For some type of epilepsy, neurologists recommend an extremely low-carbohydrate diet. This will force the body to breakdown fat as an energy source. What by-product of breaking down fat can also be used by the brain as an energy source?

Investigator a has biological specimens that are coded and linked to identifiers of the source individuals. investigator a provides the specimens to investigator b but does not provide the individual identifiers. investigator b agrees not to re-identify the source individuals. is investigator b's research using the biospecimens human subjects research according to the definition of human subjects research in the federal regulations?