Mars M&M chocolates. Adam Jeffery | CNBC

Warren Buffett speaks to CNBC's Andrew Ross Sorkin CNBC

But the paths for both companies since their deals have been diametrically divergent, and as has, thus far, the return on the billionaire's investment. The contrast in fortunes can be attributed to many forces. Even as tastes have changed, consumers are more wiling to pay up for their favorite brand of chocolate than they are for cheese. Today's indulgences are more likely to be small and snackable, like a bag of M&M's or a Twix candy bar, and they are less likely to include processed foods like an Oscar Meyer bologna sandwich. Led by the Mars family, the company has decades of experience in running the confectionery empire, which also includes a petcare business. Kraft Heinz is led by 3G Capital, the private equity firm that has proved itself in dealmaking and cost-cutting but not yet in running the day-to-day operations of a food company. But there is another force at play, which speaks more broadly to the pressures facing the consumer industries at large: Mars is a private company while Kraft Heinz is public. Unlike the confectionery giant, Kraft Heinz has had to battle the changes in the consumer industry under the public pressure of quarterly earnings. For any company, that spotlight can be harsh; for a food company over the past few years, it has been nearly impossible. Companies from General Mills, Campbell and Kraft Heinz are grappling with vast portfolios of brands that Americans are no longer eating. Sales across food companies are generally stagnant or declining, forcing many of them to take large, expensive bets.