You are what you eat

And eating a heavy mid-day meal will often make you feel lethargic for the rest of the afternoon. "Consider what you're eating at lunch. If you're having that post-pasta slump at 2 p.m., and need java or cookies to pep back up, maybe you should try a salad or something a bit lighter so you won't lag," suggests Hohlbaum.

The key is keeping your blood sugar levels steady throughout the day, according to Kari Kooi, RD, corporate wellness dietician at The Methodist Hospital in Houston, who recommends three light meals and two snacks at regular intervals. "Heavy meals can make you feel sluggish because they require more energy to digest," Kooi says. "[A quality lunch] will consist of a fiber-rich carbohydrate, like water-rich veggies, and a lean protein, like chicken or fish," she says.

And what does Kooi suggest you avoid? "A highly processed meal, like some of the frozen meals in the grocery store, will not give you the sustainable energy you need. The less processed the better when it comes to keeping your energy levels up." When you hit that midday slump, Kooi suggests going for proteins like mixed nuts and fruit instead of the usual energy-zapping pretzels, cookies or candy, which cause your blood sugar levels to spike and then drop and may even make you hungrier, according to Kooi.