No surprise here. Just one cup of coffee takes us from zombie to superhero all before we've finished checking our morning email. But how exactly does caffeine do that, and why does it work so quickly? For starters, it easily bypasses the blood-brain barrier, the central nervous system's built-in barricade to foreign substances. This filter blocks bacteria, viruses and most drugs from entering the brain. But coffee slips through unimpeded. Within 30 minutes, caffeine has infiltrated the bloodstream and every cell in the body. Consider it the Navy SEAL of substances.

Once it's crossed that barrier, it blocks the activity of adenosine, a neurotransmitter that plays a role in making us tired, explains Marci Clow, MS, registered dietician and senior nutritionist for Rainbow Light supplements. "By blocking adenosine other neurotransmitters, we become more alert," she says. "Studies have found that the caffeine equivalent of about two cups of coffee can enhance cognitive function and mood among sleep-deprived people, and affect the specific areas of the brain responsible for memory and concentration."

All of which is good news for those of us wishing to continue our coffee addiction. Bottoms up!

A good follow-up to that "but first, coffee" mantra that many of us subscribe to could be "and then poop." Yep, if you're among the many who refuse to consume coffee unless there's a toilet nearby, then you know caffeine may make you poop almost as immediately as you consume it. "Coffee promotes peristalsis, which is the contraction and relaxation of the intestinal muscles," says Clow about this curious coffee-poop correlation. "For some people, the bowel-stimulating effect of coffee is a way of keeping regular."

However, since many of us drink our coffee first thing in the morning, a post-coffee poop could also mean your gastrointestinal system is simply revving up at the start of the day -- and coffee is providing a little push of sorts. "Drinking hot water (separate from the coffee beans or added caffeine) also has a stimulating effect," says Nora Zorich, MD, PhD and Chair, Arbonne Scientific Advisory Board. "In this sense, having a bowel movement after the morning coffee is also likely related to other drinking (such as drinking hot water) or eating, which stimulates intestinal contraction waves." But we'll stick with coffee over hot water, thanks, since it gets both our bowels and our minds going in the morning.

You know how you'd rather douse someone with scalding-hot coffee rather than speak to them before having those first few sips of sweet, sweet brew? But once you're caffeinated, you're all ears? That could be because coffee is just as likely to boost mood as it is alertness. "In addition to blocking adenosine receptors, caffeine also affects other major neurotransmitters, including dopamine, acetylcholine and serotonin, delivering a boost even when we are well-rested," says Clow. "Dopamine improves mood, while serotonin makes us more relaxed, alert and energetic." The result is a feel-good rush from out morning coffee -- and useful information to those poor unfortunate souls who have ever dared to interact with us before we've had our first cup.

Wouldn't it be great if there were a magical elixir that helped us burn a few calories? Well, it turns out coffee may do just that. According to a study published by "Physiology and Behavior," people who drank coffee increased their metabolic rate by 16 percent over those who didn't. And as we all know, the faster your metabolism, the more calories you burn. Another bonus? Coffee has been shown to improve endurance levels, meaning if you down your cup before hitting the gym, you can potentially workout longer, and harder, which also translates into burning more calories. Just make sure to skip the cream and sugar because just like our go-to dress, coffee is most slimming when black.