Most high-level competitive bodybuilders have pretty puffy, flabby physiques outside of competition season due to a combination of juicing and the caloric demands required to pack on as much muscle mass as they want to. The diets they go on 6 weeks out from comps are pretty crazy too shed all that fat and stop the extreme water retention they want during hypertrophy phases.
Juicing for pure strength shouldn't make anyone fat. Look at the Bulgarian Olympic lifters from the 80s. Plus, sprinters, and other such athletes are good example of just how slim juicers can stay, as it mostly depends on diet and goals whether juicing causes you to get fat or not. Most cases of this I have witnessed, were with people not reducing their caloric intake enough when they got off the juice.