My friend eats all my food!?

my best friend works in the same office with me. lately i've been trying to eat healthy food, so i take nutritious snacks to eat throughout the day. i don't want to be mean or make a big deal out of this but my friend always eats half or more of my food and it's driving me crazy. health food is not cheap and i am definitely not rich. i don't mind sharing usually, but it annoys me that she automatically feels entitled to a share of my food. she even comes and asks for it, so it's not like i can hide it. then she starts talking about how money is tight (yet she has taken food to some guy she likes)...
i don't want to be a bad friend, but i'm annoyed. and i don't know what i can do because she is very delicate, and will take offense (get angry) to anything.

grrr....

lol. thanks guys :p

lol maybe suggest that your food is to help with health issues or maybe make comment as to say i would like to share with you however i had to mix my medication in food to get down easily if not to hurt ones feelings if you dont feel comfortable to straight forward tell her shes being a pain in your back end

Just add it in to your budget. She's broke and needs charity.

Make little jokes about all the wieght your losing becuase you never get to eat.

Tell her very casually and nicely that your doctor told you that you need to eat healthier (a little lie couldn't hurt) and that it is gettin gquite expensive, and as much as you would like to share your food, you simply cant afford it. So if you could please stop eating my food that would be really great.