I don't want them to. I'm not giving them that data myself and I don't consent to McDonalds giving them that data either, where that data is something I have to McDonalds. It's about information asymmetry.
I would like to assume that people aren't generally so ignorant of how insurance works that they think the risk of eating two big macs a week could be accurately priced in and that insurance companies would not just use the fact of eating a couple to justify an unsupported by actuarial analysis rate increase.
Once again, my assumptions of people prove misguided.