Not allowed to eat

I work inside of a big department store. I don't work for the store, I work for a leasing company inside the store. 99% of the time i am the only one working in my area. There isn't anyone to watch my store while I pee, eat, etc. so I run to the back to warm up my food. I eat my food at my store. And no, I cannot close the store during my break.

The department store people are mad because I am eating on the floor, but I have no choice. They tell me to ask the customer service people to watch the store but a) there's not enough of them for them to keep an eye on it and b) they don't know my product, so if someone comes up to my store, they won't be able to help them and the customer will be mad at me and my store.

I just got chewed out and I'm thoroughly pissed off, especially because I have multiple stomach issues that require me to eat multiple times throughout a shift. (Typically 7-8 hours mind you).