You can't go wrong here. A good protein shake will increase blood flow to your muscles, replenish energy stores, and make it easier for your body to process and use carbohydrates during the hours that follow your workout. Kumai suggests a quality whey protein: "Whey protein has many uses, including improving athletic performance and assisting with weight maintenance," she says. If you're not into whey, she also suggests rice, pea, and hemp protein.
No time to blend your own post-workout beverage? Try a grab-and-go drink, like the Protein Berry Workout Smoothie from Jamba Juice. It packs 20g of whey protein, along with whole fruit and soy milk.