Answer:

Adequate calories and nutrients (particularly protein) for your height, weight, and activity level is necessary for muscle growth. Most American get enough protein in their diets.

As for after the workout, research is clear that eating carbs and protein within 30 minutes of your workout will help speed up your recovery time by replenishing glycogen stores and possibly increasing protein synthesis (there is some evidence that eating protein before your workout helps with protein synthesis, too). The guideline for carbs is to eat within 30 minutes of completing your workout and to have 0.7-1.2 grams of carbohydrate per kilogram of body weight (0.3-0.6 grams per pound). A large banana has 30 grams of carbohydrates. The guideline for protein is one gram for every 3-4 grams of carbs. Peanut butter has 9 grams of protein per 2 tablespoons. Yogurt is another good source of carbs and protein.