I found a little Serendipity in Naiman's revealings. My sister just got some dna results, she came in homozygous for the MTHFR variant that boogers up folate metabolism. Naiman specifically mentioned people coming in with low folate levels. In an old thread on this forum Regina Wilshire discussed this as a possible issue on muscle-meat-only carnivore diets, not necessarily an argument vs. carnivore, more of an argument for some liver, eggs etc. Is this an issue for everybody? Maybe not. Should it be ignored as a possible issue? Probably not.

A few years ago I had the most purely manic episode of my life, before then the stronger manic episodes were mixed with more schizo- stuff like auditory hallucinations, the illusion that people could hear my thoughts and vice-versa. I was taking a number of cognition-related nutrients then, trying to see if I could shake something loose social anxiety wise. Afterwards I found a small study where creatine had an antidepressant effect, but the 2 out of 10 depressives in the study who were also bipolar switched to manic. MTHFR/folate drives methylation, and the synthesis of creatine demands more methylation than all the other methylation processes combined. Methylation produces homocysteine, and creatine supplementation does decrease homocysteine levels.

I guess you could make an argument that large amounts of red meat might decrease at least the creatine fraction of folate requirement. Who knows, maybe increased dietary creatine is a factor in some of those cases like Amber O'Hearn or Michaela Peterson where all or mostly beef diets look to be working vs. depression.