Diets can turn anyone into a crab, due to the discipline and restraint they require, along with the body's metabolism changing to accommodate for a smaller intake of food. But changing one's eating habits and lifestyle altogether, such as eliminating all meant, dairy and animal products to become a vegan, can really cause a disruption in more ways than one.

Just ask Justin Bieber and Selena Gomez! The Biebs reportedly went vegan and as his consumption of animal-derived food stopped, his mood plummeted.

Apparently, The Biebs tried to adopt veganism, a dietary lifestyle employed by his mentor Usher, but it didn't agree with him and his lack of proper eating habits turned into a jerk, according to his lady love Gomez.

“She had encouraged the health kick, but told him to drop it. She said that being vegan turned Justin into a jerk," a source told the Star (quotes courtesy of SugarScape.)

How did veganism turn the 'As Long as You Love Me' singer into a jerk?

“His mood took a major nose dive — he was such a brat," the insider continued. "Soon everyone was begging him to just eat a steak! Justin ordered a tofu steak and tempeh tacos from Real Food Daily in L.A. and was really grossed out. He made a big show of spitting out the food and making gagging noises.”

If the last part is true, maybe The Biebs should have further researched veganism before attempting it.

And it seems like he body is already reacting to his change in diet, as Bieber recently lost his lunch on stage, citing "milk" as the reason for his embarrassing act.

Watch the Justin Bieber 'As Long as You Love Me' Video