Intelligent children are more likely to become vegetarians later in life
A Southampton University team found those who were vegetarian by 30 had recorded five IQ points more on average at the age of 10.
Researchers said it could explain why people with higher IQ were healthier as a vegetarian diet was linked to lower heart disease and obesity rates.
The study of 8,179 was reported in the British Medical Journal.
Twenty years after the IQ tests were carried out in 1970, 366 of the participants said they were vegetarian - although more than 100 reported eating either fish or chicken.
Men who were vegetarian had an IQ score of 106, compared with 101 for non-vegetarians; while female vegetarians averaged 104, compared with 99 for non-vegetarians.
There was no difference in IQ score between strict vegetarians and those who said they were vegetarian but who reported eating fish or chicken.
Researchers said the findings were partly related to better education and higher occupational social class, but it remained statistically significant after adjusting for these factors.
Vegetarians were more likely to be female, to be of higher occupational social class and to have higher academic or vocational qualifications than non-vegetarians.
However, these differences were not reflected in their annual income, which was similar to that of non-vegetarians.
Lead researcher Catharine Gale said: "The finding that children with greater intelligence are more likely to report being vegetarian as adults, together with the evidence on the potential benefits of a vegetarian diet on heart health, may help to explain why higher IQ in childhood or adolescence is linked with a reduced risk of coronary heart disease in adult life."
Brainy Kids May Become Vegetarians
Intelligent children more likely to become vegetarian