What's the Deal with Those Phantom Morning Abs?

We've all experienced it: You wake up, look down and think, "Wow, my abs look amazing!" And strangely enough, sometimes they look their best even when the rest of you is feeling its worst-like after a night out. In fact, this phenomenon is so widely experienced that it has its own term and Instagram hashtag: Morning abs.

As you may have guessed, "morning abs" are primarily due to dehydration (hence the whole hangover abs thing, too), explains Joel Martin, Ph.D., C.S.C.S., assistant professor of kinesiology at George Mason University. "You can lose up to several pounds of water weight overnight due to sweating and respiration," he says. (If you're really curious, a good experiment is to weigh yourself at night and again in the morning to see exactly how much.)

The result? More defined muscles, he says. And in this case, those "morning abs."

Not to mention, there's the whole fact that you've essentially been fasting for seven to ten hours while you sleep, says Marni Sumbal, R.D., an exercise physiologist and board-certified sports dietitian. "Unless you ate a high fat/sodium meal late at night, you'll probably wake up and notice less water retention-and thus less bloat," she explains.

Now the bad news: It's physically impossible for your stomach to keep looking the way it does when you first wake up. "You may look more toned in the morning, but as your body processes food, it retains water, and you develop gas/stool-which means a bigger/distended stomach and an overall heavier body," Sumbal explains.

So there you have it: Scientific proof that morning abs are a real thing-and sadly the only way to keep those defined abs all day long is to tone them the good old-fashioned way.