There are a lot of reasons people choose vegan or vegetarian lifestyles, including religion, taste preferences, health issues or concerns about animal ethics or environmental sustainability, among others.
On average, vegans had a childhood IQ score that was nearly 10 points lower than other vegetarians: mean (SD) IQ score 95.1 (14.8) in vegans compared with 104.8 (14.1) in other vegetarians (P=0.04), although this estimate must be viewed with caution as only nine participants were vegan.