Designing studies guaranteed to produce the negative results their authors demand of them is an art form perfected by the manufacturers of monosodium glutamate in the late 1990s.
Having incorporated The Glutamate Association to promote their product, and the International Glutamate Technical Committee to design and implement research which they would claim demonstrates the safety of MSG, they found medical journals to publish their studies, print, internet, and TV sources to carry their interpretations of research results, effectively suppressed any mention that MSG might be toxic, and conspired with the FDA to vouch for the safety of their product.
“Industry’s FDA” elaborates their methods, detailing how they’ve accomplished their mission. The use of excitotoxic (brain damaging) free glutamate in placebos used in their double-blind studies guaranteed the negative results they were looking for in case the rest of their methodology fell short of the goal.
“Industry’s FDA:” https://www.truthinlabeling.org/assets/industrys_fda_final.pdf