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 analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of GNC Holdings (NYSE:GNC) slipped about 1.5% in premarket trading Thursday after Jefferies downgraded the health supplements retailer from buy to hold.

So what: Along with the downgrade, analyst Mark Wiltamuth lowered his price target to $39 (from $50), representing about 10% worth of upside to yesterday's close. So while momentum traders might be turned off by GNC's year-to-date price weakness, Wiltamuth's call could reflect a sense on Wall Street that its growth prospects are just too limited to trigger a significant rebound.

Now what: Jefferies lowered its 2014 EPS estimate for GNC from $3.07 to $3.00 and its 2015 view from $3.56 to $3.35. "We have been wrong on GNC as we've been caught in a value trap waiting for sales to snap back. Industry data now suggests a broader slowdown is under way," said Wiltamuth. "We see risk of a near-term earnings disappointment and with industry sales trends weaker, analysts may have to rethink 2015 estimates and long-term growth rates. While valuation is at record lows, we fear EPS estimates are still falling." With the stock flirting with its 52-week lows and currently sporting a forward P/E of 10, however, those short-term concerns might be providing patient Fools with a healthy long-term opportunity.

Brian Pacampara has no position in any stocks mentioned.Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.