The causal link between obesity and low IQ does not seem to be through systemic inflammation. The research I came across suggests that people with lower IQ are

The causal link between obesity and low IQ does not seem to be through systemic inflammation. The research I came across suggests that people with lower IQ are more likely to become obese. > We observed no evidence that obesity contributed to a decline in IQ, even among obese individuals who displayed evidence of the metabolic syndrome and/or elevated systemic inflammation. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3813310/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3813310/ > Overall there was an inverse FIQ/obesity association, except in pre-school children. However, after adjusting for educational attainment, FIQ/obesity association was not significantly different. A lower FIQ in childhood was associated with obesity in later adulthood perhaps with educational level mediating the persistence of obesity in later life. https://www.ncbi.nlm.nih.gov/pubmed/19780990 https://www.ncbi.nlm.nih.gov/pubmed/19780990