Is there a relationship between body composition and intelligence? Does being fat or thin have any significant effect on cognition? For example, I have observed some very fat people who are extremely intelligent and some very thin people that are not and vice versa. John von Neumann was fat and very smart. Are there any studies on this?
A systematic meta-analysis of the relationship between IQ and obesity (Yu, Han, Cao and Guo, 2010) suggested that lower IQ in childhood was associated with later adult obesity via educational level. No evidence of a relationship between IQ and obesity was found for adults.


  Our study and review of the literature overall suggests that there are inverse FIQ/obesity associations, except in pre-school children. However, after adjusting for educational attainment, this FIQ/obesity association became null. In the present study, a lower IQ score in childhood is associated with obesity in later adulthood; this relationship is perhaps mediated via educational attainment in later life.


References


Yu, Z. B., Han, S. P., Cao, X. G., &amp; Guo, X. R. (2010). Intelligence in relation to obesity: a systematic review and meta‐analysis. Obesity reviews, 11(9), 656-670.