Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of GNC Holdings Inc (NYSE:GNC) were looking unhealthy today, falling as much as 19% after an underwhelming first-quarter earnings report.

So what: The retailer of health and wellness products saw sales flatten in the quarter, as comparable sales fell 0.7%, and overall revenue grew just 1.9% to $677.3 million, missing estimates at $695.9 million. Earnings per share, meanwhile, improved from $0.73 a year ago to $0.75, but that was $0.01 short of the consensus. CEO Joe Fortunato said severe weather affected sales by delaying the start of the workout season. He also said that "negative media" was weighing on current sales trends. 

Now what: Fortunato did not provide specifics about the negative media attention, but reports have circulated in various outlets questioning the efficacy of strength and dietary supplements that are a hallmark of GNC. Fortunato also said he expected the weak sales trends to continue over the next few quarters, which resulted in a reduced EPS guidance of $3.05-$3.10 for the full year on a mid-single-digit increase in revenue. Analysts had expected a per-share profit of $3.20 for 2014 on 8% top-line growth. Given the industry-wide headwinds, I'd stay away from GNC until trends begin to favor the nutrition retailer once again.

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Jeremy Bowman has no position in any stocks mentioned. The Motley Fool has no position in any of the 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.