At some point in your life, you've heard the saying that "breakfast is the most important meal of the day." Restaurants are now taking heed to the adage and are expanding their business to cater to the first meal of the day.

According to the NPD Group, the food service industry is seeing its highest levels of traffic in six years. Morning meal/breakfast continues to grow at the fastest pace among all meal dayparts with a 4 percent jump in visits at all restaurants and foodservice outlets.

"It makes sense that we will be seeing more chain and independent operators leverage the growth areas, like breakfast, in the coming months," says Bonnie Riggs, NPD's restaurant industry analyst.

The most notable restaurant catering to the increased popularity and demand for breakfast is McDonald's. On Oct. 6, the fast food chain rolled out its all-day breakfast menu in hopes to spearhead the increasing slump the fast food company has been experiencing in recent months.

According to Technomic, McDonald's makes up 31 percent of all fast food chain breakfast sales, with the Egg McMuffin being the industry's best-selling breakfast sandwich. Breakfast sales make up about 25 percent of the company's sales. By extending breakfast, the company could see sales increase by as much as 2.5 percent a year. It could also increase consumers' numbers by as much as 2.3 percent.

Although McDonald's now serves breakfast throughout the day, the entire breakfast menu is not available after the mealtime's initial cutoff. Breakfast menu regulars such as hashbrowns, oatmeal and the sausage burrito are available all day, but Egg McMuffins or biscuit sandwiches may not be available, depending on location.

McDonald's is not the only restaurant looking to increase business through breakfast.

In September, White Castle expanded their breakfast menu and began to serve breakfast under their new "Anything, Anytime" menu.

"We feel it's our civic duty to be able to give people what they want, when they want it," said Jamie Richardson, White Castle vice president. "It's 2015. We should be able to do that."

Restaurants already serving breakfast all day do not seem to be threatened with the new competition.

"I don't think we need to respond at all," Nigel Travis, CEO of Dunkin' Brands, told CNBC. "We have in our view the best breakfast out there. We've been advertising the fact that we have all-day breakfast."

Other brands took to Twitter to express their opinions when it came to McDonald's coming into the fold of serving all-day breakfast. Several chains such as IHOP and Denny's used the hashtag #AllDayBreakfast to voice their thoughts on the new competition.

Last year, breakfast sales reached $34.5 billion. Those restaurants who have expanded into breakfast have seen an increase in sales, including Taco Bell.

Breakfast accounts for 6 percent in sales for Taco Bell. Seeing breakfast as a success, the chain is expected to expand its breakfast options with its new line of Biscuit Tacos.

"We have a lot of Taco Bell users who are already eating breakfast in the food-food industry," said taco Bell CEO Brian Niccol. "We still have a big opportunity on getting people aware that Taco Bell is open for breakfast."

According to an NPD report, breakfast sandwiches are projected to outpace the industry's growth forecast. Annual servings per capita are expected to jump from 11 in 2004 to 14 in 2019.

"There is a lot of activity around the breakfast daypart right now, with chains expanding into the daypart, and the addition of breakfast menu items, promotions and deals," Riggs said. "Currently only 1 out of 10 breakfast opportunities is satisfied by food service, and there are more breakfasts skipped than served in restaurants, all of which means that breakfast is a significant growth opportunity for the food service industry."