Like other recent health care pairings, the deal — should it go through — marks a pursuit of big data across industries.
Customer data, a longtime preoccupation of retailers, is increasingly seen by health care executives as central to containing rising health care costs….
Having both retail and health businesses under one umbrella could also help push wellness initiatives for customers and health plan members, such as incentivizing healthier food choices, something Humana and Walmart have already worked together on.

I doubt Humana can legally share your medical information with the Walmart side of the business but the Walmart side of the business could share your shopping habits with the insurance side. The insurer would then know what you are buying – and whether your clothing sizes are getting bigger.
Source: Walmart’s potential Humana deal could connect your health insurance with the produce aisle – MarketWatch