The U.S. restaurant industry is in a funk. Blame it on lunch.

Americans made 433 million fewer trips to restaurants at lunchtime last year, resulting in roughly $3.2 billion in lost business, according to market-research firm NPD Group Inc. It was the lowest level of lunch traffic in at least four decades.

While that loss in traffic is a 2% decline from 2015, it is a significant one-year drop for an industry that has traditionally relied on lunch and has had little or no growth for a decade.

"I put [restaurant] lunch right up there with fax machines and pay phones," said Jim Parks, a 55-year-old sales director who used to dine out for lunch nearly every day but found in recent years that he no longer had room for it in his schedule.

The decline in lunch business is horrible for restaurants and horrible for people who want to go out from time to time but will find themselves without their favorite restaurants if enough people follow their frugal and time-saving lead to sit at their desk and eat leftovers. Now, I'm never going to tell someone that it's their duty to prop up another business rather than use money wisely. But I will say you need to step away from your desk.

Josh Davis, director of research at the NeuroLeadership Institute and author of Two Awesome Hours: Science-Based Strategies to Harness Your Best Time and Get Your Most Important Work Done advocates taking a two-hour lunch every day. He says if you take that break you'll end up being more productive.

While this sounds awesome, it may not be entirely practical depending on your job, and your commute, and your family situation, but his point is that you need a break in the middle of the day. Your brain needs a bit of a rest.

In the past, lunch provided that. Today, fewer people take that break every day. And with our phones tethering us to the working work, even when we are way from the office, eating at a restaurant doesn't seem that much different than eating at your desk.

If you want to help save restaurants, go to lunch at a restaurant (although, I'll have to advise you to skip the three martinis). But if you can't afford the cost--either in dollars or calories--at least leave work for an hour every day. Go to the gym. Go on a walk. Eat a sandwich in the park. Take a break. You'll be more productive if you do.