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

The earnings season we're just entering may be the most important one of the past few years, as the Federal Reserve begins easing off its economic stimulus. Unfortunately, preliminary results of what's to come don't look very good. With a number of retailers and food and beverage companies updating forecasts this morning, it appears American consumers held back during the fourth quarter of 2013. Those reports helped send the major indexes all lower today. The Dow Jones Industrial Average (DJINDICES:^DJI) lost 179 points, or 1.09%, while the S&P 500 fell 1.26% and the Nasdaq dropped 1.47%.

The Dow's two food and beverage stocks, McDonald's (NYSE:MCD) and Coca-Cola (NYSE:KO), lost 1.01% and 1.5%, respectively, today. Outside sources may be putting pressure on both companies. In the case of McDonald's, competitor Wendy's (NASDAQ:WEN) issued strong full-year earnings guidance this morning and may be gaining ground on the Golden Arches. The No. 2 fast-food company is lowering its costs by franchising more restaurants, which will help it produce higher earnings. Furthermore, while McDonald's has struggled to add new innovative menu options, the recently added pretzel bun is a big hit with customers at Wendy's. The company raised its full-year adjusted earnings per share to a range from $0.34 to $0.36, much higher than Wall Street's consensus estimate of just $0.29. Shares of Wendy's rose 6.4% today. 

As for Coke, investors may be concerned with shrinking soda volumes, as Americans are drinking less soda in general. This morning, SodaStream (NASDAQ:SODA), the maker of home-based carbonated beverage machines, released disastrous preliminary earnings results. Although projected revenue of $562 million is close to the $567.2 million analysts were expecting, net income is expected to be 23% lower than what the Street wanted to see. The likely problem is that SodaStream has been selling more of its starter kits than the higher-margin syrups that make the sodas. Coke investors may therefore be expecting lower volume in its own upcoming quarterly release.  

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Fool contributor Matt Thalman has no position in any stocks mentioned. Check back Monday through Friday as Matt explains what caused the Dow's winners and losers of the day, and every Saturday for a weekly recap. Follow Matt on Twitter: @mthalman5513

The Motley Fool recommends Coca-Cola, McDonald's, and SodaStream and owns shares of Coca-Cola, McDonald's, and SodaStream. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.