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.

For the second day in a row, the Dow Jones Industrial Average (INDEX: ^DJI) is underperforming the broader market, down a few points as of 12:25 EDT as the S&P 500 and other market indexes rise. Big gains in technology stocks explain much of the disparity, with Google shares topping the $1,000 mark and leading the Nasdaq Composite up more than 0.9%.

McDonald's (NYSE: MCD) earnings report on Monday morning will mark the beginning of another important week for Dow-component earnings. The fast-food giant will release results before the bell and then hold its quarterly conference call shortly thereafter. What McDonald's reveals will be important not just for its own business, but also as a sign of conditions throughout the food industry.

McDonald's has gone through tough times lately as food-related scares in China and sluggish growth in its more mature market regions have combined to pressure the company's financial results. In particular, McDonald's same-store sales have been weak lately, and this quarter's results don't look likely to reverse that trend. July same-store sales were up just 0.7% worldwide, with European comps and same-store sales for McDonald's Asia-Pacific, Middle East, and Africa segment both dropping by 1.9%. August showed some improvement, with global comps climbing to 1.9% thanks largely to a big rebound in Europe. McDonald's U.S. sales were up during both months but remained fairly sluggish.

McDonald's has done its best to respond to increased competition from its fast-food rivals. A combination of menu revamps and store renovations could help boost McDonald's reputation, especially in the face of competition both from other fast-food specialists and from fast-casual, higher-scale peers.

Dow investors should care about McDonald's not merely because of its status as a Dow component, but also because it reflects the health of the food industry. Many other Dow components rely on food as a major part of their businesses, whether it's Wal-Mart's fast-growing grocery operations, Coca-Cola's soft-drink empire, or DuPont's growing emphasis on seeds and other agricultural products.

Profit from American domination
McDonald's has been an important part of the Dow ever since it joined the average in 1985. As a hallmark of American culture, McDonald's symbolizes America's ability to expand across the globe and create big profits wherever it goes.