The Office of Disease Prevention and Health Promotion warns against relying on juice as your sole source of nutrition. This kind of diet won’t give you enough protein or fiber to maintain muscle mass and keep you feeling full. Here's what nutritionists have to say: "Juicing alone won’t fix an unhealthy diet, it’s also important to cut out the junk foods and eat more lean protein sources, dairy or calcium sources, whole grains, and more fruits and veggies."