is good, because fat metabolism is a slow and inefficient process. Also, with powerful muscular contractions the contractile proteins are damaged. These proteins need to be repaired.
So after the body has endured the rigors of your exercise training, it needs to return to its rested state (with restored energy stores and repairs made). The hormones that synthesize glycogen and build contractile proteins are stimulated by hormones such as insulin, growth hormone, and testosterone after the workout is completed. Blood sugar is taken up rapidly, along with amino acids into the muscle cells. This is one reason why regular exercise, even strength training is helpful for diabetics. There is an increased energy need, hence an elevated metabolism.
The food you eat within the "post-workout window" gives your body the energy and building blocks it needs to fully recover. The reason why there is a time-urgency is that the hormones and enzymes peak at this time. As you get further beyond this 'post-workout window' their activity levels decline.
What food should you eat during this time? Well this is the time to eat foods that are digested rapidly- just the opposite of all of your other meals. You need protein and simple, quick absorbing carbohydrates (sugars). You don't want fat or complex carbohydrates. A typical meal (adjust for total Calories) would consist of 20 grams of protein, 40 grams of carbohydrates, and no fat.
I am sure someone will ask "what if I want to lose body fat?" The answer is definitely Yes! Cut Calories with other meals, not your 'post-work' meal.