Pre-Employment Medical Screening?

(Mods feel free to delete if this doesn't belong here)

I got my first big boy job out of college at this company a couple of weeks ago. It's a desk job, part-time hours, and after I cleared my background check, they told me now I have to pass my drug/medical screening.

The drug screening I can understand, but I've never heard of a medical screening for something like a desk job. Can anyone help shed light on what this entails and how one would "fail" it?

I'm also overweight and possibly pre-diabetic, would this compromise my job offer?

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