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In a post titled Why Vegetarians Are More Intelligent than Meat Eaters, evolutionary psychologist Satoshi Kanazawa claims:

Among the British respondents in the National Child Development Study, those who are vegetarian at age 42 have significantly higher childhood general intelligence than those who are not vegetarian at age 42. (Childhood general intelligence was measured with 11 different cognitive tests at three ages before 16.) Vegetarians have the mean childhood IQ of 109.1 whereas meat eaters have the mean childhood IQ of 100.9. The difference is large and highly statistically significant.

The Evening Standard discusses a similar study.

I am skeptical of this claim, so I searched for scientific data investigating this issue, but I couldn't find any solid scientific study conducted over long period or with bigger sample. The most articles I encountered were just speculations made people to support their own claim.

I found the following related research while searching:

  1. IQ in childhood and vegetarianism in adulthood: 1970 British cohort study

  2. Schooling, educational achievement, and cognitive functioning among young Guatemalan adults.

  3. Malnutrition can affect development of brain in early stages.

  4. The Hindu-CNN-IBN State of the Nation Survey 2006 : India

Is vegetarianism correlated to intelligence (as measured by IQ or similar methods)?

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    @GEdgar- In Britain, where the study was conducted, vegetarianism is (I think) mostly for moral reasons. In India it's for religious reasons. – PointlessSpike May 9 '16 at 7:30
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    After reading the article I'm sure you got it backwards. The question is "Are intelligent people more likely to go vegetarian?", not the other way around. – Agent_L May 9 '16 at 9:55
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    I wonder if this is true for any difficult, active lifestyle choice motivated by moral considerations, that people with higher IQ from childhood are more likely to make active decisions to change their lifestyle and are more likely to suceed in sticking to them? Trying to think of a suitable equivalent; maybe something like volunteering or supporting charities, or regularly giving blood – user56reinstatemonica8 May 9 '16 at 10:55
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    I think you need the study to control for income level. Perhaps vegetarian diets are more expensive than "eat whatever you can get" diets---maybe only people above a certain income level have the choice. And maybe income level is also correlated with IQ. Also, is the question supposed to be about "in Britain" or not? – GEdgar May 9 '16 at 17:18
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    Vegetarians have [...] IQ of 109.1 whereas meat eaters have [...] 100.9 Uhmmm... How exactly can both vegetarians and carnivores have above average IQ? Are there some flexitarians/vegans with really low IQ to balance this out? :P – fgysin reinstate Monica May 12 '16 at 13:26
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Unknown.

A 2019 meta-review The effects of plant-based diets on the body and the brain: a systematic review looks at the available evidence. The final sentence of the abstract is

Still, putative effects of plant-based diets on brain health and cognitive functions as well as the underlying mechanisms remain largely unexplored and new studies need to address these questions.

It goes on to discuss ways that a non-meat diet could be both positive and negative for cognition. However the larger studies seem to have focused on mortality and disease rather than brain function.

Regarding the first two articles in the question, both refer to the IQ in childhood and vegetarianism in adulthood: 1970 British cohort study, also mentioned in the question. This looks at a link between IQ in childhood and a tendency to vegetarianism in adulthood: it does not look at IQ in adulthood, so the vegetarians-are-more-intelligent titles of the Psychology Today and Evening Standard articles are misleading.

  • 2
    Given the combination of how vague intelligence is and how you could measure plant-based diets between a thousand other variables just involving food I think it is close to impossible to really study this. – Borgh Jan 9 at 8:17

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