Ready to drink protein. Need a convenient protein drink ready to go? Grab a RTD and store at home, work or the gym bag. Protein is one of the most important macro nutrients for athletes, bodybuilders and those who are exercising to lose weight or gain lean muscle mass. While protein is found in meats, eggs and dairy products, people who work out regularly often have difficulty consuming all of the protein needed to support optimal results at the gym through diet alone. Protein supplements like protein powders, ready-to-drink protein shakes and protein bars can help you avoid deficiencies and ensure you're getting all of the protein that you need.