The university of Iowa did an analysis of the US National Health Interview Survey data from 1997 to 20161. They came out with a correlation between autism and food allergies.
The data is interview based, so if someone thought they had a food allergy they mentioned it. Not a clinical result but may warrant further investigation.
Guifeng Xu, MD; Linda G. Snetselaar, PhD; Jin Jing, MD, PhD; et al, Association of Food Allergy and Other Allergic Conditions With Autism Spectrum Disorder in Children JAMA Netw Open. 2018;1(2):e180279. doi:10.1001/jamanetworkopen.2018.0279