Thank you, Little Turtle, for bringing up the issue of hormonal activity in body - and brain - homeostasis.
Just for reference:
a PubMed abstract on leptin and ghrelin.
I like the following saying: "It's not that 'you are what you eat,' it's 'you are what your body does with what you eat.'"
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My dog
mastered the "fetch" command. He would communicate he wanted something, and I would fetch it.