Scientists at the University of Southampton in England studied the diet of more than 8,000 thirty-year olds whose IQs had been measured when they were ten. The results showed a positive correlation between IQ and the odds of being a vegetarian.

The leading scientist Dr. Catherine Gale explained that people who are more intelligent as children, and who will obviously keep that intelligence when they are 30, are more likely to be vegetarians at that age than those that are less intelligent. This is consistent with other studies showing that people who are more intelligent tend to eat a healthier diet and exercise more. 

Source: http://www.reuters.com/article/healthNews/idUSL1452462620061215