While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of ConAgra Foods (NYSE:CAG) slipped about 1% in premarket trading Thursday after Bank of America downgraded the food company from buy to underperform.

So what: Along with the two-notch downgrade, analyst Bryan Spillane lowered his price target to $30 (from $34), representing about 2% worth of downside to yesterday's close. So while contrarian traders might be attracted to ConAgra's outlook-related pullback yesterday, Spillane's call could reflect a sense on Wall Street that its growth prospects are just too limited to trigger a significant rebound.

Now what: According to B of A, ConAgra's risk/reward trade-off is pretty unappealing at this point. "While we continue to believe that there is potential for the company to create an advantaged Private Brands business model by delivering higher-quality products at a lower cost, it is clear given yesterday's announcement that it will take longer for the company to realize its full potential," said Spillane. "Valuation is attractive but with muted earnings growth, relatively high debt levels and no dividend growth in the near term we expect the stock to underperform its peers over the next 12 months." With ConAgra shares now off about 20% from their 52-week highs and currently boasting a 3%-plus dividend yield, however, those short-term concerns might be providing patient Fools with a solid long-term income opportunity.