AITA for not wanting to split groceries with my roommate?

I (24F) have been living with my roommate Sarah (26F) for about a year now. We get along well for the most part, she’s clean, pays rent on time, and isn’t one of those horror story roommates you read about. But there’s been this growing tension over our grocery situation that I can’t shake, and I’m wondering if I’m being petty.

When we first moved in together, Sarah suggested we do a joint grocery budget to "make things easier." She had lived with roommates before, and she said it was way more convenient to just split the cost and share everything instead of trying to keep track of separate groceries. I agreed because it did sound easier, and at the time, I assumed we had similar eating habits. We each put in $200 a month, which seemed reasonable.

But over time, I realized Sarah eats way more than I do. For context, I work in an office and usually grab lunch while I’m out. Sometimes, I even skip breakfast if I’m running late and just grab coffee at work. That means I’m mainly eating at home for dinner, and even then, I cook simple meals like pasta, salads, eggs, stuff like that. Sarah, on the other hand, works from home and eats all her meals from our groceries. She also snacks constantly. I’ll buy a box of granola bars, and they’re gone in two days. If I get yogurt, I might have one before she’s finished the entire pack. And don’t even get me started on things like chips or cereal. I’ve literally never finished a full bag before she does.

At first, I let it slide. I figured it evened out in some way I wasn’t noticing. But then I started tracking what I was actually eating compared to what she was eating, and it wasn’t even close. I brought it up casually once, like, "Hey, I feel like I don’t eat as much as you, maybe we should adjust how much we each contribute?" She kind of laughed and said, "Oh, I just eat what’s there! Just grab more next time."

So I started trying to buy things just for myself, stuff I knew she wouldn’t like. I got almond butter instead of peanut butter, flavored oat milk she once said she hated, and a weird brand of protein bars. Somehow, even those disappeared.

Last month, I finally told her we should rethink the split. I suggested a system where we either contribute based on consumption or just buy our own food separately. She got really defensive, saying it’s "too much of a hassle" to track who eats what and that "we agreed to share." She also accused me of "nickel-and-diming" over food and making things weird.

I don’t want to be stingy, but at the same time, I don’t think it’s fair to pay half when I’m eating maybe a third of what she is. She’s been acting cold ever since, and I’m wondering am I being unreasonable here or is she just taking advantage?