Which amino acid is known to be ketogenic and glucogenic?

Isoleucine is known to be both ketogenic and glucogenic, making it a unique amino acid among the options provided. Ketogenic amino acids are those that can be converted into ketone bodies, while glucogenic amino acids can be converted into glucose through gluconeogenesis.

Isoleucine can undergo catabolism pathways that lead to the production of both acetyl-CoA, which contributes to ketogenesis, and succinyl-CoA, which can be used in gluconeogenesis to generate glucose. This dual capability allows isoleucine to play versatile roles in energy metabolism, depending on the body's needs.

In contrast, while phenylalanine, tryptophan, and threonine each have their own unique metabolic pathways, they do not have the same dual capacity as isoleucine. Phenylalanine is primarily glucogenic, tryptophan is also more associated with gluconeogenesis, and threonine has a more complex metabolism that does not definitively categorize it as both ketogenic and glucogenic like isoleucine does.