And this may explain why UnitedHealth was one of the stocks Buffett bought in Q2. Following its recent slump, UNH's forward price-to-earnings (P/E) ratio is now at 16.5 – below both its five-year average of 19.2, according to Morningstar, and the S&P 500's forward P/E ratio of 23.3.

Key Takeaways Warren Buffett's Berkshire Hathaway increased its holdings in UnitedHealth Group stock.A regulatory filing showed Berkshire held 5 million shares in the second quarter.Berkshire also added positions in D.