Correlation is not Causation: You might want to look at the prevalence of infectious diseases by race according to the CDC.
https://www.cdc.gov/nchhstp/healthdisparities/africanamerica...
Edit: Insert Numbers;
Black People make up 14% of US population and
45% of the total of HIV/Aids
62% of women with HIV/Aids
55% of Gonorrhea
Chalmydia: Black Women 5.2x more likely and Black men 7.3 times more likely as white people
38% of Syphilis cases Black Men and Women over 5 times as likely as white people
37% of TB cases Black people, and 87% of all reported TB cases occurred in racial and ethnic minorities
If the states with lower IQs have a higher percentage of African Americans than the other states, they will have a higher rate of infectious diseases due to the propensity of infectious diseases among that group with respect to others.
PS: The two states with the lowest rate of infectious diseases, Nevada and West Virginia are respectivelly the 2nd and 7th lowest IQ states. #1 lowest IQ, Hawaii was deemed an outlier because of latitude and excluded from the results of the study you linked to.
http://www.americashealthrankings.org/explore/2016-annual-re...
This is strong assumption. Malnutrition (wider concept than just calories) exists in US and there are large differences between ethnic groups.
Interestingly enough, from the same researchers:
Parasite prevalence and the distribution of intelligence among the states of the USA, https://www.researchgate.net/publication/229409035_Parasite_...
>In this study, we tested the parasite-stress hypothesis for the distribution of intelligence among the USA states: the hypothesis proposes that intelligence emerges from a developmental trade-off between maximizing brain vs. immune function. From this we predicted that among the USA states where infectious disease stress was high, average intelligence would be low and where infectious disease stress was low, average intelligence would be high. As predicted, we found that the correlation between average state IQ and infectious disease stress was − 0.67 (p < 0.0001) across the 50 states. Furthermore, when controlling the effects of wealth and educational variation among states, infectious disease stress was the best predictor of average state IQ.Highlights► We compared rates of infectious disease with average IQ across USA states. ► We controlled for education and wealth. ► Infectious disease was the best predictor of average IQ.