Diet obsession

No, I’m not about to enlighten you on my dieting habits, which are quite absent of self-control. I’m writing to vent about a certain person at work who seems a bit obsessed with my diet.
From our little half cubicles in the office everyone can see almost everyone else. There is not much privacy at all, which is understandable...why should there be? I sit in plain sight of someone who has the unnerving habit of watching every little bite I put into my mouth all day long.
This person watches as I eat my daily snacks of pecans, chocolate covered pretzels, grapes, more chocolate, popcorn, and dried fruit. He/she watches again as I heat up my lunch and devour it like a starved child. Sometimes comments are made.
“Oh, look, you’re eating an apple.” or “MMMMMmmmm, how I love popcorn.” or “Wow, eating again, already.”
This person, who happens to be rail skinny, walks around all day offering food, candy, and beverages to me. He/she is extremely nice and generous. I’ve said no to every single offering, but yet they still come day in and day out.
I guess the part that bothers me most is the whole being watched thing. I feel I’m under a microscope. I personally avoid keeping track of my diet at all costs. That way I don’t know the damage. Why would I want someone else to keep track of it for me?