I found this study that a ketogenic diet improved some cognitive scores in some patients with mild alzheimer's [1]. The diet is also sometimes prescribed for intractable epilepsy [2]. There is also a link between epilepsy and alzheimer's, with some AD patients having seizures as the disease progresses (like in Jo's case).

1. https://www.ncbi.nlm.nih.gov/pubmed/19664276

2. https://www.epilepsy.com/learn/treating-seizures-and-epileps...