[_yb2s]

Technically I think the "brain energy" hypothesis is probably correct from a mechanistic perspective... in fact virtually all diseases can be seen from a lens of metabolic energy not flowing into the correct systems that would be able to restore normal function- even communicable diseases are technically treatable by getting enough energy into the right immune response.

That said, it's more of a theoretical framework that could lead to developing treatments in the long term future... we don't have treatments now that can carefully manipulate and restore metabolic function to the right areas for treating most illnesses. If it were as simple as you (and others) are implying, one could basically treat all mental illness successfully with thyroid hormones. That probably does work for some people, but if it were broadly effective, it would be more obvious.

The idea that things are genetic, metabolic in nature, and/or treatable with nutrients and diet are not in any way mutually exclusive. All conditions involve an interaction between genetics and environment. Presumably, many genetic diseases could be mitigated or prevented in theory with a properly engineered/controlled environment, if we had enough understanding of how to do so.