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 Medifast Inc. (NYSE:MED) were looking healthier today, gaining as much as 10% after reporting fourth-quarter earnings last night and announcing an expansion into Canada.

So what: The weight-loss management specialist said that revenue declined 7% to $77.3 million, worse than estimates, though earnings of $0.39 per share topped expectations at $0.36. CEO Michael MacDonald noted that the company improved operating margin by 480 points in the quarter, helping it to nearly double operating income to $7.0 million. Separately, the company announced it would expand into Canada in the first quarter, beginning by selling through its e-commerce site. 

Now what: While the Canadian expansion will grow Medifast's addressable market by 30 million consumers, the company's guidance was still light for the coming year. Management said it expects revenue of $340 million to $380 million, against estimates of $373 million, and EPS of $1.80-$1.90, below the consensus at $1.93. The improvement in operating margin may be encouraging, but given the flat revenue guidance and downside EPS outlook, today's jump looks exaggerated.