To some extent they do. I've worked at employers who prioritize diet (on site cafe's with posted nutritional information), exercise (on site locker rooms with showers, subsidized gym memberships and reimbursement for employee purchased exercise equipment), work-life balance, etc. I think at this point most employees would bristle a bit if their employer started providing on-site blood tests to check vitamin levels (Imagine the HN threads!), but I could see that changing if it became a more popular thing for people to do on their own.