You can even make the argument that fruit juice is WORSE for maintaining a healthy weight than full-sugar soda. The soda has the exact same amount of calories in pure sugar, but it's carbonated so at least it's a little more filling.  Plus fruit juice has the "fake health effect" so hams feel like they're making a "healthy choice" when they consume it so they're more likely to guzzle down a bunch and reward themselves with junk food later for being "good" earlier. If a ham drinks a soda, they at least know it's not helping and might actually compensate later by exercising more or eating a little less (not likely but possible).