In the 'You Are What You Eat' twin study, the vegan group lost more weight due to fewer calories, not the diet itself.

“the researchers provided the vegan twins with less calories well that will result in more weight loss”

“If you actually look at what they did, um they don't talk a lot about what they gave the omnivore group. They say it's a healthy omnivore diet, but they didn't really talk about it. And in the paper that they published, they said, "Oh, the study was so great, the vegans lost more weight." Well, if you look at the data, the vegans also ate less calories. They gave the vegans less calories, and then the vegans ate less and then they lost more weight.”