It was soon suggested, however, that what was happening was merely a transfer of some necessary nutrients from ingestee to ingester, so that the ingester's task of responding biochemically to the need to create new engrams of its own was proportionately eased. Memory per se had not been transferred in the digestive process, merely a few essentials of protein synthesis. By 1964, many reviewers (eg. Dingman and Sporn, 1964) had weighed the evidence one way and the other, and were coming down heavily against the possibility of a purely molecular engram.
A question when you have a moment ..
Did anyone think to feed NONTRAINED vs. TRAINED food segments to the animals, and then doing a training exercise could be done to test the validity of this 'objection', that merely providing 'nutrients' associated w/ RNA could be the explanation? If true, one would see powerful evidence that Dingman and Sporn asserations were reasonable.
If I am understanding your question right, then they have indeed tested it that way. The article on the link is a summary of the various ways it was tested over several decades.