In the British Medical Journal (BMJ), Gale and her colleagues (2007) examined 8,170 people from the 1970 British cohort study. In this prospective study, childhood IQ was assessed at the age of 10; dietary status (vegetarian, vegan, or omnivore) was assessed twenty years later at the age of 30 by home interview. Taken collectively, 366 (4.48%) of the 8,170 people were vegetarian or vegan at the age of 30, an incidence similar to that (range = 1% - 9%; median = 4.5%; average = 5.25%) found recently in New Zealand, Australia, Ireland, Canada, Israel, Germany, the US, and the UK (Ruby, 2012). Of the 8,170 people, only 9 (0.11%) were vegans (i.e., had “ ‘gone the whole hog’, as it were” – Gale et al., p. 246) at the age of 30.

Women were 2.78 times more likely to be vegetarian than men, a result which is consistent with other studies. Possible reasons for this gender effect include neurological differences between men and women, the fact that women score higher on formal scales of empathy than men, and the fact that, in many cultures, eating meat is considered to be a “masculine activity” (Rozin et al., 2012; Ruby, 2012).

With respect to IQ at the age of 10, the 8,170 total subjects had an average IQ of 100. My re-analysis of this data indicates that, at the age of 10, vegetarians/vegans (combined) had higher IQs (average = 104.56) than did omnivores (average = 99.79) (p < 0.0001) over and above the negligible gender difference. Gale and her colleagues (p. 247) conclude that “Vegetarianism may be viewed by those of higher [childhood] intelligence as a healthier option that consuming meat,” a theory that is elaborated upon by Richards (2007) in an editorial in the same issue of BMJ.

However, direct causal inferences should be very cautiously drawn from this study for two reasons. First, both effect sizes (the vegetarian - gender association & the vegetarian – IQ association) are very small in magnitude, and correlation does not imply causation (i.e., just because many babies are born when storks nest on chimneys does not mean that a stork brought your baby). Second, the design of this (field) study is radically quasi-experimental – subjects were not randomly assigned to gender groups, IQ groups, or to dietary outcome groups. Many possible intervening, uncontrolled factors (e.g., “choice of newspapers [read], type of books read, preferred forms of entertainment” – [Gale et al., p. 247) may be more proximally related to the choice of a vegetarian lifestyle than gender or IQ per se.

(Free online article). Gale et al. (2007). IQ in childhood and vegetarianism in adulthood: 1970 British cohort study. British Medical Journal, 334, 245 – 248. http://www.bmj.com/hi...

(Free online article). Richards, M. (2007). Childhood intelligence and being a vegetarian (editorial). British Medical Journal, 334, 216 – 217. http://www.ncbi.nlm.n...

Rozin, P. et al. (October, 2012, in press). Is Meat Male? A Multi-Method Framework to Establish metaphoric Relationships. Journal of Consumer Research.

Ruby, M.B. (2012). Vegetarianism. A blossoming field of study. Appetite, 58(1), 141 – 150.

Interesting! Thanks for posting, Skip.